Updated on 2022/04/23

写真a

 
MURAOKA Yuji
 
Organization
Research Institute for Interdisciplinary Science Associate Professor
Position
Associate Professor
External link

Degree

  • Ph.D (Sc.)

Research Interests

  • 固体化学

  • Materials science

  • Thin film・Interface

Research Areas

  • Nanotechnology/Materials / Functional solid state chemistry

  • Nanotechnology/Materials / Thin film/surface and interfacial physical properties  / Oxide, Carbon-based materials

Education

  • Tohoku University   大学院理学研究科   化学専攻

    1993.4 - 1996.3

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    Country: Japan

    Notes: 博士後期課程

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  • Tohoku University   大学院理学研究科   化学専攻

    1991.4 - 1993.3

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    Country: Japan

    Notes: 博士前期課程

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  • Tohoku University   理学部   化学科

    1987.4 - 1991.3

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    Country: Japan

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Research History

  • Okayama University   Research Institute for Interdisciplinary Science   Associate Professor

    2016.4

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  • Okayama University   Guraduate School of Natural Science and Technology   Associate Professor

    2007.4 - 2016.3

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  • Okayama University   Guraduate School of Natural Science and Technology   Associate Professor (as old post name)

    2006.4 - 2007.3

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  • The Institute for Solid State Physics, The University of Tokyo   物質設計評価施設   Research Assistant

    2000.3 - 2006.3

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  • COE researcher The Institute of Scientific and Industrial Research, Osaka University

    1998 - 2000

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  • Research Fellow of the Japan Society for the Promotion of Science(PD), IMR, Tohoku University

    1996 - 1998

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  • Researcher on a scholarship of French government, ICMCB, France

    1996 - 1997

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Professional Memberships

Committee Memberships

  • 応用物理学会   代議員  

    2020.2 - 2023.1   

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    Committee type:Academic society

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  • 応用物理学会 中国四国支部   幹事  

    2011.4   

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    Committee type:Academic society

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  • 東京大学物性研究所物質設計評価施設 外部評価委員   外部評価委員  

    2009.4 - 2010.3   

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    Committee type:Other

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Papers

  • Incorporation Site and Valence State of Sn Atoms in Sn-Substituted La(O,F)BiS2 Superconductor Reviewed

    YaJun Li, ZeXu Sun, Noriyuki Kataoka, Taro Setoguchi, Yusuke Hashimoto, Soichiro Takeuchi, Shunjo Koga, Takayuki Muro, Satoshi Demura, Kanako Noguchi, Hideaki Sakata, Tomohiro Matsushita, Ikuto Kawasaki, Shin-ichi Fujimori, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

    J. Phys. Soc. Jpn.   91 ( 5 )   054602   2022.4

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.7566/JPSJ.91.054602

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  • Strain relaxation and spinodal decomposition in composition adjusted TiO2-VO2 films on TiO2(100) substrates Reviewed

    Takahiro Fukuda, Yoshito Takemoto, Takanori Wakita, Takayoshi Yokoya, Yuji Muraoka

    Thin Solid Films   751   139210   2022.4

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    Authorship:Last author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.tsf.2022.139210

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  • Soft x-ray irradiation induced metallization of layered TiNCl Reviewed

    Noriyuki Kataoka, Masashi Tanaka, Wataru Hosoda, Takumi Taniguchi, Shin-ichi Fujimori, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

    Journal of Physics: Condensed Matter   33 ( 3 )   035501 - 035501   2021.1

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

    We have performed soft x-ray spectroscopy in order to study the photoirradiation time dependence of the valence band structure and chemical states of layered transition metal nitride chloride TiNCl. Under the soft x-ray irradiation, the intensities of the states near the Fermi level (E-F) and the Ti3+ component increased, while the Cl 2p intensity decreased. Ti 2p-3d resonance photoemission spectroscopy confirmed a distinctive Fermi edge with Ti 3d character. These results indicate the photo-induced metallization originates from deintercalation due to Cl desorption, and thus provide a new carrier doping method that controls the conducting properties of TiNCl.

    DOI: 10.1088/1361-648x/abbbc3

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    Other Link: https://iopscience.iop.org/article/10.1088/1361-648X/abbbc3/pdf

  • Magnetic-field-induced insulator–metal transition in W-doped VO2 at 500 T Reviewed

    Yasuhiro H. Matsuda, Daisuke Nakamura, Akihiko Ikeda, Shojiro Takeyama, Yuki Suga, Hayato Nakahara, Yuji Muraoka

    Nature Communications   11 ( 1 )   3591   2020.12

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    Metal-insulator (MI) transitions in correlated electron systems have long been a central and controversial issue in material science. Vanadium dioxide (VO2) exhibits a first-order MI transition at 340 K. For more than half a century, it has been debated whether electron correlation or the structural instability due to dimerised V ions is the more essential driving force behind this MI transition. Here, we show that an ultrahigh magnetic field of 500 T renders the insulator phase of tungsten (W)-doped VO2 metallic. The spin Zeeman effect on the d electrons of the V ions dissociates the dimers in the insulating phase, resulting in the delocalisation of electrons. As the Mott-Hubbard gap essentially does not depend on the spin degree of freedom, the structural instability is likely to be the more essential driving force behind the MI transition.

    DOI: 10.1038/s41467-020-17416-w

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    Other Link: http://www.nature.com/articles/s41467-020-17416-w

  • Formation of Q-carbon by adjusting sp3 content in diamond-like carbon films and laser energy density of pulsed laser annealing Reviewed

    Hiroki Yoshinaka, Seiko Inubushi, Takanori Wakita, Takayoshi Yokoya, Yuji Muraoka

    Carbon   167   504 - 511   2020.10

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.carbon.2020.06.025

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  • Change in the electronic structure of the bismuth chalcogenide superconductor CsBi4-xPbxTe6 by dissociation of the bismuth dimers Reviewed

    Hiroyuki Okazaki, Kensei Terashima, David Billington, Keiji Iwata, Takanori Wakita, Masashi Tanaka, Yoshihiko Takano, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF PHYSICS-CONDENSED MATTER   32 ( 14 )   145501-1 - 145501-7   2020.4

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  • Change in the work function of VO2 thin film across the metal-insulator transition in VO2/TiO2:Nb(001) heterostructures Reviewed

    Yuji Muraoka, Yuki Suga, Hayato Nakahara, Takayoshi Yokoya

    JPS Conf. Proc.   30   011071 - 011071   2020.3

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    Authorship:Lead author   Language:English   Publishing type:Research paper (international conference proceedings)   Publisher:IOP Publishing  

    Abstract

    We have performed soft x-ray spectroscopy in order to study the photoirradiation time dependence of the valence band structure and chemical states of layered transition metal nitride chloride TiNCl. Under the soft x-ray irradiation, the intensities of the states near the Fermi level (EF) and the Ti3+ component increased, while the Cl 2p intensity decreased. Ti 2p–3d resonance photoemission spectroscopy confirmed a distinctive Fermi edge with Ti 3d character. These results indicate the photo-induced metallization originates from deintercalation due to Cl desorption, and thus provide a new carrier doping method that controls the conducting properties of TiNCl.

    DOI: 10.1088/1361-648x/abbbc3

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    Other Link: https://iopscience.iop.org/article/10.1088/1361-648X/abbbc3/pdf

  • Strain effects on spinodal decomposition in TiO2-VO2 films on TiO2(100) substrates Reviewed

    Yuji Muraoka, Fumiya Yoshii, Takahiro Fukuda, Yuji Manabe, Mikiko Yasuno, Yoshito Takemoto, Kensei Terashima, Takanori Wakita, Takayoshi Yokoya

    Thin Solid Films   698   137854   2020.2

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  • Electronic structure changed by Bi dimer in bismuth chalcogenide superconductor CsBi4-xPbxTe6 Reviewed

    Hiroyuki Okazaki, Kensei Terashima, David Billington, Keiji Iwata, Takanori Wakita, Masashi Tanaka, Yoshihiko Takano, Yuji Muraoka, Takayoshi Yokoya

    J. Phys.:Condens. Matter   32 ( 12 )   145501   2020.1

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  • µ-PES Studies on TiNCl and Quasi-two-dimensional Superconductor Na-intercalated TiNCl Reviewed

    Noriyuki Kataoka, Kensei Terashima, Masashi Tanaka, Wataru Hosoda, Takumi Taniguchi, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

    Journal of the Physical Society of Japan   88 ( 10 )   104709 - 104709   2019.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Physical Society of Japan  

    DOI: 10.7566/jpsj.88.104709

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  • Asymmetric Phosphorus Incorporation in Homoepitaxial P-Doped (111) Diamond Revealed by Photoelectron Holography Reviewed

    T. Yokoya, K. Terashima, A. Takeda, T. Fukura, H. Fujiwara, T. Muro, T. Kinoshita, H. Kato, S. Yamasaki, T. Oguchi, T. Wakita, Y. Muraoka, T. Matsushita

    Nano Lett.   19   5915 - 5919   2019

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    DOI: 10.1021/acs.nanolett.9b01481

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  • Enhanced thermoelectricity by controlled local structure in bismuth-chalcogenides Reviewed

    K. Terashima, Y. Yano, E. Paris, Y. Goto, Y. Mizuguchi, Y. Kamihara, T. Wakita, Y. Muraoka, N. L. Saini, T. Yokoya

    J. Appl. Phys.   125   145105   2019

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1063/1.5087096

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  • Origins of Thermal Spin Depolarization in Half-Metallic Ferromagnet CrO2 Reviewed

    Hirokazu Fujiwara, Kensei Terashima, Masanori Sunagawa, Yuko Yano, Takanobu Nagayama, Tetsushi Fukura, Fumiya Yoshii, Yuka Matsuura, Makoto Ogata, Takanori Wakita, Koichiro Yaji, Ayumi Harasawa, Kenta Kuroda, Shik Shin, Koji Horiba, Hiroshi Kumigashira, Yuji Muraoka, Takayoshi Yokoya

    Physical Review Letters   121 ( 25 )   2018.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society (APS)  

    DOI: 10.1103/physrevlett.121.257201

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.121.257201/fulltext

  • Direct observation of double valence-band extrema and anisotropic effective masses of the thermoelectric material SnSe Reviewed

    Takanobu Nagayama, Kensei Terashima, Takanori Wakita, Hirokazu Fujiwara, Tetsushi Fukura, Yuko Yano, Kanta Ono, Hiroshi Kumigashira, Osamu Ogiso, Aichi Yamashita, Yoshihiko Takano, Hitoshi Mori, Hidetomo Usui, Masayuki Ochi, Kazuhiko Kuroki, Yuji Muraoka, Takayoshi Yokoya

    JAPANESE JOURNAL OF APPLIED PHYSICS   57 ( 1 )   010301   2018.1

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    Synchrotron-based angle-resolved photoemission spectroscopy is used to determine the electronic structure of layered SnSe, which was recently turned out to be a potential thermoelectric material. We observe that the top of the valence band consists of two nearly independent hole bands, whose tops differ by similar to 20meV in energy, indicating the necessity of a multivalley model to describe the thermoelectric properties. The estimated effective masses are anisotropic, with in-plane values of 0.16-0.39 m(0) and an out-of-plane value of 0.71 m(0), where m(0) is the rest electron mass. Information of the electronic structure is essential to further enhance the thermoelectric performance of hole-doped SnSe. (C) 2018 The Japan Society of Applied Physics

    DOI: 10.7567/JJAP.57.010301

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  • Martensitic transformation induced in Ti-15V-7Al alloy at low and high temperatures Reviewed

    Y. Takemoto, M. Tsunekawa, Y. Manabe, S. Itano, Y. Muraoka

    Mater. Trans.   59   1560 - 1566   2018

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.2320/matertrans.M2018185

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  • Fermi surface topology in a metallic phase of VO2 thin films grown on TiO2(001) substrates Reviewed

    Yuji Muraoka, Hiroki Nagao, Yuichiro Yao, Takanori Wakita, Kensei Terashima, Takayoshi Yokoya, Hiroshi Kumigashira, Masaharu Oshima

    Sci. Rep.   8   17906   2018

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    DOI: 10.1038/s41598-018-36281-8

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  • Multilayer formation via spinodal decomposition in TiO2-VO2 epitaxial films on sapphire substrates Reviewed

    Yuka Matsuura, Fumiya Yoshii, Tsubasa Otsuka, Kenji Kadowaki, Masataka Ijiri, Yoshito Takemoto, Kensei Terashima, Takanori Wakita, Takayoshi Yokoya, Yuji Muraoka

    J. Eur. Ceram. Soc.   38   5043 - 5050   2018

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.jeurceramsoc.2018.07.035

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  • Determination of the local structure of Sr2-xMxIrO4 (M = K, La) as a function of doping and temperature Reviewed

    Kensei Terashima, Eugenio Paris, Eduardo Salas-Colera, Laura Simonelli, Boby Joseph, Takanori Wakita, Kazumasa Horigane, Masanori Fujii, Kaya Kobayashi, Rie Horie, Jun Akimitsu, Yuji Muraoka, Takayoshi Yokoya, Naurang Lal Saini

    Phys.Chem.Chem.Phys.   20 ( 36 )   23783 - 23788   2018

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:ROYAL SOC CHEMISTRY  

    The local structure of correlated spin-orbit insulator Sr2-xMxIrO4 (M = K, La) has been investigated by Ir L-3-edge extended X-ray absorption fine structure measurements. The measurements were performed as a function of temperature for different dopings induced by substitution of Sr with La or K. It is found that Ir-O bonds have strong covalency and they hardly show any change across the Neel temperature. In the studied doping range, neither Ir-O bonds nor their dynamics, measured by their mean square relative displacements, show any appreciable change upon carrier doping, indicating the possibility of nanoscale phase separation in the doped system. On the other hand, there is a large increase of the static disorder in Ir-Sr correlation, larger for K doping than La doping. Similarities and differences with respect to the local lattice displacements in cuprates are briefly discussed.

    DOI: 10.1039/c8cp03756f

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  • Temperature-dependent local structure and superconductivity of BaPd2As2 and SrPd2As2 Reviewed

    K. Terashima, E. Paris, L. Simonelli, E. Salas-Colera, A. Puri, T. Wakita, Y. Yamada, S. Nakano, H. Idei, K. Kudo, M. Nohara, Y. Muraoka, T. Mizokawa, T. Yokoya, N. L. Saini

    Phys. Rev. B   98   09425   2018

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    DOI: 10.1103/PhysRevB.98.094525

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  • Observation of intrinsic half-metallic behavior of CrO2 (100) epitaxial films by bulk-sensitive spin-resolved PES Reviewed

    Hirokazu Fujiwara, Masanori Sunagawa, Kensei Terashima, Tomoko Kittaka, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA   220   46 - 49   2017.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

    We have investigated the electronic states and spin polarization of half-metallic ferromagnet CrO2 (100) epitaxial films by bulk-sensitive spin-resolved photoemission spectroscopy with a focus on non-quasiparticle (NQP) states derived from electron-magnon interactions. We found that the averaged values of the spin polarization are approximately 100% and 40% at 40 K and 300 K, respectively. This is consistent with the previously reported result [H. Fujiwara et al., Appl. Phys. Lett. 106, 202404 (2015).]. At 100 K, peculiar spin depolarization was observed at the Fermi level (E-F), which is supported by theoretical calculations predicting NQP states. This suggests the possible appearance of NQP states in CrO2. We also compare the temperature dependence of our spin polarizations with that of the magnetization. (C) 2017 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.elspec.2017.02.003

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  • The electronic structure of Ag1-xSn1+xSe2 (x=0.0, 0.1, 0.2, 0.25 and 1.0) Reviewed

    Takanori Wakita, Eugenio Paris, Kaya Kobayashi, Kensei Terashima, Muammer Yasin Hacisalihoglu, Teppei Ueno, Federica Bondino, Elena Magnano, Igor Pis, Luca Olivi, Jun Akimitsu, Yuji Muraoka, Takayoshi Yokoya, Naurang L. Saini

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   19 ( 39 )   26672 - 26678   2017.10

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    We have studied the valence electronic structure of Ag1-xSn1+xSe2 (x = 0.0, 0.1, 0.2, 0.25) and SnSe (x = 1.0) by a combined analysis of X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS) measurements. Both XAS and XPS reveal an increase in electron carriers in the system with x (i.e. excess Sn concentration) for 0 <= x <= 0.25. The core-level spectra (Sn 3d, Ag 3d and Se 3d) show that the charge state of Ag is almost 1+, while that of of Sn splits into Sn2+ and Sn4+ (providing clear evidence of valence skipping for the first time) with a concomitant splitting of Se into Se2- and Se2-delta states. The x dependence of the split components in Sn and Se together with the Se-K edge XAS reveals that the Se valence state may have an essential role in the transport properties of this system.

    DOI: 10.1039/c7cp05369j

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  • Effect of aliovalent dopants on the kinetics of spinodal decomposition in rutile-type TiO2-VO2 Reviewed

    Makoto Ogata, Kenji Kadowaki, Masataka Ijiri, Yoshito Takemoto, Kensei Terashima, Takanori Wakita, Takayoshi Yokoya, Yuji Muraoka

    JOURNAL OF THE EUROPEAN CERAMIC SOCIETY   37 ( 9 )   3177 - 3183   2017.8

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCI LTD  

    The effects of aliovalent dopants on the kinetics of spinodal decomposition in a rutile-type TiO2-VO2 system were studied by means of x-ray diffraction and transmission electron microscopy. In this study, as prepared polycrystalline samples were annealed at 673 k inside the spinodal. For undoped samples, phase decomposition occurred along the [001] direction, and a lamellar structure formed on the nanometer length scale. The phase decomposition kinetics in this system were sensitive to the type of aliovalent dopant; the decomposition rate in a sample doped with Al2O3 was more than one order of magnitude higher than a sample doped with . These observations could be explained on the basis of the premise that cation interstitial mobility is greater than cation vacancy mobility. The obtained results are consistent with those for a TiO2-SnO2 system, indicating that phase separation in both rutile-type oxide systems can be interpreted through a common framework. (C) 2017 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jeurceramsoc.2017.03.039

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  • Evolution of the remnant Fermi-surface state in the lightly doped correlated spin-orbit insulator Sr2-xLaxIrO4 Reviewed

    K. Terashima, M. Sunagawa, H. Fujiwara, T. Fukura, M. Fujii, K. Okada, K. Horigane, K. Kobayashi, R. Horie, J. Akimitsu, E. Golias, D. Marchenko, A. Varykhalov, N. L. Saini, T. Wakita, Y. Muraoka, T. Yokoya

    PHYSICAL REVIEW B   96 ( 4 )   041106(R)   2017.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    The electronic structure of the lightly electron-doped correlated spin-orbit insulator Sr2IrO4 has been studied by angle-resolved photoelectron spectroscopy. We have observed the coexistence of a lower Hubbard band and an in-gap band; the momentum dependence of the latter traces that of the band calculations without on-site Coulomb repulsion. The in-gap state remained anisotropically gapped in all observed momentum areas, forming a remnant Fermi-surface state, evolving towards the Fermi energy by carrier doping. These experimental results show a striking similarity with those observed in deeply underdoped cuprates, suggesting the common nature of the nodal liquid states observed in both compounds.

    DOI: 10.1103/PhysRevB.96.041106

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  • Electronic structure of K-doped picene film on HOPG Reviewed

    T. Wakita, H. Okazaki, T. Jabuchi, H. Hamada, Y. Muraoka, T. Yokoya

    JOURNAL OF PHYSICS-CONDENSED MATTER   29 ( 6 )   26672 - 26678   2017.2

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    We have performed potassium (K)-doping dependent photoemission (PES) measurements of picene film on highly oriented pyrolytic graphite (HOPG). K-doping dependent valence band PES data exhibits a shift of the valence band to a higher binding energy, indicative of the charge transfer from the K atoms to the picene film. K-doping dependent PES spectra near the Fermi level (EF) show the appearance and disappearance of a Fermi edge, indicating the metallic properties of the film at certain K concentrations. High-resolution PES spectrum at the lowest measured temperature does not show an opening of the superconducting gap, requesting further studies to explore the superconducting properties of the K-doped picene film. The results will be discussed by comparison with previous and recent spectroscopic studies.

    DOI: 10.1088/1361-648X/29/6/064001

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  • Ce 4f electronic states of CeO1-xFxBiS2 studied by soft x-ray photoemission spectroscopy Reviewed

    Wakita, Takanori, Terashima, Kensei, Hamada, Takahiro, Fujiwara, Hirokazu, Minohara, Makoto, Kobayashi, Masaki, Horiba, Koji, Kumigashira, Hiroshi, Kutluk, Galif, Nagao, Masanori, Watauchi, Satoshi, Tanaka, Isao, Demura, Satoshi, Okazaki, Hiroyuki, Takano, Yoshihiko, Mizuguchi, Yoshikazu, Miura, Osuke, Okada, Kozo, Muraoka, Yuji, Yokoya, Takayoshi

    Physical Review B   95 ( 8 )   085109   2017

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    DOI: 10.1103/PhysRevB.95.085109

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  • Determination of the local structure of CsBi4-xPbxTe6 (x=0, 0.5) by X-ray absorption spectroscopy Reviewed

    Takanori Wakita, Eugenio Paris, Takashi Mizokawa, Muammer Yasin Hacisalihoglu, Kensei Terashima, Hiroyuki Okazaki, Olivier Proux, Isabelle Kieffer, Eric Lahera, William Del Net, Luca Olivi, Yoshihiko Takano, Yuji Muraoka, Takayoshi Yokoya, Naurang L. Saini

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   18 ( 36 )   25136 - 25142   2016.9

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:ROYAL SOC CHEMISTRY  

    We have studied the local structure and valence electronic unoccupied states of thermoelectric CsBi4Te6 and superconducting CsBi3.5Pb0.5Te6 (T-c similar to 3 K) by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) measurements. The Bi-L-3 edge EXAFS reveals wide Bi-Te distance distribution for both compounds indicating complex atomic arrangements in the studied system. The mean square relative displacements (MSRDs) of the Bi-Te bond distances appear largely increased in Pb substituted system due to larger overall local disorder, however, one of the Bi-Te bonds shows a reduced disorder. On the other hand, the Bi-L-3 edge XANES is hardly affected by Pb substitution while the Te-L-1 edge XANES reveals increased density of unoccupied Te 5p states. This suggests that the carriers introduced by the Pb substitution in CsBi4-xPbxTe6 preferentially goes on Te sites. Similarly, the Cs-L-3 edge XANES also shows small changes due to Pb-substitution and reduced local disorder indicated by the reduced width of the Cs-L3 edge white line. We have also shown that the X-ray photoemission spectroscopy (XPS) measurements on various electronic core levels are in a qualitative agreement with the XANES results. These findings are consistent with carrier doping and a reduced disorder in one direction to be likely factors to drive the thermoelectric CsBi4Te6 into a bulk superconductor by Pb-substitution in CsBi4-xPbxTe6.

    DOI: 10.1039/c6cp04949d

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  • Observation of a Hidden Hole-Like Band Approaching the Fermi Level in K-Doped Iron Selenide Superconductor Reviewed

    Masanori Sunagawa, Kensei Terashima, Takahiro Hamada, Hirokazu Fujiwara, Tetsushi Fukura, Aya Takeda, Masashi Tanaka, Hiroyuki Takeya, Yoshihiko Takano, Masashi Arita, Kenya Shimada, Hirofumi Namatame, Masaki Taniguchi, Katsuhiro Suzuki, Hidetomo Usui, Kazuhiko Kuroki, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   85 ( 7 )   073704   2016.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:PHYSICAL SOC JAPAN  

    One of the ultimate goals of the study of iron-based superconductors is to identify the common feature that produces the high critical temperature (T-c). In the early days, based on a weak-coupling viewpoint, the nesting between hole-and electron-like Fermi surfaces (FSs) leading to the so-called s +/- state was considered to be one such key feature. However, this theory has faced a serious challenge ever since the discovery of alkali-metal-doped FeSe (AFS) superconductors, in which only electron-like FSs with a nodeless superconducting gap are observed. Several theories have been proposed, but a consistent understanding is yet to be achieved. Here we show experimentally that a hole-like band exists in KxFe2-ySe2, which presumably forms a hole-like Fermi surface. The present study suggests that AFS can be categorized in the same group as iron arsenides with both hole- and electron-like FSs present. This result provides a foundation for a comprehensive understanding of the superconductivity in iron-based superconductors.

    DOI: 10.7566/JPSJ.85.073704

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  • Local electronic state in the half-metallic ferromagnet CrO2 investigated by site-selective Cr-53 NMR measurements Reviewed

    Hikaru Takeda, Yasuhiro Shimizu, Yoshiaki Kobayashi, Masayuki Itoh, Takaaki Jin-no, Masahiko Isobe, Yutaka Ueda, Sho Yoshida, Yuji Muraoka, Takayoshi Yokoya

    PHYSICAL REVIEW B   93 ( 23 )   235129   2016.6

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    We have made Cr-53 NMR measurements on polycrystalline and single-crystalline film samples to study the local electronic state of a half-metallic ferromagnet CrO2 which has the rutile structure with one crystallographically equivalent Cr site. We observe two kinds of Cr-53 NMR spectra in the ferromagnetic state of both the samples. An analysis on the hyperfine field shows the presence of two Cr sites with different orbital occupancies, suggesting that a local orbital order takes place with breaking the local symmetry in the rutile structure. This may be ascribed to the negative charge transfer between chromium and oxygen ions.

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  • Preparation of TaO2 thin films using NbO2 template layers by a pulsed laser deposition technique Reviewed

    Y. Muraoka, Y. Fujimoto, M. Kameoka, Y. Matsuura, M. Sunagawa, K. Terashima, T. Wakita, T. Yokoya

    THIN SOLID FILMS   599   125 - 132   2016.1

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    TaO2 thin films were prepared using rutile-type NbO2 template layers on Al2O3 (0001) substrates by a pulsed laser deposition technique. The structural and electronic properties of the films were characterized by performing four-circle X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) measurements. Four-circle XRD measurements revealed the formation and epitaxial growth of (100)-oriented tetragonal TaO2 on the NbO2 template layers. On the other hand, XPS measurements showed two kinds of valence states, namely Ta4+ and Ta5+ in the surface region of the film. The results from the XRD and XPS measurements suggest that the film is composed of epitaxially grown TaO2 with an amorphous Ta2O5 surface layer. It is found from control experiments that the NbO2 template layers play an important role in inducing the crystallization of the TaO2 films and promoting the formation of Ta4+ in the films deposited thereon. The results indicate the effectiveness of the NbO2 template layers for the formation of TaO2 thin films. Our work presents a promising method for the preparation of TaO2 thin films and provides a starting point for further research on TaO2. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.tsf.2015.12.066

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  • Bulk sensitive angle-resolved photoelectron spectroscopy on Nd(O,F)BiS2 Reviewed

    K. Terashima, J. Sonoyama, M. Sunagawa, H. Fujiwara, T. Nagayama, T. Muro, M. Nagao, S. Watauchi, I. Tanaka, H. Okazaki, Y. Takano, Y. Mizuguchi, H. Usui, K. Suzuki, K. Kuroki, T. Wakita, Y. Muraoka, T. Yokoya

    TMU INTERNATIONAL SYMPOSIUM ON NEW QUANTUM PHASES EMERGING FROM NOVEL CRYSTAL STRUCTURE   683   0012003   2016

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    Bulk electronic structure of novel layered superconductor Nd(O,F)BiS2 was studied by using soft x-ray angle-resolved photoelectron spectroscopy (ARPES). Electron-like Fermi surface centered at the X(R) point was observed, consistent with earlier ARPES reports on surface-sensitive VUV light source. Based on the comparison of the electronic structure between Nd(O,F)BiS2 and La(O,F)BiS2, we discuss possible important factors for the superconductivity in this series of material.

    DOI: 10.1088/1742-6596/683/1/012003

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  • Comparative ARPES studies of LaOxF1-xBiS2 (x=0.23 and 0.46) Reviewed

    K. Terashima, T. Wakita, M. Sunagawa, H. Fujiwara, T. Nagayama, K. Ono, H. Kumigashira, M. Nagao, S. Watauchi, I. Tanaka, H. Okazaki, Y. Takano, Y. Mizuguchi, H. Usui, K. Kuroki, Y. Muraoka, T. Yokoya

    TMU INTERNATIONAL SYMPOSIUM ON NEW QUANTUM PHASES EMERGING FROM NOVEL CRYSTAL STRUCTURE   683   012002   2016

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    BiS2-based layered superconductors are new superconductors, having been paid special attention due to the layered crystal structure and the characteristic electronic structure that can lead to exotic mechanism of superconductivity as well as cooperation of superconductivity and ordered phases. In this article, we report valence band dispersions and Fermi surface topology of LaO1-xFxBiS2 (x = 0.23, T-c < 2 K) studied by angle-resolved photoemission spectroscopy, and compared them with those of LaO1-xFxBiS2 (x = 0.46, T-c = 3.1 K). We discuss experimental x dependent electronic structures and its relation to T-c. We also point to anomalous spectroscopic features in LaO1-xFxBiS2 (x = 0.46) that can be explained by band structure calculations considering distorted lattice, suggesting role of dynamical or static lattice distortion to the physical properties.

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  • Intrinsic spin polarized electronic structure of CrO2 epitaxial film revealed by bulk-sensitive spin-resolved photoemission spectroscopy Reviewed

    Hirokazu Fujiwara, Masanori Sunagawa, Kensei Terashima, Tomoko Kittaka, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

    APPLIED PHYSICS LETTERS   106 ( 20 )   202404   2015.5

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    We have performed bulk-sensitive spin-resolved photoemission spectroscopy in order to clarify the intrinsic spin-resolved electronic states of half-metallic ferromagnet CrO2. We used CrO2 epitaxial films on TiO2(100), which shows a peak at 1 eV with a clear Fermi edge, consistent with the bulk-sensitive PES spectrum for CrO2. In spin-resolved spectra at 40 K, while the Fermi edge was observed in the spin up (majority spin) state, no states at the Fermi level (EF) with an energy gap of 0.5 eV below EF were observed in the spin down (minority spin) state. At 300 K, the gap in the spin down state closes. These results are consistent with resistivity measurements and magnetic hysteresis curves of the fabricated CrO2 film, constituting spectroscopic evidence for the half-metallicity of CrO2 at low temperature and reducing the spin polarization at room temperature. We also discuss the electron correlation effects of Cr 3d. (C) 2015 AIP Publishing LLC.

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  • Comparative ARPES Study on Iron-Platinum-Arsenide Superconductor Ca-10(Pt4As8)(Fe2-xPtxAs2)(5) (x=0.25 and 0.42) Reviewed

    Masanori Sunagawa, Rikiya Yoshida, Toshihiko Ishiga, Koji Tsubota, Taihei Jabuchi, Junki Sonoyama, Satomi Kakiya, Daisuke Mitsuoka, Kazutaka Kudo, Minoru Nohara, Kanta Ono, Hiroshi Kumigashira, Tamio Oguchi, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   84 ( 5 )   055001   2015.5

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    We studied the electronic structure of Ca-10(Pt4As8)(Fe2-xPtxAs2)(5) for two platinum concentrations with different T-c using ARPES. From the carrier number estimated from the areas of FS sheets, we found that the Pt substitution induces electron doping into the Fe2As2 layers (effectively two electrons per Pt atom). In addition, we found that the FS nesting condition in x = 0.25 is stronger than that in x = 0.42, indicating close correlation between the FS nesting and T-c.

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  • Signature of high T-c above 25 K in high quality superconducting diamond Reviewed

    Hiroyuki Okazaki, Takanori Wakita, Takayuki Muro, Tetsuya Nakamura, Yuji Muraoka, Takayoshi Yokoya, Shin-ichiro Kurihara, Hiroshi Kawarada, Tamio Oguchi, Yoshihiko Takano

    APPLIED PHYSICS LETTERS   106 ( 5 )   052601   2015.2

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    We have observed zero resistivity above 10K and an onset of resistivity reduction at 25.2K in a heavily B-doped diamond film. However, the effective carrier concentration is similar to that of superconducting diamond with a lower T-c. We found that the carrier has a longer mean free path and lifetime than in the previous report, indicating that this highest T-c diamond has better crystallinity compared to that of other superconducting diamond films. In addition, the susceptibility shows a small transition above 20K in the high quality diamond, suggesting a signature of superconductivity above 20 K. These results strongly suggest that heavier carrier doped defect-free crystalline diamond could give rise to high T-c diamond. (C) 2015 AIP Publishing LLC.

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  • Signature of high $T_c$ around 25K in higher quality heavily boron-doped diamond Reviewed

    H. Okazaki, T. Wakita, T. Muro, T. Nakamura, Y. Muraoka, T. Yokoya, S. Kurihara, H. Kawarada, T. Oguchi, Y. Takano

    Appl. Phys. Lett.   2015.2

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  • Proximity to Fermi-surface topological change in superconductingLaO0.54F0.46BiS2 Reviewed

    Kensei Terashima, Junki Sonoyama, Takanori Wakita, Masanori Sunagawa, Kanta Ono, Hiroshi Kumigashira, Takayuki Muro, Masanori Nagao, Satoshi Watauchi, Isao Tanaka, Hiroyuki Okazaki, Yoshihiko Takano, Osuke Miura, Yoshikazu Mizuguchi, Hidetomo Usui, Katsuhiro Suzuki, Kazuhiko Kuroki, Yuji Muraoka, Takayoshi Yokoya

    Physical Review B   90 ( 22 )   220512(R)   2014.12

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    The electronic structure of nearly optimally doped novel superconductor LaO1-xFxBiS2(x = 0.46) was investigated using angle-resolved photoemission spectroscopy (ARPES). We clearly observed band dispersions from 2 to 6 eV binding energy and near the Fermi level (E-F), which are well reproduced by first-principles calculations when the spin-orbit coupling is taken into account. The ARPES intensity map near E-F shows a squarelike distribution around the Gamma(Z) point in addition to electronlike Fermi-surface (FS) sheets around the X(R) point, indicating that FS of LaO0.54F0.46BiS2 is in close proximity to the theoretically predicted topological change.

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.90.220512/fulltext

  • Electronic Structures of CeM2Al10 (M = Fe, Ru, and Os) Studied by Soft X-ray Resonant and High-Resolution Photoemission Spectroscopies Reviewed

    Toshihiko Ishiga, Takanori Wakita, Rikiya Yoshida, Hiroyuki Okazaki, Koji Tsubota, Masanori Sunagawa, Kanta Uenaka, Kozo Okada, Hiroshi Kumigashira, Masaharu Oshima, Keisuke Yutani, Yuji Muro, Toshiro Takabatake, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   83 ( 9 )   094717   2014.9

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    We have performed a photoemission spectroscopy (PES) study of CeM2Al10 (M = Fe, Ru, and Os) to directly observe the electronic structure involved in the unusual magnetic ordering. Soft X-ray resonant (SXR) PES provides spectroscopic evidence of the hybridization between conduction and Ce 4f electrons (c-f hybridization) and the order of the hybridization strength (Ru < Os < Fe). High-resolution (HR) PES of CeRu2Al10 and CeOs2Al10, as compared with that of CeFe2Al10, identifies two structures that can be ascribed to structures induced by the c-f hybridization and the antiferromagnetic ordering, respectively. Although the c-f hybridization-induced structure is a depletion of the spectral intensity (pseudogap) around the Fermi level (E-F) with an energy scale of 20-30 meV, the structure related to the antiferromagnetic ordering is observed as a shoulder at approximately 10-11 meV within the pseudogap. The energies of the shoulder structures of CeRu2Al10 and CeOs2Al10 are approximately half of the optical gap (20 meV), indicating that E-F is located at the midpoint of the gap.

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  • Current-Induced Enhancement of Magnetic Anisotropy in Spin-Charge-Coupled Multiferroic YbFe2O4 Reviewed

    Kenji Yoshii, Daiju Matsumura, Hiroyuki Saitoh, Takashi Kambe, Mamoru Fukunaga, Yuji Muraoka, Naoshi Ikeda, Shigeo Mori

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   83 ( 6 )   063708   2014.6

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    We report the change in the magnetic properties of multiferroic YbFe2O4 caused by cooling in the presence of an electrical current. The magnetization measured after the cooling is similar to 10-20% smaller than that after cooling without a current. The current also affects the magnetic anisotropy below similar to 100 K; the magnetic coercivity is increased by similar to 10-20%. These phenomena may arise from the coexistence of ferromagnetic and antiferromagnetic domains or a disturbance in the formation of charge-ordered domains. From the viewpoint of application, the enhancement of anisotropy by an electrical current provides a method for stabilizing magnetization other than the well-known method of exchange bias.

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  • Persistent insulator-to-metal transition of a VO2 thin film induced by soft X-ray irradiation Reviewed

    Yuji Muraoka, Hiroki Nagao, Shinsuke Katayama, Takanori Wakita, Masaaki Hirai, Takayoshi Yokoya, Hiroshi Kumigashira, Masaharu Oshima

    JAPANESE JOURNAL OF APPLIED PHYSICS   53 ( 5 )   05FB09   2014.5

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    We present a persistent soft-X-ray-induced insulator-to-metal transition at room temperature for VO2 thin films. Continuous soft X-ray irradiation renders the insulating electronic state metallic in the VO2 thin films, which has been found by photoemission spectroscopy measurement. The observed transition is irreversible and the metallic state persists when soft X-ray irradiation is stopped. The analysis of valence band spectra reveals that the density of states (DOS) of the V 3d band increases with irradiation time, while the DOS of the O 2p band decreases. We propose a simple model where the persistent insulator-to-metal transition is driven by oxygen desorption from VO2 thin films under soft X-ray irradiation. The present results will help in developing a new route for controlling the phase transition of VO2 by light. (C) 2014 The Japan Society of Applied Physics

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  • Ultrafast photoinduced transition of an insulating VO2 thin film into a nonrutile metallic state Reviewed

    Rikiya Yoshida, Takashi Yamamoto, Yukiaki Ishida, Hiroki Nagao, Tsubasa Otsuka, Kuninari Saeki, Yuji Muraoka, Ritsuko Eguchi, Kyoko Ishizaka, Takayuki Kiss, Shuntaro Watanabe, Teruto Kanai, Jiro Itatani, Shik Shin

    PHYSICAL REVIEW B   89 ( 20 )   205114   2014.5

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    Using time-resolved photoemission spectroscopy, we have investigated the nonequilibrium electronic structures of a VO2 thin film upon photoexcitation. We employed the high-harmonic generation method, which was crucial in obtaining the results. Irradiation by a 170-fs optical pulse at a fluence above similar to 6 mJ/cm(2) rapidly converts the insulating VO2 thin film into a metallic state, and we show that the transition is accompanied by a spectral-weight redistribution over a 1-eV scale. This observation provides direct spectroscopic evidence of an ultrafast insulator-to-metal transition. The transient metallic state has a unique spectrum that deviates from the static spectrum of the rutile metal phase. We also observe an anomalous spreading of spectral weight up to similar to 0.4 eV above the Fermi level as soon as the transient metallic state emerges. The temporal evolution of the spectral weight near the Fermi level exhibits an ultrafast increase and a subsequent slower increase over similar to 3 ps. We suggest that a broadening mechanism related to the excitation of phonon modes is responsible for the spreading of the spectral weight and that the slower increase of the spectral weight is associated with the expansion of the metallic region after photoinduced nucleation. In addition, the initial nucleation of the metallic state appears to be spatially inhomogeneous even near the surface. The results of this study highlight the uniqueness of the nonequilibrium metallic state in comparison to the equilibrium rutile metallic state from an electronic-state perspective.

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  • Characteristic two-dimensional Fermi surface topology of high-T-c iron-based superconductors Reviewed

    Masanori Sunagawa, Toshihiko Ishiga, Koji Tsubota, Taihei Jabuchi, Junki Sonoyama, Keita Iba, Kazutaka Kudo, Minoru Nohara, Kanta Ono, Hiroshi Kumigashira, Tomohiro Matsushita, Masashi Arita, Kenya Shimada, Hirofumi Namatame, Masaki Taniguchi, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

    SCIENTIFIC REPORTS   4   4381   2014.3

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    Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors. Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-T-c). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-T-c materials remains unclear. Here we demonstrate a phase of electron-doped CaFe2As2 (La and P co-doped CaFe2As2) with T-c = 45 K, which is the highest T-c found for the AEFe(2)As(2) bulk superconductors (122-type; AE = Alkaline Earth), possesses only cylindrical hole-and electron-like FSs. This result indicates that FS topology consisting only of two-dimensional sheets is characteristic of both hole-and electron-doped 122-type high-T-c superconductors.

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  • Soft X-ray Photoemission Study of New BiS2-Layered Superconductor LaO1-xFxBiS2 Reviewed

    Shinsuke Nagira, Junki Sonoyama, Takanori Wakita, Masanori Sunagawa, Yudai Izumi, Takayuki Muro, Hiroshi Kumigashira, Masaharu Oshima, Keita Deguchi, Hiroyuki Okazaki, Yoshihiko Takano, Osuke Miura, Yoshikazu Mizuguchi, Katsuhiro Suzuki, Hidetomo Usui, Kazuhiko Kuroki, Kozo Okada, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   83 ( 3 )   033703   2014.3

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    We use core level and valence band soft X-ray photoemission spectroscopy (SXPES) to investigate the electronic structure of new BiS2 layered superconductor LaO1-xFxBiS2. The core level spectra of doped samples show a new spectral feature on the lower binding energy side of the Bi 4 f main peak, which may be explained by core-hole screening with metallic states near the Fermi level (E-F). The experimental electronic structure and its x dependence (a higher binding energy shift of the valence band as well as appearance of new states near E-F having the dominant Bi 6p character) were found to be consistent with the predictions of band structure calculations in general. Noticeable deviation of the spectral shape of the states near EF from that of calculations might provide insight into interesting physical properties. This study provides the first experimental electronic structure of the new BiS2 layered superconductors.

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  • Evidence for metallic states in potassium-intercalated picene film on graphite Reviewed

    Hiroyuki Okazaki, Taihei Jabuchi, Takanori Wakita, Takashi Kato, Yuji Muraoka, Takayoshi Yokoya

    PHYSICAL REVIEW B   88 ( 24 )   245414   2013.12

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    We report the results of photoemission spectroscopy on the potassium concentration (x) dependence of K-x picene films on graphite. The results show a systematic shift of a whole valence band and the appearance of a clear Fermi edge for a certain value of x, with additional structures at higher binding energies. Observed spectral evolutions are reminiscent to those of doped C-60, implying that the K-x picene film has multiple phases depending on the K concentration. Appearance of a clear Fermi edge, in contrast to multilayer K-x picene films on Au, SiO2, and Ag(111) substrates, where no clear Fermi edges are observed, suggests that the emergence of the metallic states for K-x picene films depends on the specific molecular orientations in the films on different substrates.

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  • Collapsed Tetragonal Phase Transition of Ca(Fe1-xRhx)(2)As-2 Studied by Photoemission Spectroscopy Reviewed

    Koji Tsubota, Takanori Wakita, Hiroki Nagao, Chiaki Hiramatsu, Toshihiko Ishiga, Masanori Sunagawa, Kanta Ono, Hiroshi Kumigashira, Masataka Danura, Kazutaka Kudo, Minoru Nohara, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   82 ( 7 )   073705   2013.7

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    We have investigated the changes in the band structure and core-level energy of Ca(Fe1-xRhx)(2)As-2 across the tetragonal-collapsed tetragonal (T-cT) phase transition using photoemission spectroscopy. Angle-resolved photoemission spectroscopy clearly demonstrates that, at the Gamma point in the Brillouin zone, a hole-like band that crosses the Fermi level in the T phase lowers its energy position and is completely filled in the cT phase. This indicates the disappearance of a hole-like Fermi surface around the zone center in the cT phase, which gives rise to the extinction of nesting. The relationship of the present results with the results of previous transport and magnetic studies is discussed. The temperature dependences of the As 3d and Ca 2p core levels show energy shifts toward higher and lower binding energies, respectively. These data constitute the first direct experimental results on electronic structure and chemical states across the T-cT transition.

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  • Spinodal Decomposition in the TiO2-VO2 System Reviewed

    Zenji Hiroi, Hiroaki Hayamizu, Toni Yoshida, Yuji Muraoka, Yoshihiko Okamoto, Jun-ichi Yamaura, Yutaka Ueda

    CHEMISTRY OF MATERIALS   25 ( 11 )   2202 - 2210   2013.6

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    Spinodal decomposition is a ubiquitous phenomenon leading to phase separation from a uniform solution. We show that a spinodal decomposition occurs in a unique combination of two rutile compounds of TiO2 and VO2, which are chemically and physically distinguished from each other: TiO2 is a wide-gap insulator with photocatalytic activities, and VO2 is assumed to be a strongly correlated electron system which exhibits a dramatic metal insulator transition at 342 K. The spinodal decomposition takes place below 830 K at a critical composition of 34 mol % Ti, generates a unidirectional composition modulation along the c axis with a wavelength of approximately 6 nm, and finally results in the formation of self-assembled lamella structures made up of Ti-rich and V-rich layers stacked alternately with 30-50 nm wavelengths. A metal insulator transition is not observed in quenched solid solutions with intermediate compositions but emerges in the thin V-rich layers as the result of phase separation. Interestingly, the metal insulator transition remains as sharp as in pure VO2 even in such thin layers and takes place at significantly reduced temperatures of 310-340 K, which is probably due to a large misfit strain induced by lattice matching at the coherent interface.

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  • Translational Symmetry Breaking and Gapping of Heavy-Quasiparticle Pocket in URu 2 Si 2 Reviewed

    Rikiya Yoshida, Koji Tsubota, Toshihiko Ishiga, Masanori Sunagawa, Jyunki Sonoyama, Dai Aoki, Jacques Flouquet, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

    Scientific Reports   3   2750   2013

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    URu 2 Si 2 is a uranium compound that exhibits a so-called 'hidden-order' transition at ∼17.5â€...K. However, the order parameter of this second-order transition as well as many of its microscopic properties remain unclarified despite considerable research. One of the key questions in this regard concerns the type of spontaneous symmetry breaking occurring at the transition
    although rotational symmetry breaking has been detected, it is not clear whether another type of symmetry breaking also occurs. Another key question concerns the property of Fermi-surface gapping in the momentum space. Here we address these key questions by a momentum-dependent observation of electronic states at the transition employing ultrahigh-resolution three-dimensional angle-resolved photoemission spectroscopy. Our results provide compelling evidence of the spontaneous breaking of the lattice's translational symmetry and particle-hole asymmetric gapping of a heavy quasiparticle pocket at the transition.

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  • Te concentration dependent photoemission and inverse-photoemission study of FeSe1-xTex Reviewed

    Takayoshi Yokoya, Rikiya Yoshida, Yuki Utsumi, Koji Tsubota, Hiroyuki Okazaki, Takanori Wakita, Yoshikazu Mizuguchi, Yoshihiko Takano, Takayuki Muro, Yukako Kato, Hiroshi Kumigashira, Masaharu Oshima, Hisatomo Harima, Yoshihiro Aiura, Hitoshi Sato, Akihiro Ino, Hirofumi Namatame, Masaki Taniguchi, Masaaki Hirai, Yuji Muraoka

    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS   13 ( 5 )   054403   2012.10

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    We have characterized the electronic structure of FeSe1-xTex for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (E-F): its splitting near EF and filling of the pseudogap in FeSe. IPES shows two features, near E-F and approximately 6 eV above E-F; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near E-F for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe.

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  • Comparative photoemission studies on the superconducting gap of the filled skutterudite superconductors LaPt4Ge12 and PrPt4Ge12 Reviewed

    Yoshiaki Nakamura, Hiroyuki Okazaki, Rikiya Yoshida, Takanori Wakita, Hiroyuki Takeya, Kazuto Hirata, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya

    PHYSICAL REVIEW B   86 ( 1 )   014521   2012.7

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    We performed a comparative study of the superconducting gap in the new filled skutterudite superconductors LaPt4Ge12 and PrPt4Ge12 using high-resolution photoemission spectroscopy. We succeeded in observing spectral changes across T-c that reflect the opening of the superconducting gap in both compounds and also in observing a noticeable difference in their respective superconducting spectral shapes near the Fermi level, pointing toward a more complex superconducting gap structure in PrPt4Ge12. In addition, we found that the two-gap model is more suitable for describing the superconducting-state spectrum of PrPt4Ge12 than the single-isotropic-gap and single-anisotropic-gap models, which suggests an explanation that multiband effects may possibly induce the anomalous superconducting properties of PrPt4Ge12.

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  • Observation of two fine structures related to the hidden order in the spectral functions of URu 2Si 2 Reviewed

    Rikiya Yoshida, Masaki Fukui, Yoshinori Haga, Etsuji Yamamoto, Yoshichika Onuki, Mario Okawa, Walid Malaeb, Shik Shin, Yuji Muraoka, Takayoshi Yokoya

    Physical Review B - Condensed Matter and Materials Physics   85 ( 24 )   241102   2012.6

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    We studied the spectral functions of URu 2Si 2 in the hidden-order state by means of ultrahigh-resolution angle-resolved photoemission spectroscopy. High signal-to-noise ratio data uncover the existence of two anomalous fine structures, namely a "splitting" in the previously reported narrow dispersive band, and a small, dispersionless "satellite" structure. These structures can be explained by neither ordinary bands nor the development of a hybridization of two states
    thus our observation should evoke the consideration of complicated many-body effects. As a possible origin, we suggest the existence of electron-mode coupling in the ordered state. © 2012 American Physical Society.

    DOI: 10.1103/PhysRevB.85.241102

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  • Observation of two fine structures related to the hidden order in the spectral functions of URu2Si2 Reviewed

    Rikiya Yoshida, Masaki Fukui, Yoshinori Haga, Etsuji Yamamoto, Yoshichika Onuki, Mario Okawa, Walid Malaeb, Shik Shin, Yuji Muraoka, Takayoshi Yokoya

    PHYSICAL REVIEW B   85 ( 24 )   241102(R)   2012.6

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    We studied the spectral functions of URu2Si2 in the hidden-order state by means of ultrahigh-resolution angle-resolved photoemission spectroscopy. High signal-to-noise ratio data uncover the existence of two anomalous fine structures, namely a "splitting" in the previously reported narrow dispersive band, and a small, dispersionless "satellite" structure. These structures can be explained by neither ordinary bands nor the development of a hybridization of two states; thus our observation should evoke the consideration of complicated many-body effects. As a possible origin, we suggest the existence of electron-mode coupling in the ordered state.

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  • Effectiveness of a hot-filament chemical vapor deposition method for preparation of a boron-doped superconducting diamond film with higher superconducting transition temperature Reviewed

    T. Doi, T. Fukaishi, C. Hiramatsu, T. Wakita, M. Hirai, Y. Muraoka, T. Yokoya, Y. Kato, Y. Izumi, T. Muro, Y. Tamenori

    DIAMOND AND RELATED MATERIALS   25   5 - 7   2012.5

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    We have investigated the effectiveness of a hot-filament chemical vapor deposition (HFCVD) method for preparation of a boron-doped superconducting diamond film with higher superconducting transition temperature (T-c). A boron-doped superconducting diamond film has been fabricated on a diamond (111) substrate using the HFCVD method, and studied by means of scanning electron microscopy. X-ray photoelectron spectroscopy (XPS), and resistivity. The film consists of grains with an average size of 200 mm. Analyses of valence band and boron Is core-level XPS spectra indicate the formation of boron-doped diamond film on the substrate. From the resistivity measurements, the film is found to be a superconductor with onset T-c of 7.1 K. Carrier concentration determined by Hall conductivity measurements is 1.1 x 10(21) cm(-3). The value of T-c is higher compared with that in boron-doped superconducting diamond films prepared by a commonly used microwave plasma-assisted chemical vapor deposition (MPCVD) method, at the same carrier concentration [A. Kawano et al., Phys. Rev. B 82 (2010) 085318]. The result of higher T-c in the film by the HFCVD method is consistent with the previous one [Wang et al., Diamond Relat. Mater. 15 (2006) 659], suggesting that the HFCVD method is effective for preparation of boron-doped superconducting diamond films showing higher T-c. (C) 2012 Elsevier B.V. All rights reserved.

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  • Photoemission Study of Rh17S15 Superconductor Reviewed

    Masaki Fukui, Rikiya Yoshida, Yoshiaki Nakamura, Yukako Kato, Takayuki Muro, Rikio Settai, Yoshichika Onuki, Hisatomo Harima, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   80   SA111   2011.7

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    We have investigated the electronic structures of Rh17S15 by using soft x-ray photoemission spectroscopy and first principle band structure calculations. While S 2p core level spectra are explained by symmetric components, Rh 3d core level exhibits asymmetric line shape, suggesting a dominant Rh 4d character at the states near the Fermi level. The binding energy of Rh 4d in Rh17S15 is similar to the one in Rh metal, and this observation implies metallic Rh-Rh bonding. Many features in experimental valence spectra are reasonably described by the calculations, indicating that one particle approximation is a good starting point to understand the electronic properties of Rh17S15. The comparison between the experiment and the calculation suggests that Rh 4d character at the states near the Fermi level is essential for the correlated superconductivity in Rh17S15. However, some deviation between the experiment and the calculation as well as a finite mass enhancement are found, indicating some corrections on the treatment of electron-phonon coupling and/or electron correlations are necessary.

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  • Photoemission study of electronic structure evolution across the metal-insulator transition of heavily B-doped diamond Reviewed

    H. Okazaki, T. Arakane, K. Sugawara, T. Sato, T. Takahashi, T. Wakita, M. Hirai, Y. Muraoka, Y. Takano, S. Ishii, S. Iriyama, H. Kawarada, T. Yokoya

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   72 ( 5 )   582 - 584   2011.5

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    We studied the electronic structure evolution of heavily B-doped diamond films across the metal-insulator transition (MIT) using ultraviolet photoemission spectroscopy (UPS). From high-temperature UPS, through which electronic states near the Fermi level (E(F)) up to similar to 5k(B)T can be observed (k(B) is the Boltzmann constant and T the temperature), we observed the carrier concentration dependence of spectral shapes near E(F). Using another carrier concentration dependent UPS, we found that the change in energy position of sp-band of the diamond valence band, which corresponds to the shift of E(F), can be explained by the degenerate semiconductor model, indicating that the diamond valence band is responsible for the metallic states for samples with concentrations above MIT. We discuss a possible electronic structure evolution across MIT. (C) 2010 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jpcs.2010.10.052

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  • Ultrahigh-resolution laser photoemission study of URu2Si2 across the hidden-order transition Reviewed

    Rikiya Yoshida, Yoshiaki Nakamura, Masaki Fukui, Yoshinori Haga, Etsuji Yamamoto, Yoshichika Onuki, Mario Okawa, Shik Shin, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   72 ( 5 )   580 - 581   2011.5

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    We have studied the electronic structures of URu2Si2 employing ultrahigh-resolution laser angle-resolved photoemission spectroscopy. The change of photoemission spectra is investigated across the hidden-order transition, and the emergence of a narrow band is clearly observed near the Fermi level for both (pi,0) and (pi,pi) directions. In addition, it is shown that tuning of light's polarization allows the signal of a hole-like dispersive feature to enhance. These observations prove that laser angle-resolved photoemission spectroscopy is an effective tool for studying the evolution of electronic structures across the hidden-order transition in URu2Si2. (C) 2010 Elsevier Ltd. All rights reserved.

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  • Spectroscopic evidence of the formation of (V,Ti)O-2 solid solution in VO2 thinner films grown on TiO2(001) substrates Reviewed

    Y. Muraoka, K. Saeki, R. Eguchi, T. Wakita, M. Hirai, T. Yokoya, S. Shin

    JOURNAL OF APPLIED PHYSICS   109 ( 4 )   043702   2011.2

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    We have prepared VO2 thin films epitaxially grown on TiO2(001) substrates with thickness systematically varied from 2.5 to 13 nm using a pulsed laser deposition method, and studied the transport property and electronic states of the films by means of resistivity and in situ synchrotron photoemission spectroscopy (SRPES). In resistivity measurements, the 13-nm-thick film exhibits a metal-insulator transition at around 290 K on cooling with change of three orders of magnitudes in resistivity. As the film thickness decreases, the metal-insulator transition broadens and the transition temperature increases. Below 4 nm, the films do not show the transition and become insulators. In situ SRPES measurements of near the Fermi level valence band find that the electronic state of the 2.5-nm-thick film is different than that of the temperature-induced insulator phase of VO2 itself although these two states are insulating. Ti 2p core-level photoemission measurements reveal that Ti ions exist near the interface between the films and TiO2 substrates, with a chemical state similar to that in (V,Ti)O-2 solid solution. These results indicate that insulating (V,Ti)O-2 solid solution is formed in the thinner films. We propose a simple growth model of a VO2 thin film on a TiO2(001) substrate. Near the interface, insulating (V,Ti) O-2 solid solution is formed due to the diffusion of Ti ions from the TiO2 substrate into the VO2 film. The concentration of Ti in (V,Ti) O-2 is relatively high near the interface and decreases toward the surface of the film. Beyond a certain film thickness (about 7 nm in the case of the present 13-nm-thick film), the VO2 thin film without any Ti ions starts to grow. Our work suggests that developing a technique for preparing the sharp interface between the VO2 thin films and TiO2 substrates is a key issue to study the physical property of an ultrathin film of "pure" VO2, especially to examine the presence of the novel electronic state called a semi-Dirac point phase predicted by calculations. (c) 2011 American Institute of Physics. [doi:10.1063/1.3549835]

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  • Multiple phosphorus chemical sites in heavily phosphorus-doped diamond Reviewed

    Hiroyuki Okazaki, Rikiya Yoshida, Takayuki Muro, Tetsuya Nakamura, Takanori Wakita, Yuji Muraoka, Masaaki Hirai, Hiromitsu Kato, Satoshi Yamasaki, Yoshihiko Takano, Satoshi Ishii, Tamio Oguchi, Takayoshi Yokoya

    APPLIED PHYSICS LETTERS   98 ( 8 )   082107   2011.2

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    We have performed high-resolution core level photoemission spectroscopy on a heavily phosphorus (P)-doped diamond film in order to elucidate the chemical sites of doped-phosphorus atoms in diamond. P 2p core level study shows two bulk components, providing spectroscopic evidence for multiple chemical sites of doped-phosphorus atoms. This indicates that only a part of doped-phosphorus atoms contribute to the formation of carriers. From a comparison with band calculations, possible origins for the chemical sites are discussed. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3554699]

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  • Electronic structure of U(Ru1-xRhx)(2)Si-2 studied by laser angle-resolved photoemission spectroscopy Reviewed

    R. Yoshida, Y. Nakamura, M. Fukui, Y. Haga, E. Yamamoto, Y. Onuki, M. Okawa, S. Shin, M. Hirai, Y. Muraoka, T. Yokoya

    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2010)   273   012021   2011

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    We have studied electronic structures of U(Ru1-xRhx)(2)Si-2 employing ultrahigh-resolution laser angle-resolved photoemission spectroscopy to understand the effect of Rh substitution. A hole-like dispersive feature, which presumably has Rh d-band character, was observed in U(Ru1-xRhx)(2)Si-2 for both x = 0 and x = 0.03. However, although a heavy quasiparticle band appears in the hidden-order state of URu2Si2 (x = 0), it was not observed for x = 0.03 over the temperature range studied. In addition, it was found that energy-distribution curves at the Fermi vector of the hole-like band for x = 0.03 behave similarly to the Fermi-Dirac function. We also present the mapping of Fermi surfaces formed by the hole-like band, which stay nearly unaffected by Rh substitution.

    DOI: 10.1088/1742-6596/273/1/012021

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  • Synthesis and physical properties of the hollandite-type titanium oxide KxTi8O16 Reviewed

    Yuji Muraoka, Kengo Noami, Takanori Wakita, Masaaki Hirai, Takayoshi Yokoya, Yukako Kayo, Takayuki Muro, Yusuke Tamenori

    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 2   8 ( 2 )   555 - 557   2011

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    Polycrystalline sample of hollandite-type titanium oxide KxTi8O16 has been prepared and studied by magnetization and X-ray photoelectron spectroscopy (XPS). Room temperature ferromagnetic behaviour is observed in the magnetic hysteresis measurements. XPS measurements of the Ti 2p(3/2) core-level finds that the titanium ions take a mixed valence of Ti4+ and Ti3+. In addition, the valence band spectrum reveals that the 3d electrons tend to localize on Ti3+ ions in the hollandite-type TiO2 lattice. Also, analysis of the valence band spectrum shows that the prepared sample is a wide-gap oxide with a band gap of 3.6 eV. These results indicate that the present hollandite-type KxTi8O16 sample can be classified as a TiO2-based wide-gap semiconductor with Curie temperature above room temperature. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

    DOI: 10.1002/pssc.201000383

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  • Photoemission study of Ca-intercalated graphite superconductor CaC6 Reviewed

    Hiroyuki Okazaki, Rikiya Yoshida, Keisuke Iwai, Kengo Noami, Takayuki Muro, Tetsuya Nakamura, Takanori Wakita, Yuji Muraoka, Masaaki Hirai, Fumiaki Tomioka, Yoshihiko Takano, Asami Takenaka, Masahiro Toyoda, Tamio Oguch, Takayoshi Yokoya

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   470   S637 - S638   2010.12

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    In this work, we have performed resonant photoemission studies of Ca-intercalated graphite superconductor CaC6. Using photon energy of the Ca 2p-3d threshold, the photoemission intensity of the peak at Fermi energy (E-F) is resonantly enhanced. This result provides spectroscopic evidence for the existence of Ca 3d states at E-F, and strongly supports that Ca 3d state plays a crucial role for the superconductivity of this material with relatively high T-c. (C) 2009 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physc.2009.10.039

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  • Angle-resolved photoemission study of Si electronic structure: Boron concentration dependence Reviewed

    Takanori Wakita, Hiroyuki Okazaki, Yoshihiko Takano, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   470   S641 - S643   2010.12

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    The boron concentration dependence of the Si electronic structure of Si(1 00)2 x 1 surfaces were investigated by angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra exhibit rigid shifts toward lower binding energy as the boron concentration increases. The band dispersion was obtained from fitting procedure, and it is found that the top of the valence band does not exceed the Fermi level even with a boron concentration 35 times larger than the critical concentration of the metal-insulator transition. (C) 2009 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physc.2009.11.028

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  • Analysis on photoemission spectrum of superconducting FeSe Reviewed

    Rikiya Yoshida, Takanori Wakita, Hiroyuki Okazaki, Yoshikazu Mizuguchi, Shunsuke Tsuda, Yoshihiko Takano, Hiroyuki Takeya, Kazuto Hirata, Yukako Kato, Takayuki Muro, Mario Okawa, Kyoko Ishizaka, Shik Shin, Hisatomo Harima, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   470   S389 - S390   2010.12

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    In this paper, we present the result of soft X-ray photoemission spectroscopy and its comparison with the density functional calculation. Although local density approximation seems to be a good starting point for describing the electronic structure of FeSe, the simulated spectrum poorly reproduced the structure around E-B = 2 eV. This result suggests the necessity of theoretical treatment beyond local density approximation. (C) 2009 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physc.2009.11.172

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  • Electronic Structure of the Novel Filled Skutterudite PrPt4Ge12 Superconductor Reviewed

    Yoshiaki Nakamura, Hiroyuki Okazaki, Rikiya Yoshida, Takanori Wakita, Masaaki Hirai, Yuji Muraoka, Hiroyuki Takeya, Kazuto Hirata, Hiroshi Kumigashira, Masaharu Oshima, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   79 ( 12 )   124701   2010.12

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    We have performed soft x-ray photoemission spectroscopy (SXPES) and resonant photoemission spectroscopy (RPES) of the filled skutterudite superconductor PrPt4Ge12 in order to study the electronic structure of valence band and the character of Pr 4f. SXPES of PrPt4Ge12 measured with 1200 eV photon energy, where spectral contribution of Pr 4f is negligible, was found nearly identical with that of LaPt4Ge12, indicating similarity of Pt-Ge derived electronic states of the two compounds. Good correspondence with band calculations allows us to ascribe the dominant Ge 4p character of the density of states at the Fermi level (E-F). Pr 3d -> 4f RPES shows that, although Pr 4f electrons in PrPt4Ge12 are not as strongly hybridized with conduction electrons near E-F as in PrFe4P12, there are finite Pr 4f contribution to the states near E-F in PrPt4Ge12. These PES results give the information of fundamental electronic structure for understanding the physical properties of the novel filled skutterudite superconductor PrPt4Ge12

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  • Electronic structure of pristine and K-doped solid picene: Nonrigid band change and its implication for electron-intramolecular-vibration interaction Reviewed

    H. Okazaki, T. Wakita, T. Muro, Y. Kaji, X. Lee, H. Mitamura, N. Kawasaki, Y. Kubozono, Y. Yamanari, T. Kambe, T. Kato, M. Hirai, Y. Muraoka, T. Yokoya

    PHYSICAL REVIEW B   82 ( 19 )   195114   2010.11

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    We use photoemission spectroscopy to study electronic structures of pristine and K-doped solid picene. The valence band spectrum of pristine picene consists of three main features with no state at the Fermi level (E(F)) while that of K-doped picene has three structures similar to those of pristine picene with new states near E(F), consistent with the semiconductor-metal transition. The K-induced change cannot be explained with a simple rigid-band model of pristine picene but can be interpreted by molecular-orbital calculations considering electron-intramolecular-vibration interaction. Excellent agreement of the K-doped spectrum with the calculations points to importance of electron-intramolecular-vibration interaction in K-doped picene.

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  • Signature of hidden order and evidence for periodicity modification in URu2Si2 Reviewed

    Rikiya Yoshida, Yoshiaki Nakamura, Masaki Fukui, Yoshinori Haga, Etsuji Yamamoto, Yoshichika Onuki, Mario Okawa, Shik Shin, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya

    PHYSICAL REVIEW B   82 ( 20 )   205108   2010.11

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    The detail of electronic structures near the Fermi level in URu2Si2 has been investigated employing state-of-art laser angle-resolved photoemission spectroscopy. The observation of a narrow dispersive band near the Fermi level in the ordered state as well as its absence in a Rh-substituted sample strongly suggest that the emergence of the narrow band is a clear signature of the hidden-order transition. The temperature dependence of the narrow band, which appears at the onset of the hidden-order transition, invokes the occurrence of periodicity modification in the ordered state, which is shown for the first time by any spectroscopic probe. We compare our data to other previous studies and discuss possible implications.

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  • Bulk and surface physical properties of a CrO(2) thin film prepared from a Cr(8)O(21) precursor Reviewed

    K. Iwai, Y. Muraoka, T. Wakita, M. Hirai, T. Yokoya, Y. Kato, T. Muro, Y. Tamenori

    JOURNAL OF APPLIED PHYSICS   108 ( 4 )   043916   2010.8

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    We have prepared a CrO(2) thin film by chemical vapor deposition from a Cr(8)O(21) precursor and studied the bulk and surface physical properties. The CrO(2) thin film is grown on a TiO(2) (100) substrate by heating of a Cr(8)O(21) precursor and TiO(2) (100) substrate together in a sealed quartz tube. The prepared film is found from x-ray diffraction analysis to be an (100)-oriented single phase. The magnetization and resistivity measurements indicate that the film is a ferromagnetic metal with a Curie temperature of about 400 K. Cr 3s core-level and valence band photoelectron spectroscopy spectra reveal the presence of a metallic CrO(2) in the surface region of the film. Our work indicates that preparation from a Cr(8)O(21) precursor is promising for obtaining a CrO(2) thin film with the metallic surface. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3471811]

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  • Angle-resolved photoemission spectroscopy for VO2 thin films grown on TiO2 (001) substrates Reviewed

    Y. Muraoka, K. Saeki, Y. Yao, T. Wakita, M. Hirai, T. Yokoya, R. Eguchi, S. Shin

    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA   181 ( 2-3 )   249 - 251   2010.8

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    We present the results of angle-resolved photoemission spectroscopy (ARPES) measurements of metallic VO2 thin films. The VO2 thin films have been grown on TiO2 (0 0 1) single crystal substrates using pulsed laser deposition. The films exhibit a first-order metal-insulator transition (MIT) at 305K. In the ARPES spectra of the metallic phase for the films, the O 2p band shows highly dispersive feature in the binding energy range of 3-8 eV along the Gamma-Z direction. The periodicity of the dispersive band is found to be 2.2 A(-1) which is almost identical with the periodicity expected from the c-axis length of the VO2 thin films. The overall feature of the experimental band structure is similar to the band structure calculations. supporting that we have succeeded in observing the dispersive band of the O 2p state in the metallic VO2 thin film. The present work indicates that the ARPES measurements using epitaxial thin films are promising for determining the band structure of VO2. (C) 2010 Elsevier B.V. All rights reserved.

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  • Room temperature ferromagnetic behavior in the hollandite-type titanium oxide Reviewed

    K. Noami, Y. Muraoka, T. Wakita, M. Hirai, Y. Kato, T. Muro, Y. Tamenori, T. Yokoya

    JOURNAL OF APPLIED PHYSICS   107 ( 7 )   073910   2010.4

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    A hollandite-type K(x)Ti(8)O(16) polycrystalline sample has been prepared and studied by magnetization, resistivity and x-ray photoelectron spectroscopy (XPS). Room temperature ferromagnetic behavior is observed in the magnetic hysteresis measurement. The sample shows a semiconductive temperature dependence in the resistivity measurement. Analysis of the Ti 2p(3/2) core-level XPS spectrum indicates that the titanium ions have a mixed valence of Ti(4+) and Ti(3+). In addition, the valence band spectrum reveals that the 3d electrons tend to localize on Ti(3+) ions in the hollandite-type TiO(2) lattice. Also, analysis of the valence band spectrum shows that the prepared sample is a wide-gap oxide with a band gap of 3.6 eV. These results indicate that the present hollandite-type K(x)Ti(8)O(16) sample can be classified as a TiO(2)-based wide-gap semiconductor with Curie temperature above room temperature. Room temperature ferromagnetism (RTFM) decreases in the sample prepared under a strong reducing gas atmosphere, accompanied with the decrease in the resistivity. The results imply that the localized 3d electrons are responsible for the RTFM of the K(x)Ti(8)O(16) sample. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3369500]

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  • Study of electronic states for V thin films deposited on 6H-SiC substrates by soft X-ray emission spectroscopy Reviewed

    M. Hirai, H. Okazaki, R. Yoshida, M. Tajima, K. Saeki, Y. Muraoka, T. Yokoya

    APPLIED SURFACE SCIENCE   256 ( 4 )   948 - 949   2009.11

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    Silicon carbide (SiC) is a candidate material for electronic devices to operate upon crucial environment. Electronic states of silicides and/or carbide/graphite formed in metal/SiC contact system is fundamentally important from the view point of device performance.
    We study interface electronic structure of vanadium (V) thin-film deposited on 6H-SiC(0 0 0 1) Si-face by using a soft X-ray emission spectroscopy (SXES). For specimens of V(38 nm)/6H-SiC (substrate) contact systems annealed at 850 degrees C, the Si L(2,3) emission spectra indicate different shapes and peak energies from the substrate. The product of materials such as silicides and/or ternary materials is suggested. Similarly, the C K alpha emission spectra show the shape and peak energy characteristic of vanadium carbide including substrate 6H-SiC signal. (C) 2009 Elsevier B.V. All rights reserved.

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  • Band dispersion near the Fermi level for VO2 thin films grown on TiO2 (001) substrates Reviewed

    K. Saeki, T. Wakita, Y. Muraoka, M. Hirai, T. Yokoya, R. Eguchi, S. Shin

    PHYSICAL REVIEW B   80 ( 12 )   125406   2009.9

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    We have performed angle-resolved photoemission spectroscopy (ARPES) measurements of VO2 using epitaxial thin films and observed the band dispersion near the Fermi level (E-F) for this compound. The VO2 thin films have been grown on TiO2 (001) single-crystal substrates using pulsed laser deposition. The films exhibit a first-order metal-insulator transition (MIT) at 305 K. In the ARPES spectra of the metallic phase for the films, the O 2p band shows highly dispersive features in the binding-energy range of 3-8 eV along the Gamma-Z direction. Also, the V 3d state shows two dispersive bands around the Gamma point near E-F, indicative of two electron pockets centered at the Gamma point. Both electron pockets have an occupied bandwidth of about 0.4 eV. Assuming the parabolic energy bands around the Gamma point, the effective-mass ratios of the two electron pockets are estimated to be about 0.2 and 1. The present work indicates that the ARPES measurements using epitaxial thin films are promising for determining the band structure of VO2 and thus would play a crucial role to elucidate the mechanism of the MIT in VO2.

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  • The electronic structure of Ca-intercalated superconducting graphite CaC6 Reviewed

    H. Okazaki, R. Yoshida, K. Iwai, K. Noami, T. Muro, T. Nakamura, T. Wakita, Y. Muraoka, M. Hirai, F. Tomioka, Y. Takano, A. Takenaka, M. Toyoda, T. Oguchi, T. Yokoya

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   469 ( 15-20 )   1041 - 1044   2009.8

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    We have measured Ca-intercalated graphite superconductor CaC6 (T-c = 11.2 K) by soft X-ray photoemission spectroscopy in order to understand the electronic structure. For the valence band, we observed several structures that correspond to those of calculated density of states with the partial density of states of Ca 3d at the Fermi level (E-F). We also observed core level spectra that are a very large asymmetric Ca 2p and asymmetric C 1s for CaC6, suggesting the existence of conduction electrons derived from Ca 3d and a charge transfer from Ca to graphene layer. These results provide spectroscopic evidence for PDOS of Ca 3d at E-F. From a comparison of electronic structure of CaC6 and other graphite intercalation compounds (GICs), we found the difference between CaC6 and other superconducting GICs, which provides deeper understanding of the superconductivity of CaC6. (C) 2009 Elsevier B.V. All rights reserved.

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  • Bulk-sensitive spectroscopic studies on noncentrosymmetric superconducting system of Mg-Ir-B Reviewed

    R. Yoshida, H. Okazaki, K. Iwai, K. Noami, T. Muro, M. Okawa, K. Ishizaka, S. Shin, Z. Li, J. L. Luo, G. -Q. Zheng, T. Oguchi, M. Hirai, Y. Muraoka, T. Yokoya

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   469 ( 15-20 )   1034 - 1036   2009.8

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    We present the data from ultrahigh-resolution laser-excited photoemission spectroscopy on a newly discovered noncentrosymmetric superconcluctor Mg(10)Ir(19)B(16). We observed the evidences for the opening of superconducting gap where numerical fittings show that isotropic s-wave model can satisfactorily explain the behavior of spectra near the Fermi level. We also present the valence band photoemission spectrum and B K fluorescence spectrum to discuss the basic electronic structure of Mg(10)Ir(19)B(16). (C) 2009 Elsevier B.V. All rights reserved.

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  • Spectroscopic evidence of the existence of substantial Ca 3d derived states at the Fermi level in the Ca-intercalated graphite superconductor CaC6 Reviewed

    H. Okazaki, R. Yoshida, K. Iwai, K. Noami, T. Muro, T. Nakamura, T. Wakita, Y. Muraoka, M. Hirai, F. Tomioka, Y. Takano, A. Takenaka, M. Toyoda, T. Oguchi, T. Yokoya

    PHYSICAL REVIEW B   80 ( 3 )   035420   2009.7

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    We have performed soft x-ray photoemission studies of Ca-intercalated graphite superconductor CaC6 (T-c=11.2 K). The valence-band spectrum shows six main structures, with a peak at the Fermi level (E-F), which correspond to those of calculated DOS. The intensity of the E-F peak is resonantly enhanced at the Ca 2p-3d threshold, providing spectroscopic evidence for the existence of Ca 3d electrons at E-F, which is confirmed experimentally for the first time. The Ca 2p core-level spectrum has a very large asymmetric line shape, which is further possible suggestion of the existence of Ca 3d derived conduction electrons at Ca sites. These results strongly support the picture where Ca 3d derived interlayer band plays a crucial role for the superconductivity of this material with relatively high T-c.

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  • Photoinduced conductivity in tin dioxide thin films Reviewed

    Y. Muraoka, N. Takubo, Z. Hiroi

    JOURNAL OF APPLIED PHYSICS   105 ( 10 )   103702   2009.5

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    The effects of ultraviolet light irradiation on the conducting properties of SnO(2-x) thin films grown epitaxially on TiO(2) or Al(2)O(3) single-crystal substrates are studied at room temperature. A large increase in conductivity by two to four orders of magnitude is observed with light irradiation in an inert atmosphere and remains after the light is removed. The high-conducting state reverts to the original low-conducting state by exposing it to oxygen gas. These reversible phenomena are ascribed to the desorption and adsorption of negatively charged oxygen species at the grain boundaries, which critically change the mobility of electron carriers already present inside grains by changing the potential barrier height at the grain boundary. The UV light irradiation provides us with an easy and useful route to achieve a high-conducting state even at low carrier density in transparent conducting oxides and also to draw an invisible conducting wire or a specific pattern on an insulating film.

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  • Conductivity Switching by Ultraviolet Light in Tin Dioxide Thin Films Reviewed

    Naoko Takubo, Yuji Muraoka, Zenji Hiroi

    APPLIED PHYSICS EXPRESS   2 ( 4 )   045501   2009.4

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    The effects of ultraviolet (UV) light irradiation on the conducting properties of SnO(2-x) films are studied at room temperature (RT). Large enhancements in conductivity up to 4 orders of magnitude are observed in vacuum for almost insulating films containing small amounts of oxygen vacancies. It is ascribed to the desorption of negatively-charged oxygen species from the grain boundary, which dramatically enhances the mobility of electron carriers already present in the grains through the reduction of potential barriers at the boundary. The low-resistive state induced by light irradiation recovers to the original insulating state by exposing oxygen gas at FIT. (C) 2009 The Japan Society of Applied Physics

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  • Electronic Structure of Superconducting FeSe Studied by High-Resolution Photoemission Spectroscopy Reviewed

    Rikiya Yoshida, Takanori Wakita, Hiroyuki Okazaki, Yoshikazu Mizuguchi, Shunsuke Tsuda, Yoshihiko Takano, Hiroyuki Takeya, Kazuto Hirata, Takayuki Muro, Mario Okawa, Kyoko Ishizaka, Shik Shin, Hisatomo Harima, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   78 ( 3 )   034708   2009.3

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    We have pet-formed soft x-ray and Ultralligh-resolution laser-excited photoemission measurements on tetragonal FeSe, which was recently identified as a superconductor. Energy dependent study of valence band is compared to band Structure Calculations and yields a reasonable assignment of partial densities of states. However, the sharp peak near the Fermi level slightly deviates from the calculated energy position, giving rise to the necessity of self energy correction. We have also performed ultrahigh-resolution laser photoemission experiment on FeSe and observed the suppression of intensity around the Fermi level upon cooling.

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  • Superconducting Gap and Valence Band of Mg10Ir19B16 Studied by Laser and Synchrotron Photoemission Spectroscopy Reviewed

    Rikiya Yoshida, Hiroyuki Okazaki, Keisuke Iwai, Kengo Noami, Takayuki Muro, Mario Okawa, Kyoko Ishizaka, Shik Shin, Zheng Li, Jianlin Luo, Guo-qing Zheng, Tamio Oguchi, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   78 ( 3 )   034705   2009.3

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    We report the results of first photoemission spectroscopy on a newly discovered noncentrosymmetric superconductor Mg10Ir19B16. We measured the valence band structure of Mg10Ir19B16 using soft X-ray photoemission technique and found that the first principal calculation explains our observation well. In the bulk-sensitive laser-excited photoemission study, we observed that the intensity at the Fermi level decreases as we lower the sample temperature, indicative of the opening of superconducting energy gap. Using Dynes' function, we performed fitting analysis on the spectra of superconducting state.

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  • Soft X-ray Core-Level Photoemission Study of Boron Sites in Heavily Boron-Doped Diamond Films Reviewed

    Hiroyuki Okazaki, Rikiya Yoshida, Takayuki Muro, Takanori Wakita, Masaaki Hirai, Yuji Muraoka, Yoshihiko Takano, Shingo Iriyama, Hiroshi Kawarada, Tamio Oguchi, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   78 ( 3 )   034703   2009.3

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    We have performed high-resolution soft x-ray B 1s core-level photoemission spectroscopy of heavily boron-doped diamond films in order to study the chemical sites of doped-boron atoms and their relation to the superconducting transition temperature (T-c). We find that B 1s core-level spectra exhibit several fine structures and three bulk components can he resolved from photon energy dependent studies and spectral fittings. These results indicate existence of several chemical environments of doped-boron atoms. One of the bulk components having the lowest binding energy can be assigned to a signal from substitutionally doped-boron atoms. Comparisons of bulk components with T-c suggest spectroscopic evidence for the importance of substitutionally doped-boron atoms for effective carrier and superconductivity.

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  • Effect of UV light irradiation in SnO2 thin film Reviewed

    Naoko Takubo, Yuji Muraoka, Zenji Hiroi

    LXIII YAMADA CONFERENCE ON PHOTO-INDUCED PHASE TRANSITION AND COOPERATIVE PHENOMENA (PIPT3)   148   012025   2009

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    We observed a drastic increase in conductivity up to three orders of magnitude as a result of a photo-induced effect at the surface in a tin dioxide (SnO2) thin film. The oxygen-atmosphere effect and the light-intensity dependence of conductivity change were also experimentally studied. The experimental results indicate that the conductivity increase was caused by photo-induced oxygen desorption at the surface of the thin film.

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  • Fully gapped superconductivity and strong electron correlations in the beta-pyrochlore KOS2O6 Reviewed

    Y. Kasahara, Y. Shimono, T. Kato, K. Hashimoto, T. Shibauchi, Y. Matsuda, S. Yonezawa, Y. Muraoka, J. Yamaura, Y. Nagao, Z. Hiroi

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   69 ( 12 )   3228 - 3231   2008.12

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    To elucidate the superconducting gap structure and the influence of rattling motion on quasiparticle dynamics in the superconducting state of KOS2O6, thermal conductivity and microwave surface impedance were measured at low temperatures. The magnetic field dependence of thermal conductivity at the lowest temperature and the temperature dependence of penetration depth strongly indicate a fully gapped superconductivity in KOs2O6. The quasiparticle scattering time is strongly enhanced in the superconducting state, indicating a strong electron-electron inelastic scattering in the normal state. These results highlight that KOS2O6 is unique among superconductors, which is characterized by the coexistence of fully gapped superconductivity and strong electron correlations. (C) 2008 Elsevier Ltd. All rights reserved.

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  • Electronic Structure of Noncentrosymmetric Superconductor Li-2(PdxPt1-x)(3)B Studied by Photoemission Spectroscopy Reviewed

    Rikiya Yoshida, Hiroyuki Okazaki, Mitsutoshi Tajima, Takayuki Muro, Izumi Hase, Kozo Okada, Hiroyuki Takeya, Kazuto Hirata, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   77 ( 10 )   104701   2008.10

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    We have performed x-ray photoemission spectroscopy on the system of noncentrosymmetric Superconductor, Li-2(PdxPt1-x)(3)B. For Li2Pt3B, we found two major peaks with two other weak components, and the band calculations were in agreement with the observation. The assignment of valence band features using the calculated partial density of states determined that Pt 5d and B 2p contribute to the density of states at the Fermi level. The effect of antisymmetric spin-orbit coupling on the band Structure might have been probed. and the analysis on the effect of Pt incorporation into the system indicates the smooth evolution of electronic structures. We presented the measurements of core levels (Pd 3d, Pt 4f, and B 1s) and discussed the chemical bonding states and electronic structures from them.

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  • Photoemission evidence for a Mott-Hubbard metal-insulator transition in VO(2) Reviewed

    R. Eguchi, M. Taguchi, M. Matsunami, K. Horiba, K. Yamamoto, Y. Ishida, A. Chainani, Y. Takata, M. Yabashi, D. Miwa, Y. Nishino, K. Tamasaku, T. Ishikawa, Y. Senba, H. Ohashi, Y. Muraoka, Z. Hiroi, S. Shin

    PHYSICAL REVIEW B   78 ( 7 )   075115   2008.8

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    The temperature (T)-dependent metal-insulator transition (MIT) in VO(2) is investigated using bulk sensitive hard-x-ray (similar to 8 keV) valence-band, core-level, and V 2p-3d resonant photoemission spectroscopies (PESs). The valence-band and core-level spectra are compared with full-multiplet cluster model calculations including a coherent screening channel. Across the MIT, V 3d spectral weight transfer from the coherent (3d(1)(C) under bar final) states at Fermi level to the incoherent (3d(0)+3d(1)(L) under bar final) states, corresponding to the lower Hubbard band, leads to gap formation. The spectral shape changes in V 1s and V 2p core levels as well as the valence band are nicely reproduced from cluster model calculations, providing electronic structure parameters. Resonant PES finds that the 3d(1)(L) under bar states resonate across the V 2p-3d threshold in addition to the 3d(0) and 3d(1)(C) under bar states. The results support a Mott-Hubbard transition picture for the first-order MIT in VO(2).

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  • Preparation and characterization of epitaxial Fe(2-x)Ti(x)O(3) films with various Ti concentrations (0.5 < x < 1.0) Reviewed

    Takada M. Nakanishi, T. Fujii, J. Takada, Y. Muraoka

    JOURNAL OF APPLIED PHYSICS   104 ( 3 )   033713   2008.8

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    An ilmenite-hematite solid solution (Fe(2-x)Ti(x)O(3)) is one of the candidates for practical magnetic semiconductors with a high Curie temperature. We have prepared well-crystallized epitaxial Fe(2-x)Ti(x)O(3) films with a wide range of Ti concentrations-x=0.50, 0.60, 0.65, 0.76, 0.87, and 0.94-on alpha-Al(2)O(3)(001) substrates. The films are prepared by a reactive helicon plasma sputtering technique to evaporate Fe and TiO targets simultaneously under optimized oxygen pressure conditions. The structural characterizations of the films reveal that all films have a single phase of the ordered structure with R3 symmetry, where Ti-rich and Fe-rich layers are stacked alternately along the c axis. All films have large ferrimagnetic moments at low temperature, and room temperature magnetization is clearly observed at x < 0.7. The inverse temperature dependence of the resistivities of the films indicates their semiconducting behavior. The film resistivities decrease with decreasing Ti concentration. (c) 2008 American Institute of Physics.

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  • Full-gap superconductivity with strong electron correlations in the beta-pyrochlore KOs2O6 Reviewed

    Y. Kasahara, Y. Shimono, T. Kato, K. Hashimoto, T. Shibauchi, Y. Matsuda, S. Yonezawa, Y. Muraoka, J. Yamaura, Y. Nagao, Z. Hiroi

    PHYSICA B-CONDENSED MATTER   403 ( 5-9 )   1068 - 1070   2008.4

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    To elucidate the superconducting gap structure and the influence of rattling motion on quasiparticle dynamics in the superconducting state of KOs2O6, the thermal conductivity and microwave surface impedance were measured at low temperatures. The magnetic field dependence of thermal conductivity and temperature dependence of penetration depth demonstrate full-gap superconductivity in KOs2O6. The quasiparticle scattering time is strongly enhanced in the superconducting state, indicating a strong electron inelastic scattering in the normal state. These results highlight that KOs2O6 is unique among superconductors with strong electron correlations. (c) 2007 Elsevier B.V. All rights reserved.

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  • Study of electronic structures for Fe thin films deposited on Si- and C-faces of 4H-SiC substrates by soft X-ray emission spectroscopy Reviewed

    M. Hirai, T. Wakita, H. Okazaki, D. Koishihara, Y. Muraoka, T. Yokoya

    APPLIED SURFACE SCIENCE   254 ( 1 )   26 - 28   2007.10

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    Silicon carbide (SiC) is a candidate material for electronic devices to operate upon crucial environment. Electronic states of silicides and/or carbide/graphite formed in metal/SiC contact system are fundamentally important from the viewpoint of device performance.
    We study interface electronic structure of iron thin film deposited on silicon (Si)- and carbon (C)-face of 4H-SiC(0 0 0 1) by using a soft X-ray emission spectroscopy (SXES). For specimens of Fe (50 nm)/4H-SiC (substrate) contact systems annealed at 700 and 900 degrees C, the Si L-2,L-3 emission spectra indicate different shapes and peak energies from the substrate depending on thermal-treated temperature. The product of materials such as silicides is suggested. Further, from comparison of Si L-2,L-3 emission spectra between Si- and C-face for the same annealing temperature at 700 degrees C, it is concluded that the similar silicides and/or ternary materials are formed on the two surfaces. However for those of 900 degrees C, the film on substrate is composed of the different silicide and/or ternary materials. (C) 2007 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.apsusc.2007.07.025

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  • Photoemission study of TiO2/VO2 interfaces Reviewed

    K. Maekawa, M. Takizawa, H. Wadati, T. Yoshida, A. Fujimori, H. Kumigashira, M. Oshima, Y. Muraoka, Y. Nagao, Z. Hiroi

    PHYSICAL REVIEW B   76 ( 11 )   115121   2007.9

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    We have measured photoemission spectra of two kinds of TiO2-capped VO2 thin films, namely, that with a rutile-type TiO2 capping layer (r-TiO2/VO2) and that with an amorphous TiO2 capping layer (a-TiO2/VO2). Below the metal-insulator transition temperature of the VO2 thin films, similar to 300 K, TiO2 and VO2 form an interface between a band insulator with the d(0) electronic configuration and a Mott (or Mott-Peierls) insulator with the d(1) electronic configuration. Metallic states were, however, not observed at the interfaces, in contrast to the interfaces between the d(0) band insulator SrTiO3 and the d(1) Mott insulator LaTiO3. We discuss possible origins of the difference between TiO2/VO2 and SrTiO3/LaTiO3, and suggest the importance of the polarity discontinuity in the latter interface. The stronger incoherent part was observed in r-TiO2/VO2 than in a-TiO2/VO2, suggesting Ti-V atomic diffusion due to the higher deposition temperature for r-TiO2/VO2.

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  • Interplay of superconductivity and rattling phenomena in beta-pyrochlore KOs2O6 studied by photoemission spectroscopy Reviewed

    T. Shimojima, Y. Shibata, K. Ishizaka, T. Kiss, A. Chainani, T. Yokoya, T. Togashi, X.-Y. Wang, C. T. Chen, S. Watanabe, J. Yamaura, S. Yonezawa, Y. Muraoka, Z. Hiroi, T. Saitoh, S. Shin

    PHYSICAL REVIEW LETTERS   99 ( 11 )   117003   2007.9

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    The electronic structure near the Fermi level (E-F) of the beta-pyrochlore superconductor KOs2O6 is studied using laser-excited ultrahigh-resolution photoemission spectroscopy. The superconducting gap clearly opens across the superconducting transition (T-c=9.6 K), with the strong electron-phonon coupling value of 2 Delta(0)/k(B)T(c)>= 4.56. A fitting analysis identifies clear anomalies at T-p=7.5 K in the temperature dependencies of the superconducting gap size and the quasiparticle relaxation lifetime. These anomalies and the fine spectral structures arising from phonons suggest that the existence of the rattling behavior of K ions significantly affects the superconductivity in KOs2O6.

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  • Precise control of band filling in NaxCoO2 Reviewed

    Daisuke Yoshizumi, Yuji Muraoka, Yoshihiko Okamoto, Yoko Kiuchi, Jun-Ichi Yamaura, Masahito Mochizuki, Masao Ogata, Zenji Hiroi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   76 ( 6 )   063705   2007.6

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    Electronic properties of the sodium cobaltate NaxCoO2 are systematically studied through a precise control of band filling. Resistivity, magnetic susceptibility and specific heat measurements are carried out on a series of high-quality polycrystalline samples prepared at 200 degrees C with Na content in a wide range of 0.35 <= x <= 0.70. It is found that dramatic changes in electronic properties take place at a critical Na concentration x* that lies between 0.58 and 0.59, which separates a Pauli paramagnetic and a Curie-Weiss metals. It is suggested that at x* the Fermi level touches the bottom of the a(1g) band at the Gamma point, leading to a crucial change in the density of states across x* and the emergence of a small electron pocket around the Gamma point for x > x*.

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  • Anomalous magnetic phase in an undistorted pyrochlore oxide Cd2Os2O7 induced by geometrical frustration Reviewed

    Akihiro Koda, Ryosuke Kadono, Kazuki Ohishi, Shanta R. Saha, Wataru Higemoto, Shigeki Yonezawa, Yuji Muraoka, Zenji Hiroi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   76 ( 6 )   063703   2007.6

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    We report on the muon spin rotation/relaxation study of a pyrochlore oxide, Cd2Os2O7, which exhibits a metal-insulator (MI) transition at T-MI similar or equal to 225 K without structural phase transition. It reveals strong spin fluctuation (>= 10(8) s(-1)) below the MI transition, suggesting a predominant role of geometrical spin frustration amongst Os5+ ions. Meanwhile, upon further cooling, an incommensurate spin density wave discontinuously develops below T-SDW similar or equal to 150 K. These observations strongly suggest the occurrence of an anomalous magnetic transition and associated change in the local spin dynamics in undistorted pyrochlore antiferromagnet.

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  • NMR observation of rattling phonons in the pyrochlore superconductor KOs2O6 Reviewed

    M. Yoshida, K. Arai, R. Kaido, M. Takigawa, S. Yonezawa, Y. Muraoka, Z. Hiroi

    PHYSICAL REVIEW LETTERS   98 ( 19 )   197002   2007.5

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    We report nuclear magnetic resonance studies on the beta-pyrochlore oxide superconductor KOs2O6. The nuclear relaxation at the K sites is entirely caused by fluctuations of the electric field gradient, which we ascribe to highly anharmonic low frequency oscillation (rattling) of K ions. A phenomenological analysis shows a crossover from overdamped to underdamped behavior of the rattling phonons with decreasing temperature and its sudden sharpening below the superconducting transition temperature T-c. Suppression of the Hebel-Slichter peak in the relaxation rate at the O sites below T-c also indicates strong electron-phonon coupling.

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  • Electronic structure of 3d(1) configuration vanadium oxides studied by soft X-ray and hard X-ray photoemission spectroscopy Reviewed

    R. Eguchi, M. Taguchi, M. Matsunami, K. Horiba, K. Yamamoto, A. Chainani, Y. Takata, M. Yabashi, D. Miwa, Y. Nishino, K. Tamasaku, T. Ishikawa, Y. Senba, H. Ohashi, I. H. Inoue, Y. Muraoka, Z. Hiroi, S. Shin

    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA   156   421 - 425   2007.5

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    We investigate the electronic structure of 3d(1) configuration vanadium oxides (VO2, SrVO3 and CaVO3) using soft X-ray (SX) and hard X-ray (HX) photoemission spectroscopy (PES). The valence band spectra of VO2 in SX- and HX-PES clearly show the opening of a gap at E-F across the metal-insulator transition. Spectral changes in the V 2p and O 1s core levels were also observed. In addition, 3d(1) configuration correlated metals SrVO3 and CaVO3 are typical materials whose valence band spectra are compared with dynamical mean-field theory. The V 2p and V 1s core level HX-PES of SrVO3 and CaVO3 show clear additional well-screened features. These features originate from bulk screening by a coherent band at EF. These spectra are nicely reproduced by a cluster model calculation, indicating a difference of the parameter V* for the interaction strength between the central V 3d orbitals and the coherent band. (c) 2007 Elsevier B.V. All rights reserved.

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  • Impurity effects on the Ni3+ triangular lattice of Ag2NiO2 Reviewed

    H. Yoshida, Y. Muraoka, Z. Hiroi

    JOURNAL OF PHYSICS-CONDENSED MATTER   19 ( 14 )   145234   2007.4

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    Silver oxonickelate Ag2NiO2 is a metallic compound presenting a spin- 1/2 triangular lattice. It exhibits a structural transition at T-s = 260 K, which may be related to e(g) orbital ordering, and an antiferromagnetic transition at T-N = 55 K. Impurity effects on its magnetic and electronic properties are examined by substituting Fe for Ni in Ag2Ni1-xFexO2 ( 0 <= x <= 0.3). A Curielike enhancement in magnetic susceptibility is observed at low temperature, which implies that most Fe3+ spins behave as free spins. Moreover, a large enhancement of residual resistivity and its suppression under magnetic fields are observed. Magnetic interactions in the Ni3+ triangular lattice are discussed.

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  • NMR study of beta-pyrochlore oxide superconductor KOs2O6 Reviewed

    M. Yoshida, K. Arai, R. Kaido, M. Takigawa, S. Yonezawa, Y. Muraoka, Z. Hiroi

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   310 ( 2 )   698 - 699   2007.3

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    We report results of NMR measurements on the K-39,K-41 and O-17 nuclei in KOs2O6. We found that the relaxation rate divided by temperature 1/(T1T) at the K sites is strongly enhanced compared with the values expected from the Knight shift and the Korringa relation. By comparing the results at the K-39 and K-41 sites, we conclude that the relaxation at the K sites is caused entirely by phonons via the electric quadrupole interaction. Consequently, our results provide information about the dynamics of isolated anharmonic vibration associated with the rattling of K ions. (c) 2006 Elsevier B. V. All rights reserved.

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  • Electronic structure of VO2/TiO2 : Nb upon photocarrier injection Reviewed

    R. Eguchi, S. Tsuda, T. Kiss, A. Chainani, Y. Muraoka, Z. Hiroi, S. Shin

    PHYSICAL REVIEW B   75 ( 7 )   073102   2007.2

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    We study the photocarrier injected electronic structure of VO2/TiO2:Nb (equivalent to p-n junction) thin-film heterostructure using photoemission spectroscopy, across the temperature-dependent metal-insulator transition in VO2. The valence band of VO2 shifts systematically to higher binding energy upon photocarrier injection (PCI). In the insulating phase, the energy shift as a function of irradiated power matches the surface photovoltage (SPV) behavior, while in the metallic phase, the energy shift follows the SPV trend but is reduced due to recombination. The temperature dependence of the energy shift between 200 and 330 K varies nearly linearly with the SPV. The study provides evidence for hole doping from TiO2:Nb to VO2 by the PCI effect.

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  • Thermal conductivity of the pyrochlore superconductor KOs2O6: Strong electron correlations and fully gapped superconductivity Reviewed

    Y. Kasahara, Y. Shimono, T. Shibauchi, Y. Matsuda, S. Yonezawa, Y. Muraoka, Z. Hiroi

    PHYSICAL REVIEW LETTERS   96 ( 24 )   247004   2006.6

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    To elucidate the nature of the superconducting ground state of the geometrically frustrated pyrochlore KOs2O6 (T-c=9.6 K), the thermal conductivity was measured down to low temperatures (similar to T-c/100). We found that the quasiparticle mean free path is strikingly enhanced below a transition at T-p=7.8 K, indicating enormous electron inelastic scattering in the normal state. In magnetic fields, the conduction at T -> 0 K is nearly constant up to similar to 0.4H(c2), in contrast with the rapid growth expected for superconductors with an anisotropic gap. This unambiguously indicates a fully gapped superconductivity, in contrast with previous studies. These results highlight that KOs2O6 is unique among superconductors with strong electron correlations.

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  • NMR studies of beta-pyrochlore superconductors with osmium, under hydrostatic pressure Reviewed

    K Arai, M Takigawa, S Yonezawa, Y Muraoka, Z Hiroi

    PHYSICA B-CONDENSED MATTER   378-80   878 - 879   2006.5

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    We report pressure effects on the Rb-87 nuclear relaxation rate 1/T-1 in the osmate superconductor RbOs2O6. The superconducting transition temperature T-c increases from 6.3 K at ambient pressure to 8.2 K at 2 GPa. Although 1/(T-1 T) is slightly enhanced by pressure at low temperatures, the temperature dependence of 1/(T-1 T) hardly changes below T-c. Even though T-c of RbOs2O6 at 2 GPa reaches a value close to that of KOs2O6 at ambient pressure (9.6 K), they show completely different nuclear relaxation behaviors. (c) 2006 Elsevier B.V. All rights reserved.

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  • High-pressure effects on the superconductivity of beta-pyrochlore oxides AOs(2)O(6) Reviewed

    Takaki Muramatsu, Nao Takeshita, Chikeko Terakura, Hidenori Takagi, Yoshinori Tokura, Shigeki Yonezawa, Yuji Muraoka, Zenji Hiroi

    PHYSICA B-CONDENSED MATTER   378-80   882 - 883   2006.5

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    High-pressure effects on the superconducting transitions of beta-pyrochlore oxide superconductors AOs(2)O(6) (A = Cs, Rb, K) are studied by measuring resistivity under high pressures up to 16 GPa. The superconducting transition temperature T-c first increases with increasing pressure in all the compounds and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa) and 10 K (0.6 GPa) for A = Cs, Rb and K, respectively. Finally, the superconductivity is suppressed completely at a critical pressure near 7 and 6 GPa for A = Rb and K and probably above 10 GPa for A = Cs. Characteristic changes in the temperature dependence of resistivity of RbOs2O6 under high pressure. The residual resistivity largely increases with pressure above 4 GPa and, as a result, resistivity indicates small temperature dependence down to 4.2 K at 7 GPa and application of further pressure up to 10 GPa indicates that temperature dependence of resistivity decrease below 100 K. This characteristic behavior in the beta-pyrochlore oxides may originate from the nesting of nearly octahedron shape of Fermi surface. (c) 2006 Elsevier B.V. All rights reserved.

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  • Upper critical field of beta-pyrochlore KOs2O6 single crystals Reviewed

    E Ohmichi, T Osada, S Yonezawa, Y Muraoka, Z Hiroi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   75 ( 4 )   045002   2006.4

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  • Role of electron-electron and electron-phonon interaction effects in the optical conductivity of VO2 Reviewed

    K Okazaki, S Sugai, Y Muraoka, Z Hiroi

    PHYSICAL REVIEW B   73 ( 16 )   165116   2006.4

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    We have investigated the charge dynamics of VO2 by optical reflectivity measurements. Optical conductivity clearly shows a metal-insulator transition. In the metallic phase, a broad Drude-like structure is observed. On the other hand, in the insulating phase, a broad peak structure around 1.3 eV is observed. It is found that this broad structure observed in the insulating phase shows a temperature dependence. We attribute this to the electron-phonon interaction as in the photoemission spectra.

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  • Spin-1/2 triangular lattice with orbital degeneracy in a metallic oxide Ag2NiO2 Reviewed

    H Yoshida, Y Muraoka, T Sorgel, M Jansen, Z Hiroi

    PHYSICAL REVIEW B   73 ( 2 )   020408(R)   2006.1

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    A metallic and magnetic transition metal oxide Ag2NiO2 is studied by means of resistivity, magnetic susceptibility, specific heat, and x-ray diffraction. The crystal structure is characterized by an alternating stacking of a Ni3+O2 layer and a (Ag-2)(+) layer, the former realizing a spin-1/2 triangular lattice with e(g) orbital degeneracy and the latter providing itinerant electrons. It is found that the NiO2 layer exhibits orbital ordering at T-s = 260 K and antiferromagnetic spin ordering at T-N= 56 K. Moreover, a moderately large mass enhancement is found for the itinerant electrons, suggesting a significant contribution from the nearly localized Ni 3d state to the Ag 5s state that forms a broad band.

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  • Crystal structure of the pyrochlore oxide superconductor KOs2O6 Reviewed

    JI Yamaura, S Yonezawa, Y Muraoka, Z Hiroi

    JOURNAL OF SOLID STATE CHEMISTRY   179 ( 1 )   336 - 340   2006.1

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    We report the single-crystal X-ray analysis of the structure of the pyrochlore oxide superconductor KOs2O6. The structure was identified as the beta-pyrochlore structure with space group Fd (3) over barm and lattice constant a = 10.089(2) angstrom at 300 K: the K atom is located at the 8b site, not at the 16d site as in conventional pyrochlore oxides. We found an anomalously large atomic displacement parameter U-iso = 0.0735(8) angstrom(2) at 300 K for the K cation, which suggests that the K cation weakly bound to an oversized OS12O18 cage exhibits intensive rattling, as recently observed for clathrate compounds. The rattling of A cations is a common feature in the series of flpyrochlore oxide superconductors AOs(2)O(6) (A = Cs, Rb and K), and is greatest for the smallest K cation. (c) 2005 Elsevier Inc. All rights reserved.

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  • Metal-insulator transition in VO2 studied by optical spectroscopy

    Kozo Okazaki, Shunji Sugai, Yuji Muraoka, Zenji Hiroi

    LOW TEMPERATURE PHYSICS, PTS A AND B   850   1229 - +   2006

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    We have investigated the charge dynamics of VO2 by optical reflectivity measurements. Optical conductivity clearly shows a metal-insulator transition. In the metallic phase, a broad Drude-like structure is observed. On the other hand, in the insulating phase, a broad peak structure around 1.3 eV is observed. It is found that this broad structure observed in the insulating phase shows strong temperature dependence. We attribute this to the electron-phonon interaction as in the photoemission spectra.

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  • Spin-1/2 triangular laiftice in Ag2NiO2 Reviewed

    Hiroyuki Yoshida, Yuji Muraoka, Zenji Hiroi, Timo Soergel, Martin Jansen

    LOW TEMPERATURE PHYSICS, PTS A AND B   850   1089 - +   2006

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    A novel metallic compound with a spin-1/2 triangular lattice is reported. It is a silveroxonickelate Ag2NiO2 containing a NiO2 layer which possesses a spin-1/2 triangular lattice with twofold spin and twofold orbital degeneracy. It is found that a structural transition takes place at T-s = 260 K, which may be related to orbital ordering, and long-range antiferromagnetic order sets in below T-N = 54 K.

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  • Erratum to Three Papers on the

    Hiroi Zenji, Yonezawa Shigeki, Yamaura Jun-Ichi, Muramatsu Takaki, Matsushita Yoshitaka, Muraoka Yuji

    J Phys Soc Jpn   74 ( 12 )   3400 - 3400   2005.12

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    DOI: 10.1143/JPSJ.74.3400

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  • Retraction: "Unprecedented Superconductivity in

    Hiroi Zenji, Yonezawa Shigeki, Muraoka Yuji

    J Phys Soc Jpn   74 ( 12 )   3399 - 3399   2005.12

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  • Photocarrier-injected electronic structure of VO2/TiO2 : Nb Reviewed

    R Eguchi, S Shin, A Fukushima, T Kiss, T Shimojima, Y Muraoka, Z Hiroi

    APPLIED PHYSICS LETTERS   87 ( 20 )   201912   2005.11

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    We study the effect of photocarrier injection on the electronic structure of VO2/TiO2:Nb thin films using photoemission spectroscopy. The results indicate that the valence band and core electronic states of VO2 shift systematically to lower binding energy upon photocarrier injection, consistent with doping in a rigid-band picture. The shift in binding energy, and its saturation, follows the known photovoltage behavior. In addition, the V 3d states near E-F exhibit a redistribution/transfer of spectral weight, similar to the temperature dependent insulator to metal transition in VO2. The study provides evidence for hole-doping induced electronic structure changes due to the photocarriers in VO2. (C) 2005 American Institute of Physics.

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  • Photocarrier injection and current-voltage characteristics of La0.8Sr0.2MnO3/SrTiO3 : Nb heterojunction at low temperature Reviewed

    T Muramatsu, Y Muraoka, Z Hiroi

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS   44 ( 10 )   7367 - 7371   2005.10

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    An epitaxial heterojunction made of a p-type perovskite manganite La0.8Sr0.2MnO3 film and an n-type strontium titanate SrTiO3:Nb substrate has been fabricated by the pulsed laser deposition technique. The current-voltage (I-V) characteristics and photovoltaic properties are measured under UV light irradiation in a wide temperature range down to 10 K. It is found that the junction acts as an efficient UV photodiode with a large external quantum efficiency of 28%. It is also demonstrated that the manganite film can be doped with a certain amount of holes by photocarrier injection. The maximum surface hole density is estimated to be 3.0 x 10(13) cm(-2).

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  • Anomalous pressure dependence of the superconducting transition temperature of beta-pyrochlore AOs(2)O(6) oxides Reviewed

    T Muramatsu, N Takeshita, C Terakura, H Takagi, Y Tokura, S Yonezawa, Y Muraoka, Z Hiroi

    PHYSICAL REVIEW LETTERS   95 ( 16 )   167004   2005.10

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    High-pressure effects on the superconducting transitions of beta-pyrochlore oxide superconductors AOs(2)O(6) (A=Cs,Rb,K) are studied by measuring resistivity under high pressures up to 10 GPa. The superconducting transition temperature T-c first increases with increasing pressure in every compound and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa), and 10 K (0.6 GPa) for A=Cs, Rb, and K, respectively. Finally, the superconductivity is suppressed completely at a critical pressure near 7 GPa and 6 GPa for A=Rb and K and probably above 10 GPa for A=Cs. Characteristic changes in the coefficient A of the T-2 term in resistivity and residual resistivity are observed, both of which are synchronized with the corresponding change in T-c.

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  • Photocarrier injection to organic compounds Reviewed

    Jun-Ichi Yamaura, Yuji Muraoka, Takaki Muramatsu, Touru Yamauchi, Zenji Hiroi

    Synthetic Metals   152 ( 1-3 )   385 - 388   2005.9

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    DOI: 10.1016/j.synthmet.2005.07.115

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  • Photogenerated carrier injection to an n-type copper oxide superconductor Reviewed

    Y Muraoka, T Muramatsu, Z Hiroi

    THIN SOLID FILMS   486 ( 1-2 )   82 - 85   2005.8

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    We have fabricated an isotype heterostructure made of an n-type superconductor (Sr0.89Nd0.11)CuO2 film and an n-type SrTiO3:Nb substrate by using the pulsed laser deposition technique and measured the current-voltage and photovoltaic properties under ultraviolet (UV) light irradiation. A large photovoltage of 0.8 V, which is positive to the film, is observed. This means that the photogenerated hole carriers in the SrTiO3:Nb substrate are injected to the film. Under UV light irradiation, the superconducting transition of the film slightly shifts to lower temperature. The effect of the photocarrier injection on the superconducting transition temperature is discussed in terms of a proposed energy level diagram of the (Sr0.89Nd0.11)CuO2/SrTiO3:Nb heterostructure. (c) 2005 Elsevier B.V. All rights reserved.

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  • Second anomaly in the specific heat of beta-pyrochlore oxide superconductor KOs2O6 Reviewed

    Z Hiroi, S Yonezawa, JI Yamaura, T Muramatsu, Y Muraoka

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 6 )   1682 - 1685   2005.6

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    Resistivity and specific heat have been measured on a single-crystalline sample of a beta-pyrochlore oxide superconductor, KOs2O6. It is found that a second peak in specific heat, which may evidence an unknown phase transition, appears at around T-p similar to 7.5 K below the superconducting transition temperature T-c = 9.53 K. Applying magnetic fields up to 14 T, T-c is reduced gradually down to 7.1 K, while T-c is slightly raised and becomes even higher than T-c at 14T, which implies that the second anomaly is not associated directly with the superconductivity. It is demonstrated, however, that there is significant communication between the two anomalies, suggesting that they come from the same electrons. It is also reported that the Sommerfeld coefficient gamma in KOs2O6 is possibly much larger than those in other members of beta-pyrochlore oxide superconductors, RbOs2O6 (T-c = 6.3 K) and CsOs2O6 (T-c = 3.3 K).

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  • Photoemission study of YBa2Cu3Oy thin films under light illumination Reviewed

    D Asakura, JW Quilty, K Takubo, S Hirata, T Mizokawa, Y Muraoka, Z Hiroi

    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA   144   499 - 502   2005.6

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    The photocarrier injection (PCI) effect is observed at the heterojunction of YBa2Cu3Oy (YBCO) thin film and Nb-doped SrTiO3 (STO:Nb) substrate. PCI is expected as a new carrier doping method in strongly correlated systems instead of chemical substitution. We have studied the nature of PCI in YBCO/STO:Nb using X-ray photoemission spectroscopy with pulsed laser excitation. In the core-level spectra, the energy shift to higher binding energy by 0.5 eV is observed under the laser illumination with frequency of 30 Hz. The energy shift corresponds to the photovoltage, which arises in the interface. In addition, we have measured the spectra varying frequency of the laser. The energy shift obviously depends on the frequency, which is related to the lifetime of the injected photoholes. (c) 2005 Elsevier B.V. All rights reserved.

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  • Possible anisotropic order parameter in pyrochlore superconductor KOs2O6 probed by muon spin rotation Reviewed

    A Koda, W Higemoto, K Ohishi, Saha, SR, R Kadono, S Yonezawa, Y Muraoka, Z Hiroi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 6 )   1678 - 1681   2005.6

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    Magnetic penetration depth (lambda(eff)) in a pyrochlore superconductor KOs2O6 was studied by means of muon spin rotation (mu SR). The temperature dependence of the transverse spin relaxation rate, which is proportional to lambda(-2)(eff), exhibits a considerable deviation from that expected for the empirical two-fluid model (proportional to T-4), obeying a T-2 tendency. Furthermore, lambda(eff) apparently increases with increasing applied field, suggesting the presence of nonlinear and nonlocal effects. The present result strongly suggests that the superconducting order parameter in KOsO6 is anisotropic or multigapped with a small energy gap.

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  • NMR studies of the new superconductors AOs(2)O(6) (A = K, Rb) Reviewed

    K Arai, J Kikuchi, K Kodama, M Takigawa, S Yonezawa, Y Muraoka, Z Hiroi

    PHYSICA B-CONDENSED MATTER   359   488 - 490   2005.4

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    We report results of nuclear magnetic resonance (NMR) experiments on K-39 and Rb-87 nuclei in the new superconductors AOs(2)O(6) (A = K or Rb). These compounds crystallize in the beta-pyrochlore structure. In the superconducting phase, we found a small peak in 1/(T1T) for 87 Rb slightly below the superconducting transition temperature (T-c) but no peak for K-39. In the normal state of KOs2O6, we observed a clear pseudogap behavior similar to what has been observed in high T-c cuprates. (c) 2005 Elsevier B.V. All rights reserved.

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  • Specific heat of the beta-pyrochlore oxide superconductors CsOs2O6 and RbOs2O6 Reviewed

    Z Hiroi, S Yonezawa, T Muramatsu, J Yamaura, Y Muraoka

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 4 )   1255 - 1262   2005.4

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    Two beta-pyrochlore oxide superconductors, CsOs2O6 and RbOs2O6, are studied thermodynamically by measuring specific heat on polycrystalline samples. It is found that a Sommerfeld coefficient gamma is nearly equal, 20mJ/K-2 mol Os, in the two oxides with different superconducting transition temperatures; T-c = 3.3 and 6.3 K, respectively. This suggests that the density of states at the Fermi level is not a crucial parameter to determine the T-c of the beta-pyrochlore oxide superconductors, which is incompatible with the general expectation for a conventional BCS-type superconductor. Anomalous lattice contributions to specific heat at low temperature are also reported, which may come from nearly localized phonon modes associated with the rattling of the alkali metal ions weakly bound in an oversized cage formed by OsO6 octahedra.

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  • Photoemission study of YBa2Cu3Oy thin films under light illumination Reviewed

    D Asakura, JW Quilty, K Takubo, S Hirata, T Mizokawa, Y Muraoka, Z Hiroi

    PHYSICAL REVIEW LETTERS   93 ( 24 )   2004.12

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    Heterojunctions of Nb-doped SrTiO3 substrate and YBa2Cu3Oy thin films show photoconductivity and photovoltaic effects due to photocarrier injection. Photocarrier injection is expected to be a new carrier doping method in strongly correlated systems instead of chemical substitution. We have studied the nature of photocarrier injection in YBa2Cu3Oy/SrTiO3:Nb using x-ray photoemission spectroscopy with pulsed laser excitation. The core-level spectra shift to higher binding energy by 0.78 eV under pulsed laser illumination at 30 Hz. The energy shift corresponds to the photovoltage, which arises at the interface. In addition, we have observed that the energy shift strongly depends on the frequency of the laser. The lifetime of the injected photoholes has been estimated to be 40 ms by analyzing the frequency dependence.

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  • Photocarrier injection and the I-V characteristics of La0.8Sr0.2MnO3/SrTiO3 : Nb heterojunctions Reviewed

    T Muramatsu, Y Muraoka, Z Hiroi

    SOLID STATE COMMUNICATIONS   132 ( 5 )   351 - 354   2004.11

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    Oxide heterojunctions made of p-type La0.8Sr0.2MnO3 (LSMO) and niobium-doped n-type SrTiO3 (STO:Nb) have been fabricated by the pulsed laser deposition (PLD) technique and characterized under UV light irradiation by measuring the current-voltage, photovoltaic properties and the junction capacitance. It is shown that the heterojunctions work as an efficient UV photodiode, in which photogenerated holes in the STO:Nb substrate are injected to the LSMO film. The maximum surface hole density Q/e and external quantum efficiency gamma are estimated to be 8.3 X 10(12) cm(-2) and 11% at room temperature, respectively. They are improved significantly in a p-i-n junction of LSMO/STO/STO:Nb, where Q/e and gamma are 3.0 X 10(13) cm(-2) and 27%, respectively. (C) 2004 Elsevier Ltd. All rights reserved.

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  • Photogenerated hole carrier injection to YBa2Cu 3O7-x in an oxide heterostructure Reviewed

    Y. Muraoka, T. Muramatsu, J. Yamaura, Z. Hiroi

    Applied Physics Letters   85 ( 14 )   2950 - 2952   2004.10

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    Hole doping in the YBa2Cu3O7-X in an oxide heterostructure was analyzed. The current-voltage and photovoltaic properties of YBa2Cu3O7-X were also observed under ultraviolet light irradiation at room temperature. The maximum surface hole carrier density injected was found to be 3.5*1013 cm-2 at L=44 mW/cm2. The results show that the photocarrier injection technique could be used in transition metal oxides to control the hole carrier density.

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  • High pressure effects on superconductivity in the beta-pyrochlore oxides AOs(2)O(6) (A = K, Rb, Cs) Reviewed

    T Muramatsu, S Yonezawa, Y Muraoka, Z Hiroi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 10 )   2912 - 2913   2004.10

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  • New beta-pyrochlore oxide superconductor CsOs2O6 Reviewed

    S Yonezawa, Y Muraoka, Z Hiroi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 7 )   1655 - 1656   2004.7

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    The discovery of the new beta-pyrochlore oxide superconductor CsOs2O6 with T-c = 3.3 K is reported. It is the third superconductor in the family of beta-pyrochlore oxides, following KOs2O6 with T-c = 9.6 K and RbOs2O6 with T-c = 6.3 K. The T-c of this series decreases with increasing ionic radius of alkaline metal ions, imposing a negative chemical pressure upon the Os pyrochlore lattice.

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  • Unprecedented superconductivity in beta-pyrochlore osmate KOs2O6 Reviewed

    Z Hiroi, S Yonezawa, Y Muraoka

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 7 )   1651 - 1654   2004.7

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    Superconductivity in the potassium osmium oxide KOs2O6 crystallizing in the beta-pyrochlore structure is studied by electrical resistivity, magnetic susceptibility and specific heat measurements. It is the second superconductor in the family of pyrochlore oxides, following the alpha-type pyrochlore oxide Cd2Re2O7 which is believed to be a conventional s-wave superconductor. The superconducting transition temperature T-c of KOs2O6 is 9.6 K, almost one order higher than the T-c = 1.0 K of Cd2Re2O7. Moreover, the superconductivity of KOs2O6 is markedly robust under high magnetic fields, with a large upper critical magnetic field H-c2 of about 38 T, which seems to exceed Pauli's limit expected for conventional superconductivity. This is also in contrast to the case of Cd2Re2O7, in which the H-c2 is 0.29 T, much smaller than the corresponding Pauli's limit. These distinct contrasts strongly suggest that the mechanism of superconductivity is essentially different between the two pyrochlore oxides.

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  • Photocarrier injection to perovskite manganites Reviewed

    T. Muramatsu, Y. Muraoka, T. Yamauchi, J. Yamaura, Z. Hiroi

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   272   E787 - E788   2004.5

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    We have fabricated (La, Sr)MnO3 thin films on n-type SrTiO3 substrates doped with Nb by means of the pulsed laser deposition technique. It is shown that hole carriers photogenerated in the substrates under UV light irradiation are injected efficiently to the. lms. By measuring the out-of-plane voltage of the heterojunction the surface density of hole carriers injected to (La, Sr)MnO3 is estimated: It is at most 1.6 x 10(13) cm(-2), but is improved up to 3.1 x 10(13) cm(-2) by modifying the junction structure, i.e., inserting a pure SrTiO3 layer between the film and the substrate. (C) 2004 Elsevier B.V. All rights reserved.

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  • Efficient photocarrier injection to transition metal oxides Reviewed

    Y Muraoka, T Yamauchi, T Muramatsu, J Yamaura, Z Hiroi

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   272   448 - 449   2004.5

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    We have fabricated transition metal oxide (TMO) films on n-type titanium oxide substrates, and measured in-plane resistance under ultraviolet light irradiation. A dramatic decrease in the resistance and enhancement of the superconducting critical temperature are observed for VO2/TiO2:Nb and YBa2Cu3O2/SrTiO3:Nb, respectively. Out-of-plane voltage measurements under light irradiation indicate hole-carrier injection from the substrate to the film in both the cases. The present photocarrier injection technique could apply to many TMOs to control the hole carrier density externally. (C) 2004 Elsevier B.V. All rights reserved.

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  • New pyrochlore oxide superconductor RbOs2O6 Reviewed

    S Yonezawa, Y Muraoka, Y Matsushita, Z Hiroi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 4 )   819 - 821   2004.4

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    We report the discovery of a new pyrochlore oxide superconductor RbOs2O6. The compound crystallizes in the same beta-pyrochlore structure as the recently discovered superconductor KOs2O6, where Os atoms form a corner-sharing tetrahedral network called the pyrochlore lattice with Rb or K atoms in the cage. Resistivity, magnetic susceptibility and specific heat measurements on polycrystalline samples evidence a bulk superconductivity with T-c = 6.3 K.

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  • Photoemission study of the metal-insulator transition in VO 2/TiO2(001): Evidence for strong electron-electron and electron-phonon interaction Reviewed

    K. Okazaki, H. Wadati, A. Fujimori, M. Onoda, Y. Muraoka, Z. Hiroi

    Physical Review B - Condensed Matter and Materials Physics   69 ( 16 )   1 - 165104   2004.4

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    We have made a detailed temperature-dependent photoemission study of VO2/TiO2(001) thin films, which show a metal-insulator transition at ∼300 K. Clean surfaces were obtained by annealing the films in an oxygen atmosphere. Spectral weight transfer between the coherent and incoherent parts accompanying the metal-insulator transition was clearly observed. We also observed a hysteretic behavior of the spectra for heating-cooling cycles. We have derived the "bulk" spectrum of the metallic phase and found that it has a strong incoherent part. The width of the coherent part is comparable to that given by band-structure calculation in spite of its reduced spectral weight, indicating that the momentum dependence of the self-energy is significant. This is attributed to by ferromagnetic fluctuation arising from Hund's rule coupling between different d orbitals as originally proposed by Zylbersztejn and Mott. In the insulating phase, the width of the V 3d band shows strong temperature dependence. We attribute this to electron-phonon interaction and have reproduced it using the independent boson model with a very large coupling constant.

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  • Epitaxial strain effects on the metal-insulator transition in V2O3 thin films Reviewed

    S Yonezawa, Y Muraoka, Y Ueda, Z Hiroi

    SOLID STATE COMMUNICATIONS   129 ( 4 )   245 - 248   2004.1

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    Effects of epitaxial stress on the metal-insulator transition of V2O3 have been studied for in the form of epitaxial thin films grown on alpha-Al2O3 (0001) and LiTaO3 (0001) substrates. A metallic phase is stabilized down to 2 K in the V2O3 thin film on alpha-Al2O3 (0001), where the a-axis is compressed by 4% owing to large epitaxial stress. On the other hand, the transition temperature T-MI is raised by 20 K from the value of 170 K in bulk samples in the film on LiTaO3 (0001), where the a-axis is expanded. These results suggest an intimate relationship between the a-axis length and T-MI, in V2O3. The conductivity of the metallic ultrathin films shows logarithmic temperature dependence below 20 K, probably due to the Anderson localization in two-dimensional systems. (C) 2003 Elsevier Ltd. All rights reserved.

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  • Superconductivity in a pyrochlore-related oxide KOs2O6 Reviewed

    S Yonezawa, Y Muraoka, Y Matsushita, Z Hiroi

    JOURNAL OF PHYSICS-CONDENSED MATTER   16 ( 3 )   L9 - L12   2004.1

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    We report the discovery of a new superconductor KOs2O6. The compound crystallizes in a defect pyrochlore structure, where Os atoms form a corner-sharing tetrahedral network called the pyrochlore lattice. Resistivity and magnetic susceptibility measurements on a polycrystalline sample provide evidence of bulk superconductivity with T-c = 9.6 K.

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  • Photocarrier injection to YBa2CU3O7-x thin films Reviewed

    Y Muraoka, T Muramatsu, T Yamauchi, J Yamaura, Z Hiroi

    FRONTIERS IN SUPERCONDUCTING MATERIALS-NEW MATERIALS AND APPLICATIONS   3   173 - 175   2004

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    We have prepared YBa2Cu3O7-x thin films on n-type SrTiO3 substrates doped with Nb, and measured the in-plane resistance under ultraviolet light irradiation. An enhancement of the superconducting critical temperature is observed from 25 K up to 30 K with increasing light irradiance. Out-of-plane voltage measurements under light irradiation indicate hole carrier injection from the substrate to the film.

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  • Efficiency of photocarrier injection in a VO2/TiO2 : Nb heterostructure Reviewed

    Z Hiroi, T Yamauchi, Y Muraoka, T Muramatsu, J Yamaura

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 12 )   3049 - 3052   2003.12

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    The efficiency of photocarrier injection in a VO2/TiO2:Nb heterostructure is studied by measuring I-V characteristics at room temperature under ultraviolet light irradiation. It is revealed that photogenerated hole carriers in the TiO2:Nb substrate are injected and accumulated in the VO2 film by the photovoltaic effect. The surface charge density is controlled successfully in a wide range of 10(9)-10(13) cm(-2) as a function of light irradiance. The maximum hole density of 9 x 10(18) cm(-3) is attained at a light irradiance of 133 mW/cm(2), which is estimated by assuming the uniform distribution of holes in the film. It is suggested that high efficiency can be achieved by utilizing the large dielectric constant of titanium oxide substrates.

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  • Ultraviolet light selective photodiode based on an organic-inorganic heterostructure Reviewed

    J Yamaura, Y Muraoka, T Yamauchi, T Muramatsu, Z Hiroi

    APPLIED PHYSICS LETTERS   83 ( 11 )   2097 - 2099   2003.9

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    We show a perfect ultraviolet (UV) light selective and sensitive photovoltaic cell easily fabricated. The device consists of a water-soluble p-type semiconducting polymer PEDOT-PSS: poly(3,4-ethylenedioxythiophene) doped by poly(4-styrenesulfonate) film deposited on a Nb-doped titanium oxide (SrTiO3:Nb) substrate. For the PEDOT-PSS/SrTiO3:Nb heterostructure, the photosensitivity at zero bias for the UV light with L=1 mW/cm(2) is estimated to be 0.05 A/W, corresponding to a quantum yield of 16% electron/photon. This device is only activated in the UV region (lambda<390 nm), and then, it exhibits a large response to the UV-B light (290-320 nm). (C) 2003 American Institute of Physics.

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  • Photocarrier injection to transition metal oxides Reviewed

    Y Muraoka, Z Hiroi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 4 )   781 - 784   2003.4

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    An efficient and clean method of doping transition metal oxides (TMOs) with hole carriers is presented. We have fabricated oxide heterostructures made of various TMO thin films grown on n-type titanium oxide substrates, and measured in-plane resistance under ultraviolet light irradiation. It is shown that the resistance of the insulating TMOs is reduced significantly with increasing light irradiance, as a result of photoinduced hole carrier injection from the titanium oxide substrates. A generic band structure for the heterojunctions is proposed, in which a large potential slope and a small barrier exist near the interface for photoinduced holes and electrons in the titanium oxides, respectively. This photocarrier injection (PCI) technique would provide us with a useful method to achieve the external control of hole carrier density in TMOs.

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  • Correlations and semimetallic behaviors in pyrochlore oxide Cd2Re2O7 Reviewed

    Z Hiroi, M Hanawa, Y Muraoka, H Harima

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 1 )   21 - 24   2003.1

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    Electronic properties of the metallic pyrochlore oxide Cd2Re2O7 are studied by means of electrical resistivity and Hall measurements. Semimetallic band structures are revealed as expected from band structure calculations. It is found that large changes in carrier density and mass occur at the structural phase transition at T-s1 = 200K. A large mass enhancement is observed, particularly for the high-temperature phase with the ideal pyrochlore structure, suggesting that an anomalous correlation has an important effect on the itinerant electrons in the pyrochlore lattice.

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  • Efficient photocarrier injection in a transition metal oxide heterostructure Reviewed

    Y Muraoka, T Yamauchi, Y Ueda, Z Hiroi

    JOURNAL OF PHYSICS-CONDENSED MATTER   14 ( 49 )   L757 - L763   2002.12

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    An efficient method for doping a transition metal oxide (TMO) with hole carriers is presented: photocarrier injection (PCI) in an oxide heterostructure. It is shown that an insulating vanadium dioxide (VO2) film is rendered metallic under light irradiation by PCI from an n-type titanium dioxide (TiO2) substrate doped with Nb. Consequently, a large photoconductivity, which is exceptional for TMOs, is found in the VO2/TiO2:Nb heterostructure. We propose an electronic band structure where photoinduced holes created in TiO2:Nb can be transferred into the filled V 3d band via the low-lying O 2p band of VO2.

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  • Second phase transition in pyrochlore oxide Cd2Re2O7 Reviewed

    Z Hiroi, JI Yamaura, Y Muraoka, M Hanawa

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   71 ( 7 )   1634 - 1636   2002.7

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    Evidence of another phase transition at 120 K in the metallic pyrochlore oxide CdRe2O7, following a structural transition at 200K and followed by a superconducting transition at 1.0K, is obtained by resistivity, magnetoresistance, specific heat, and X-ray diffraction measurements. The results indicate unique successive structural and electronic transitions in the pyrochlore compound, revealing an interesting interplay between the crystal and electronic structures on the itinerant electron system in the pyrochlore lattice.

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  • Large modification of the metal-insulator transition temperature in strained VO2 films grown on TiO2 substrates Reviewed

    Y Muraoka, Y Ueda, Z Hiroi

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   63 ( 6-8 )   965 - 967   2002.6

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    Epitaxial thin films of vanadium dioxide (VO2) have been grown on TiO2 (001) and (110) substrates and the effect of uniaxial stress along the c-axis on the metal-insulator transition (MIT) Of VO2 has been studied. A large reduction in the transition temperature T-M1 from 341 K for a single crystal to 300 K has been observed in the film on TiO2 (001) where the c-axis length is compressed owing to an epitaxial stress, while the T-M1 has been increased to 369 K in the film on TiO2 (110) where the c-axis length is expanded. The correlation between the c-axis length and T-M1 is suggested: the shorter c-axis length results in the lower T-M1. (C) 2002 Elsevier Science Ltd. All rights reserved.

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  • Structural phase transition in the superconducting pyrochlore oxide Cd2Re2O7 Reviewed

    M Hanawa, J Yamaura, Y Muraoka, F Sakai, Z Hiroi

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   63 ( 6-8 )   1027 - 1030   2002.6

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    We report a structural phase transition found at T-s = 200 K in a pyrochlore oxide Cd2Re2O7 which shows superconductivity at T-c = 1.0 K. X-ray diffraction experiments indicate that the phase transition is of the second-order, from a high-temperature phase with the ideal cubic pyrochlore structure (space group Fd (3) over barm) to a low-temperature phase with another cubic structure (space group F (4) over bar 3m). It is accompanied by a dramatic change in the resistivity and magnetic susceptibility and thus must induce a significant change in the electronic structure of Cd2Re2O7. (C) 2002 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0022-3697(02)00090-2

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  • Metal-insulator transition of VO2 thin films grown on TiO2 (001) and (110) substrates Reviewed

    Y Muraoka, Z Hiroi

    APPLIED PHYSICS LETTERS   80 ( 4 )   583 - 585   2002.1

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    The effect of uniaxial stress along the c axis on the metal-insulator transition of VO2 has been studied in the form of epitaxial thin films grown on TiO2 (001) and (110) substrates. A large reduction in the transition temperature T-MI from 341 K for a single crystal to 300 K has been observed in the film on TiO2 (001) where the c-axis length is compressed owing to an epitaxial stress, while the T-MI has been increased to 369 K in the film on TiO2 (110) where the c-axis length is expanded. The correlation between the c-axis length and T-MI is suggested: the shorter c-axis length results in the lower T-MI. (C) 2002 American Institute of Physics.

    DOI: 10.1063/1.1446215

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  • Superconductivity at 1 K in Cd2Re2O7 Reviewed

    M Hanawa, Y Muraoka, T Tayama, T Sakakibara, J Yamaura, Z Hiroi

    PHYSICAL REVIEW LETTERS   87 ( 18 )   187001   2001.10

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    We report the first pyrochlore oxide superconductor Cd2Re2O7. Resistivity, magnetic susceptibility, and specific heat measurements on single crystals evidence a bulk superconductivity at 1 K. Another phase transition found at 200 K suggests, that a peculiar electronic structure lies behind the superconductivity.

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  • Atomic ordering in the LaFe0.5Mn0.5O3 solid solution film Reviewed

    K Ueda, Y Muraoka, H Tabata, T Kawai

    APPLIED PHYSICS LETTERS   78 ( 4 )   512 - 514   2001.1

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    LaFe0.5Mn0.5O3 solid solution films have been formed on SrTiO3 (111) substrates using a pulsed laser deposition technique and their magnetic properties have been examined. The films showed ferromagnetic (or ferromagnetic) behavior with a Curie temperature of 380 K and the saturation magnetization was estimated to be about 1.5 mu (B) per magnetic ion site (B site). The x-ray photoemission spectra indicated that this behavior was due to the partial ordering of magnetic ions (Fe and Mn ions) which is caused by the charge disproportion between Fe and Mn ions under the film formation conditions. (C) 2001 American Institute of Physics.

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  • Effects of light-irradiation on spin-glass state and magnetoresistive properties of Zn0.5Co0.5Fe2O4 spinel ferrite films Reviewed

    Y Muraoka, H Tabata, T Kawai

    SOLID STATE COMMUNICATIONS   120 ( 5-6 )   255 - 258   2001

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    Spin-glass spinel ferrite Zn0.5Co0.5Fe2O4 films were prepared on alpha -Al2O3(0001) substrates and the effect of light-irradiation on the spin-glass state was studied. The magnetization of prepared films showed a broad maximum at 260 K in a zero-field-cooled (ZFC) process, which is characteristic of a spin glass or a cluster glass. When shining light on the film under H = 1 kOe, the magnetization in the ZFC process increased, and returned to its original level when the light was turned off. This switching behavior was confirmed to work even at 350 K. magnetoresistance (MR) and photo-induced MR effects of this film are also described. (C) 2001 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0038-1098(01)00373-8

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  • Room-temperature spin glass and its photocontrol in spinel ferrite films Reviewed

    Y Muraoka, H Tabata, T Kawai

    APPLIED PHYSICS LETTERS   77 ( 24 )   4016 - 4018   2000.12

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    Room-temperature spin-glass states have been found in (Mg,Fe){Mg,Fe,Ti}(2)O-4 spinel ferrite thin films formed on Al2O3(0001) and SrTiO3(111) substrates. This elevated-temperature spin-glass state has been achieved by the fine tuning of spin states through the control of composition, random oxygen deficiencies, and the stress induced by the film/substrate lattice mismatch in the ferrite films. We have demonstrated the change of magnetic state by means of light irradiation from spin glass to a ferrimagnet over a wide range of temperatures below 290 K. The direct photoexcitation of spins with photon energy of 2.0 eV, which corresponds to the spin excitation energy for Fe ions, is the most effective for realizing photoinduced magnetization. (C) 2000 American Institute of Physics. [S0003-6951(00)01750-2].

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  • Photoexcited spin-glass state in (Mg, Fe){Mg,Fe,Ti}O-4 spinel ferrite films Reviewed

    Y Muraoka, H Tabata, T Kawai

    JOURNAL OF APPLIED PHYSICS   88 ( 12 )   7223 - 7229   2000.12

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    Spin-glass states above room temperature have been found in (Mg, Fe){Mg,Fe,Ti}(2)O-4 spinel ferrite thin films formed on Al2O3 (0001) and SrTiO3 (111) substrates. The films show a long-time relaxation of the magnetization in zero-field-cooled operation and a frequency dependence of the cusp temperature in ac susceptibility measurement, both of which are typical characteristics of a spin glass. This high-temperature spin-glass state has been achieved by the fine tuning of spin states through the control of composition, random oxygen deficiencies, and the stress induced by the film/substrate lattice mismatch, all of which give rise to effects that enhance the exchange interaction of spins in the ferrite films. We have demonstrated the change of magnetic state by means of light irradiation from spin glass to a ferrimagnet over a wide range of temperatures below 290 K. The direct photoexcitation of spins with photon energy in the visible-light region (1.7-3.2 eV), which corresponds to the spin excitation energy of crystal field for Fe ions located in both tetrahedral and octahedral sites, is effective for realizing photoinduced magnetization. (C) 2000 American Institute of Physics. [S0021-8979(00)05601-8].

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  • Preparation and thickness dependence of magnetic properties of (111)-oriented Mg1.5FeTi0.5O4 spinel films on sapphire by pulsed laser deposition technique Reviewed

    Y Muraoka, K Ueda, H Tabata, T Kawai

    VACUUM   59 ( 2-3 )   622 - 627   2000.11

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    Thin films of (1 1 1)-oriented Mg1.5FeTi0.5O4 spinel have been successfully prepared by a pulsed laser deposition (PLD) technique on alpha -Al2O3 (0001) substrates. The value of the lattice parameter of the (1 1 1) out-of-plane and the Neel temperature of the films depend on the film thickness. The spin-glass behavior has been observed with a freezing temperature of 100 K, which is 80 K higher than that of the bulk material. This freezing temperature is reduced by increasing the oxygen pressure during film preparation. These results show that the PLD technique is promising not only for obtaining thin films of oxide materials under a wide range of conditions but also for controlling the magnetic properties of films. (C) 2000 Elsevier Science Ltd. All rights reserved.

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  • HRTEM and Micro-Raman Studies on Superconducting−Superionic Conducting Nanohybrid, Ag1.17I1.54Bi2Sr2CaCu2Oy Reviewed

    Jin-Ho Choy, Young-Il Kim, Seong-Ju Hwang, Yuji Muraoka, Naoyuki Ohnishi, Kenji Hiraga, Pham V. Huong

    The Journal of Physical Chemistry B   104 ( 39 )   9086 - 9090   2000.10

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  • Consolidation of Bi-Sr-Ca-Cu-O superconductors by the shock-loading method Reviewed

    M Kikuchi, H Faqir, S Kawamata, K Okuda, Y Muraoka, K Fukuoka, Y Syono

    SUPERCONDUCTOR SCIENCE & TECHNOLOGY   13 ( 8 )   1151 - 1154   2000.8

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    Shock compaction experiments were carried out for Bi2223 to prepare a dense, oriented bulk specimen. The shocked specimen exhibited a high degree of crystallographic orientation and a high density, above 96%. The optimal condition of the crystallographic orientation was attained at a shock pressure of 5 GPa and at annealing temperatures between 750 and 800 degrees C. The post annealing of a specimen shocked at 5 GPa was effective in increasing Delta M, indicating the introduction of pinning sites. The magnetic torque measurements showed that a high degree of orientation was attained and many pinning centres were induced by the shock loading.

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  • Photocontrol of spin-glass state in Mg1.5FeTi0.5O4 spinel ferrite films Reviewed

    Y Muraoka, H Tabata, T Kawai

    APPLIED PHYSICS LETTERS   76 ( 9 )   1179 - 1181   2000.2

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    A spin-glass state up to 210 K has been found in (Mg, Fe){Mg,Fe,Ti}(2)O-4 spinel ferrite thin films formed on alpha-Al2O3(0001) substrates. The films exhibit long-time relaxation of the magnetization in zero-field-cooled operation below 210 K; also, the ac susceptibility measurements show the presence of frequency-dependent cusp temperature. Both of the above observations are characteristic features of a spin glass. The change of magnetic state in the films from a spin glass to ferrimagnet has been achieved over a wide temperature range below 160 K by means of light irradiation. (C) 2000 American Institute of Physics. [S0003-6951(00)04209-1].

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  • Preparation of alpha-MnO2 with an open tunnel Reviewed

    Y Muraoka, H Chiba, T Atou, M Kikuchi, K Hiraga, Y Syono, S Sugiyama, S Yamamoto, JC Grenier

    JOURNAL OF SOLID STATE CHEMISTRY   144 ( 1 )   136 - 142   1999.4

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    A single-phase alpha-MnO2 without any large stabilizing cations was successfully prepared by starting from hollandite-type (NH4)(x)Mn8O16 and quenching from 440 degrees C during heating in flowing Ar. The unit-cell dimension was determined by XRD analysis to be a 10.308(2) Angstrom and c = 2.854(1) Angstrom. In comparison with that of the starting material (a = 9.896(1) Angstrom and c = 2.859(1) Angstrom), the a dimension increased while the c dimension changed little. No presence of ammonium ions in the structure of this specimen was shown by IR spectroscopy, the Kjeldahl analysis, or temperature-programmed-desorption (TPD) measurement. The structural change from the hollandite phase to Mn2O3 was observed at 540 degrees C. TPD analysis indicates the presence of nitrogen other than ammonium ions in the hollandite material we prepared, and also suggests that this nitrogen might have a strong chemical interaction to the hollandite structure, (C) 1999 Academic Press.

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  • Preparation of hexagonal MoO3 by "Chimie Douce" reaction with NO2 Reviewed

    Y Muraoka, JC Grenier, S Petit, M Pouchard

    SOLID STATE SCIENCES   1 ( 2-3 )   133 - 148   1999.3

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    The metastable hexagonal form of MoO3 has been successfully prepared starting from the ammonium molybdate, using a "Chimie Douce" reaction with NO2 gas. The lattice parameters of the as-prepared material were determined by XRD analysis to be : a = 10.633(2) Angstrom, and c = 3.719(1) Angstrom. The composition of this material obtained by physical and chemical analysis is MoO3, 0.09 H2O, showing that a small amount of water molecules remained while there were no more ammonium ions in this structure. The structural transformation from hexagonal to stable orthorhombic alpha-MoO3 phase was observed at 350 degrees C. It was also shown that NO2 reaction is a very useful method to remove topotactically ammonium ions from a parent structure at low temperature. This "Chimie Douce" process appears to be very promising for obtaining new metastable oxides with large tunnels or interlayer distances.

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  • New synthetic routes for preparing perovskites - Electrochemical oxidation and oxidation by NO2 Reviewed

    JC Grenier, JP Doumerc, Y Muraoka, S Petit, M Pouchard, A Wattiaux

    SOLID STATE IONICS   108 ( 1-4 )   9 - 15   1998.5

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    Two new synthetic low temperature routes for preparing perovskite-related materials, especially metastable phases are depicted. The first one, the electrochemical oxidation, uses the electric field as the driving force for intercalating oxygen atoms within parent oxide networks. The reaction is achieved under anodic potential, in alkaline solution (1 M KOH or NaOH), at room temperature, in air. This process has been used for preparing various perovskite compounds such as AMO(3) (A = Sr, La; M = Fe1-x Co-x) or A(2)MO(4+delta) (A = La, Nd, Sr). The most relevant results are reported. Potentiostatic and galvanostatic experiments have shown that the amount of intercalated oxygen can be controlled and that the process is reversible. Structural as well as electronic aspects of the oxygen intercalation are discussed and a reaction mechanism is proposed. The second route is based on the exothermic reaction of nitrogen dioxide NO2 with NH4+ ions at moderate temperatures (typically T < 300 degrees C), which allowed the destruction of NH4+ cations in situ. Topotactic reactions are described for preparing new hexagonal forms of WO3 or MoO3. The reaction process is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0167-2738(98)00012-5

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  • New "chimie douce" oxidizing processes: Electrochemical oxidation and in situ oxidation by NO2 Reviewed

    Jean-Claude Grenier, Jean-Pierre Doumerc, Yuji Muraoka, Stephane Petit, Michel Pouchard, Alain Wattiaux, Fang Zhou

    Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals   311   359 - 366   1998

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    Two new oxidation processes are described : the electrochemical oxidation in alkaline solution uses the electrical potential as the driving force for intercalating oxygen, at room temperature, into oxide networks such as perovskites or Ln2MO4 (M = Ni, Cu) compounds. The second one is based on the in situ destruction of ammonium ions in oxide lattices by interaction with NO2 gas, at moderate temperatures. Pictures of the reaction mechanisms are also proposed. © 1993 OPA (Overseas Publishers Association) Amsterdam B.V. Published under license under the Gordon and Breach Science Publishers imprint.

    DOI: 10.1080/10587259808042411

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  • Growth of high-quality Bi2Sr2CaCu2Oz crystal and characterization Reviewed

    H Faqir, G Vacquier, H Chiba, M Kikuchi, Y Muraoka, Y Syono

    JOURNAL OF MATERIALS RESEARCH   12 ( 10 )   2522 - 2525   1997.10

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    We report growth of high-quality Bi2Sr2CaCu2Oz single crystals with dimensions 2 x 1 x 0.03 mm(3) with a melt and growth technique. The composition of this crystal is homogeneous and very close to the stoichiometric composition. Structure characterization of a single crystal was realized by measuring the (001) x-ray diffraction. The lattice parameters of a typical crystal are a = 5.414(2) Angstrom, b = 5.413(2) Angstrom, and c = 30.823(10) Angstrom. The superconducting temperature T-c = 95 K with a sharp transition width (10-90% level) between 6 and 10 K was determined from resistivity and de susceptibility. We have measured the magnetization of Bi2Sr2CaCu2Oz single crystal under magnetic field applied along the c-axis. The anomalous second peak effect appeared between 20 and 30 K. We discuss the qualities of these crystals.

    DOI: 10.1557/JMR.1997.0334

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  • Ferromagnetism and large negative magnetoresistance in Bi1-xCaxMnO3 (x>=0.8) perovskite Reviewed

    H Chiba, M Kikuchi, K Kusaba, Y Muraoka, Y Syono

    SOLID STATE COMMUNICATIONS   99 ( 7 )   499 - 502   1996.8

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    Polycrystalline perovskite manganites Bi1-xCaxMnO3 (x greater than or equal to 0.8) have been prepared by standard ceramic technique, and their magnetic and electronic property are examined down to 5 K. Ferromagnetic moment and reduced resistivity are observed for Bi1-xCaxMnO3 (x greater than or equal to 0.875), and also large negative magnetoresistances appear below T-c. Copyright (C) 1996 Elsevier Science Ltd

    DOI: 10.1016/0038-1098(96)00305-5

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  • AgI-intercalation into Bi2Sr2CaCu2Oz compound Reviewed

    Y Muraoka, N Ohnishi, M Nagoshi, Y Morioka, M Kikuchi, K Hiraga, N Kobayashi, Y Syono

    PHYSICA C   263 ( 1-4 )   193 - 196   1996.5

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    Polycrystalline AgI-intercalated Bi2Sr2CaCu2Oz is prepared and the structure and physical properties studied. The lattice parameters a and c are determined to be 5.40 and 22.8 Angstrom, respectively. The expansion of the lattice parameter c is 7.4 Angstrom, compared with that of a Bi2Sr2CaCu2Oz (Bi2212) specimen (c/2: 15.4 Angstrom). This expansion is more than twice as large as that of iodine-intercalation (3.6 Angstrom). The EPMA measurement shows that the I/Ag ratio in the AgI-intercalated specimen is greater than 1.0. The T-c is 69 K, which is lower than that of Bi2212 (75 K) and almost the same as that of IBi2Sr2CaCu2Oz (IBi2212, 67 K). The effect of AgI-intercalation on the superconductivity is discussed.

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  • Synthesis conditions and superconductivity of Pb0.7Cu0.3Sr2Y0.5Ca0.5Cu2Oy Reviewed

    M Kikuchi, M Shida, E Ohshima, Y Muraoka, Y Syono

    PHYSICA C   263 ( 1-4 )   204 - 207   1996.5

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    Pb0.7Cu0.3Sr2Y0.5Ca0.5Cu2Oy was synthesized as a mother specimen in air and then annealed under two different experimental conditions, in an oxidizing and in a reducing condition. The mother specimen was a nonsuperconductor, but both annealed specimens, one quenched from high temperature and the other treated in high-pressure O-2, were superconductors with T-c's of about 50 K and about 60 K, respectively. The low Cu-valence of the quenched specimen which showed superconductivity suggests a decrease in the Pb-valence, while the high T, of the specimen treated in high-pressure O-2 would be explained by high Cu-valence and Pb4+.

    DOI: 10.1016/0921-4534(95)00824-1

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  • STRUCTURE AND SUPERCONDUCTIVITY OF IODINE-INTERCALATED BI2SR4CU2CO3OZ Reviewed

    Y MURAOKA, H NAMEKI, M KIKUCHI, S AWAJI, N KOBAYASHI, Y SYONO

    PHYSICA C   233 ( 1-2 )   209 - 213   1994.11

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    Iodine intercalation of a bismuth oxycarbonate, Bi2Sr4Cu2CO3Ox was successfully made. Expansion along the c-axis due to intercalation was estimated to be 3.6 Angstrom per half of the c-dimension in the host material, showing that a stage-1 compound was yielded. Interestingly, the semiconductor host material became superconducting with T-c = 23 K due to intercalation. This result tan be explained as hole doping from the intercalated iodine to the CuO2 sheet of the pristine compound.

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  • SYNTHESIS AND SUPERCONDUCTIVITY OF HG2CL2-INTERCALATED BI2SR2CAN-1CUNOZ (N=1-3) COMPOUNDS Reviewed

    Y MURAOKA, M KIKUCHI, N OHNISHI, N KOBAYASHI, K HIRAGA, Y SYONO

    PHYSICA C   233 ( 3-4 )   247 - 252   1994.11

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    We have found that 'Hg2Cl2' can be intercalated into Bi2Sr2Can-1CunOz (n=1-3) superconductors. Intercalated phases were examined by X-ray powder diffraction, electron diffraction, energy dispersive X-ray (EDX) analysis and magnetometry. The expansion along the c-axis upon intercalation was estimated to be about 3.5 Angstrom for n=1-3 specimens. The presence of both Hg and Cl atoms was confirmed by EDX analysis. The intercalated phase with tetragonal symmetry for n=1 has a superstructure of three times the perovskite unit along the a-axis, and has kept the staggered stacking of the basic building blocks of the host sample. The superconductivity of the n=2 phase is also described.

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  • SYNTHESIS AND SUPERCONDUCTIVITY OF OXYCARBONATES OF THE TL-1201 PHASE Reviewed

    M KIKUCHI, E OHSHIMA, N OHNISHI, Y MURAOKA, S NAKAJIMA, E AOYAGI, M OGAWA, J AKIMITSU, T OKU, K HIRAGA, Y SYONO

    PHYSICA C   219 ( 1-2 )   200 - 204   1994.1

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    TlBaxSr4-xCu2(CO3)Oy oxycarbonates with the Tl-1201 structure were synthesized over a wide range of x (1.0 less-than-or-equal-to x less-than-or-equal-to 3.2) and examined by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy and magnetometry methods. New phases with the Tl-1201 structure having 6 and 7 times periodicities along the b-axis were isolated. The former was stable for a wide Ba-rich range (1.8 less-than-or-equal-to x less-than-or-equal-to 3.2), and the latter was observed for a smaller Ba content range (1.2 less-than-or-equal-to x less-than-or-equal-to 1.6). The phase stability was found to depend on the synthesis condition. The maximum T(c) of the as-synthesized specimen in this series occurred at about 70 K around x = 2.0. The Meissner volume fraction of the as-synthesized specimen (x = 2.4) was 30% at 5 K.

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  • EFFECTS OF IODINE INTERCALATION ON THE SUPERCONDUCTING PROPERTIES OF THE BI2SR2-XLAXCUOZ COMPOUND Reviewed

    Y MURAOKA, M KIKUCHI, H NAMEKI, S AWAJI, R SUZUKI, N KOBAYASHI, Y SYONO

    PHYSICA C   215 ( 3-4 )   402 - 406   1993.10

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    Iodine intercalation of Bi2Sr2-xLaxCuOx (0.4 less-than-or-equal-to x less-than-or-equal-to 1.0) was studied. Transition from orthorhombic pristine phase to tetragonal intercalated phase was observed due to iodine intercalation. The expansion of the c-axis of the stage-1 intercalation compound increases slightly with increasing La content x. The T(c) of iodine-intercalated specimens with 0.4 less-than-or-equal-to x less-than-or-equal-to 0.6 decreases from that of the pristine, but in the range of 0.7 less-than-or-equal-to x less-than-or-equal-to 0.9, the T(c) of the intercalated specimen increases with respect to that of the pristine phase. Especially, the non-superconducting specimen with x = 0.9 became superconducting due to intercalation. This result demonstrates hole doping by iodine intercalation, i.e. the Cu valence of the pristine compound is increased.

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  • STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF IODINE-INTERCALATED BI2SR2CA1-XYXCU2OZ Reviewed

    Y MURAOKA, M KIKUCHI, N OHNISHI, K HIRAGA, R SUZUKI, N KOBAYASHI, Y SYONO

    PHYSICA C   204 ( 1-2 )   65 - 70   1992.12

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    The structual and superconducting properties of Bi2Sr2Ca1-xYxCu2Oz intercalated with iodine between the Bi-O bilayers were studied. Formation of the stage-1 compound was verified by X-ray analysis, TG analysis and TEM observation. Expansion of the c-axis, which is caused by increase in the distance of the BiO-BiO layers, decreases with decreasing intercalated iodine concentration down to 60%. The expansion of the c-axis of fully intercalated compounds increases with increasing Y content from 7.2 angstrom for x = 0 to 7.5 angstrom for x = 1.O. The temperature dependence of resistivity showed that iodine-doped samples (x = 0 and 0.4) were more semiconductive than non-doped samples. The T(c) of the IBi2Sr2Ca1-xYxCu2Oz series in the over-doped region was reduced by 2-10 K compared with non-intercalated samples.

    DOI: 10.1016/0921-4534(92)90573-U

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MISC

  • Local structure analysis of NaNiO2 by EXAFS

    脇田高徳, 密岡拓心, SIMONELLI Laura, MARINI Carlo, 秋光正子, 堀金和正, 秋光純, 溝川貴司, 村岡祐治, 横谷尚睦, SAINI Naurang L.

    日本物理学会講演概要集(CD-ROM)   75 ( 1 )   2020

  • Ti-15V-7Al 合金の低温と高温で形成されるマルテンサイト変態 Reviewed

    竹元嘉利, 恒川弥佑, 真鍋侑司, 板野壮志, 村岡祐治

    日本金属学会誌   82 ( 8 )   307 - 313   2018

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  • EXAFSによるキャリアドープSr2IrO4の局所結晶構造解析

    寺嶋健成, SALAS E., SIMONELLI L., PARIS E., JOSEPH B., 脇田高徳, 藤井政徳, 堀金和正, 小林夏野, 小林夏野, 堀江理恵, 秋光純, 村岡祐治, 村岡祐治, SAINI N. L., 横谷尚睦, 横谷尚睦

    日本物理学会講演概要集(CD-ROM)   73 ( 1 )   2018

  • Angle-resolved photoemission study on (Sr,La)2IrO4

    TERASHIMA Kensei, SUNAGAWA Masonori, FUJIWARA Hirokazu, HORIGANE Kazumasa, FUJII Masanori, HORIE Rie, KOBAYASHI Kaya, AKIMITSU Jun, ONO Kanta, KUMIGASHIRA Hiroshi, MURAOKA Yuji, YOKOYA Takayoshi

    KEK Progress Report (Web)   ( 2018-7 )   2018

  • 10aAS-7 PEEM observation of Ag micro-films on Si surfaces

    Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   69 ( 2 )   675 - 675   2014.8

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  • 9pBJ-7 Soft X-ray photoemission study of CeO_xF_<1-x>BiS_2

    Hamada T., Sonoyama J., Fujiwara H., Demura S., Okazaki H., Takano Y., Mizuguchi Y., Miura O., Kobayashi M., Horiba K., Kumigashira H., Okada K., Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   69 ( 2 )   443 - 443   2014.8

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  • 9pBJ-11 Electrical resistivity measurements of vacuum-evaporated K-doped picene films

    Hamada T., Jabuchi T., Okazaki H., Wakita T., Kambe T., Goto H., Kubozono H., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   69 ( 2 )   444 - 444   2014.8

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  • 8pBD-4 Preparation and electrical resistivity of a single-phase TaO_2 thin film

    Muraoka Yuji, Fujimoto Yuki, Wakita Takanori, Yokoya Takayoshi

    Meeting abstracts of the Physical Society of Japan   69 ( 2 )   387 - 387   2014.8

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  • 9pAJ-10 Bulk sensitive spin-resolved photoemission spectroscopy studies on CrO_2

    Fujiwara H., Sunagawa M., Kittaka T., Terashima K., Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   69 ( 2 )   532 - 532   2014.8

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  • 9pBD-12 Angle-Resolved Photoemission Spectroscopy on K_xFe_<2-y>Se_2

    Sunagawa M., Terashima K., Hamada K., Fujiwara H., Tanaka M., Takeya H., Takano Y., Arita M., Shimada K., Namatame H., Taniguchi M., Kuroki K., Suzuki K., Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   69 ( 2 )   437 - 437   2014.8

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  • 28pBE-6 Electronic structure of BiS_2 superconductors studied by soft X-ray ARPES

    Sonoyama J., Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   69 ( 1 )   628 - 628   2014.3

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  • 30aCM-9 Change of T_c due to crystallinity in superconducting diamond

    Okazaki H., Wakita T., Sonoyama J., Hamada T., Kittaka T., Muraoka Y., Yokoya T., Muro T., Nakamura T., Kurihara S., Kawarada H., Yamaguchi T., Takeya H., Takano Y.

    Meeting abstracts of the Physical Society of Japan   69 ( 1 )   675 - 675   2014.3

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  • 30pAP-1 Thermal diffusion process of Ag-micro films on Si surfaces

    Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   69 ( 1 )   907 - 907   2014.3

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  • Fermi surface nesting of ametallic VO_2 thin film

    Muraoka Yuji, Nagao Hiroshi, Wakita Takanori, Yokoya Takayoshi, Kumigasira Hiroshi, Oshima Masaharu

    Meeting abstracts of the Physical Society of Japan   68 ( 2 )   563 - 563   2013.8

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  • Angle-Resolved Photoemission Spectroscopy on La and P co-doped CaFe_2As_2 II

    Sunagawa M., Jabuchi M., Sonoyama J., Fujiwara H., Iba K., Kudo K., Nohara M., Ono K., Kumigashira H., Arita M., Shimada K., Namatame H., Taniguchi M., Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   68 ( 2 )   496 - 496   2013.8

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  • Conductivity and electronic state of K doped picene film

    Jabuchi T., Wakita T., Kubozono Y., Kambe T., Kato T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   68 ( 2 )   763 - 763   2013.8

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  • PEEM observation of Ag-micro films on Si surfaces

    Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   68 ( 2 )   827 - 827   2013.8

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  • Soft X-ray photoemlssion spectroscopy of novel BIS_2-based layered superconductors

    Sonoyama J., Nagira S., Sunagawa M., Otsuka T., Kittaka T., Hamada T., Muro T., Kumigashira H., Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   68 ( 2 )   586 - 586   2013.8

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  • ARPES study of heavily B-doped superconducting diamond with T_c of 25K

    Okazaki H., Wakita T., Sonoyama J., Hamada T., Kittaka T., Muraoka Y., Yokoya T., Muro T., Nakamura T., Kurihara S., Kawarada H., Yamaguchi T., Takeya H., Takano Y.

    Meeting abstracts of the Physical Society of Japan   68 ( 2 )   440 - 440   2013.8

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  • 26pXF-3 Electronic structure of doped aromatic hydrocarbon-based superconductor

    Jabuchi T., Wakita T., Kato T., Kubozono Y., Kambe T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   68 ( 1 )   907 - 907   2013.3

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  • 27aXZA-1 Thermal diffusion of Ag-micro films on Si surfaces

    Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   68 ( 1 )   986 - 986   2013.3

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  • 26aXG-8 Angle-Resolved Photoemission Spectroscopy on La and P co-doping of CaFe_2As_2

    Sunagawa M., Ishiga T., Tsubota K., Jabuchi T., Sonoyama J., Nagira S., Iba K., Kudo K., Nohara M., Ono K., Kumigashira H., Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   68 ( 1 )   574 - 574   2013.3

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  • 21aFE-3 Electronic structure of CeT_2Al_<10> (T= Fe, Ru, Os) studied by high-resolution photoemission spectroscopy III

    Ishiga T., Tsubota K., Sunagawa M., Uenaka K., Yutani K., Muro Y., Takabatake T., Kumigashira H., Oshima M., Okada K., Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   572 - 572   2012.8

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  • 18pFN-6 Microscopic observation of Ag micro-films on Si surfaces

    Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   818 - 818   2012.8

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  • 20aFJ-1 Angle-resolved photoemission spectroscopy for metallic VO_2 thin films

    Nagao H., Muraoka Y., Ishiga T., Tsubota K., Wakita T., Yokoya T., Ono K., Kumigashira H.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   696 - 696   2012.8

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  • 20aFG-8 Photoemission spectroscopy measurements of metallic VO_2 thin films induced by photo-irradiation

    Muraoka Y., Nagao H., Wakita T., Yokoya T., Kumigashira H., Oshima M.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   498 - 498   2012.8

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  • 19aGB-2 Photoemission spectroscopy of new superconductor SrPt_2As_2

    Sonoyama J., Wakita T., Yoshida R., Ishiga T., Thubota K., Hiramatsu C., Jabuchi T., Sunagawa M., Fujimoto Y., Nishikubo Y., Kudo K., Nohara M., Muro T., Izumi Y., Kumigashira H., Ono K., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   477 - 477   2012.8

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  • 19aFH-12 K doping dependent electronic structure of picene thin films

    Jabuchi T., Okazaki H., Wakita T., Kato T., Kubozono Y., Kanbe T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   773 - 773   2012.8

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  • 20aGA-12 Angle-resolved photoemission spectroscopy study of collapsed tetragonal phase in Ca(Fe_<1-x>Rh_x)_2As_2

    Tsubota K., Wakita T., Nagao H., Hiramatsu C., Ishiga T., Ono K., Danura M., Kudo K., Nohara M., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   503 - 503   2012.8

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  • 20aGA-13 Angle-Resolved Photoemission Spectroscopy of Ca_<10>(Pt_4As_8)(Fe_<2-x>Pt_xAs_2)_5

    Nagao H., Yoshida R., Tsubota K., Ishiga T., Jabuchi T., Sonoyama J., Kakiya S., Mitsuoka D., Kudo K., Nohara M., Jiang J., Iwasawa H., Shimada K., Namatame H., Taniguchi M., Ono K., Kumigashira H., Oshima M., Wakita T., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   503 - 503   2012.8

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  • 25pYB-3 Ultrahigh-Resolution Three-Dimensional ARPES on URu_2Si_2

    Yoshida R., Tsubota K., Ishiga T., Aoki D., Flouquet J., Varykhalov A., Rienks E., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   637 - 637   2012.3

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  • 27pYA-6 Photoemission study of K_xFe_<2-y>Se_2

    Fukui M., Tsubota K., Ishiga T., Yoshida R., Muro T., Takeya H., Takano Y., Hirai M., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   696 - 696   2012.3

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  • 27aYH-14 Surface physical property of CrO_2 thin films prepared using a closed chemical vapor deposition method

    Muraoka Y., Yoshida S., Wakita T., Hirai M., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   694 - 694   2012.3

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  • 27pYB-2 Electronic structure of CeT_2Al_<10>(T=Fe, Ru, Os) studied by high-resolution photoemission spectroscopy II

    Ishiga T., Yoshida R., Nakamura Y., Tsubota K., Yutani K., Muro Y., Takabatake T., Kumigashira H., Oshima M., Hirai M., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   698 - 698   2012.3

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  • 25pCK-7 PEEM study of thermal diffusion of Ag micro-films on Si surfaces

    Wakita T., Hirai M., Muraoka Y., Yokoya T.

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   950 - 950   2012.3

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  • Surface physical property of the CrO 2 thin films prepared using a closed chemical vapor deposition method Reviewed

    Y. Muraoka, S. Yoshida, T. Wakita, M. Hirai, T. Yokoya

    Materials Research Society Symposium Proceedings   1406   17 - 22   2012

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    We have examined the intrinsic surface physical property of a CrO 2 thin film by means of surface sensitive photoemission spectroscopy. Epitaxial thin film of CrO 2(100) has been grown on TiO 2(100) by a closed chemical vapor deposition method using a Cr 8O 21 precursor. Low-energy electron diffraction (LEED) observations find that epitaxial growth of rutile-phase CrO 2 occurs to the top monolayer of the film. Surface sensitive x-ray photoemission spectroscopy (XPS) measurements show a finite intensity in the region of the Fermi energy. The result evidences that the physical nature of near topmost layer of CrO 2 thin film is metallic. Progress of understanding of the surface physical property of CrO 2 thin film helps not only perform a reliable photoemission study to understand the physics of ferromagnetic metal in CrO 2, but also develop the CrO 2-based devices using a half-metallic nature for spintronics applications. © 2012 Materials Research Society.

    DOI: 10.1557/opl.2012.177

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  • Preparation of the CrO2 thin films using a Cr8O 21 precursor Reviewed

    Y. Muraoka, K. Iwai, S. Yoshida, T. Wakita, M. Hirai, T. Yokoya, Y. Kato, T. Muro, Y. Tamenori

    Materials Research Society Symposium Proceedings   1292   87 - 92   2011

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    We have prepared a CrO2 thin film by chemical vapor deposition from a Cr8O21 precursor and studied the bulk and surface physical properties. The CrO2 thin film is grown on TiO 2(100) substrate by heating precursor and TiO2 (100) substrate together in a sealed quartz tube. The prepared film is found from x-ray diffraction analysis to be an (100)-oriented single phase. The magnetization and resistivity measurements indicate that the film is a ferromagnetic metal with a Curie temperature of about 400 K. Cr 3s core-level and valence band photoelectron spectroscopy spectra reveal the presence of a metallic CrO2 in the surface region of the film. Our work indicates that preparation from a Cr8O21 precursor in a closed system is promising for obtaining a CrO2 thin film with the metallic surface. © 2011 Materials Research Society.

    DOI: 10.1557/opl.2011.154

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  • 光ドーピングで制御する強相関物性 Reviewed

    村岡祐治, 広井善二

    パリティ   20   52 - 55   2005

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  • 遷移金属酸化物へテロ接合における光キャリア注入 Reviewed

    広井善二, 村岡祐治, 村松孝樹, 山内徹, 山浦淳一

    固体物理   39   211 - 224   2004

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  • Strain effects on the metal-insulator transition in VO2 thin films

    Muraoka Yuji, Hiroi Zenji

    Meeting abstracts of the Physical Society of Japan   57 ( 2 )   421 - 421   2002.8

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  • 25pYJ-1 Crystal and electronic structures of Cd_2Re_2O_7

    Hiroi Z., Yamaura J., Hanawa M., Yonezawa S., Muraoka Y.

    Meeting abstracts of the Physical Society of Japan   57 ( 1 )   561 - 561   2002.3

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  • 25pWA-4 VO_2薄膜の光電子分光(25pWA その他(光電子分光,薄膜,電界効果など),領域8(強相関系分野-高温超伝導,強相関f電子系など))

    岡崎 浩三, 櫃田 幸央, 溝川 貴司, 藤森 淳, 小野田 雅重, 小高 秀文, 榎本 幹子, 重里 有三, 村岡 祐治, 廣井 善二

    日本物理学会講演概要集   57 ( 1 )   549 - 549   2002.3

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  • Effects of iodine intercalation on the structural and superconducting properties of Bi2Sr2-xLnxCuOz (Ln=Nd and Sm) compound

    Y. Muraoka, M. Kikuchi, M. Hiroi, N. Kobayashi, K. Hiraga, Y. Syono

    Advances in Superconductivity   XI   431 - 434   1999

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  • "Creation of Novel Properties on Ferromagnetic・Ferroelectric Superlattices" 共著

    Transaction of the Materials Research Society of Japan   24 ( 1 )   13 - 18   1999

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  • 31P-YD-10 Magnetic And Electric Propert y of Bi_<1-x>CaxMnO_3

    Chiba H., Muraoka Y., Kusaba K., Kikuchi M., Syono Y.

    Abstracts of the meeting of the Physical Society of Japan. Annual meeting   51 ( 3 )   44 - 44   1996.3

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Presentations

  • Spinodal decomposition in rurtile-type TiO2-RuO2 films

    Yuji Muraoka, Takumi Kawahara, Takanori Wakita, Takayoshi Yokoya, Toshito Takemoto

    2021.9.12 

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  • Spinodal decomposition in TiO2-RuO2 epitaxial films

    Yuji Muraoka, Takumi Kawahara, Takanori Wakita, Takayoshi Yokoya, Yoshito Takemoto

    2021.7.31 

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  • Spinodal decomposition in Ti0.2V0.8O2/TiO2(100)

    Yuji Muraoka, Takahiro Fukuda, Takanori Yokoya, Shintaro Sugitate, Syotaro Miyazaki, Yoshito Takemoto

    2021.3.19 

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    Event date: 2021.3.16 - 2021.3.21

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  • Characterization of sp3 content in amorphous carbon film

    Yuji Muraoka, Takanori Wakita, Takayoshi Yokoya

    The 25th Hiroshima International Symposium on Synchrotron Radiation  2021.3.4 

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    Event date: 2021.3.4 - 2021.3.5

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  • Formation of nanostructured films via spinodal decomposition in a TiO2-VO2 system Invited

    Y. Muraoka, T. Wakita, T. Yokoya, Y. Takemoto

    2020.12.10 

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    Event date: 2020.12.9 - 2020.12.11

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  • Preparation of Q-carbon by adjusting sp3 content in DLC films and laser energy density of pulsed laser annealing

    Y. Muraoka, H. Yoshinaka, S. Inubushi, T. Wakita, T. Yokoya

    2020.12.9 

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  • スピノーダル分解したTiO2-VO2系膜における格子歪とラメラ周期の関係

    村岡祐治, 福田貴優, 脇田高徳, 横谷尚睦, 竹元嘉利

    第81回応用物理学会 秋季学術講演会  2020.9.9 

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    Event date: 2020.9.8 - 2020.9.11

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  • sp3分率とレーザー密度をパラメータとしたQ-カーボンの作製

    村岡祐治, 芳中大樹, 犬伏聖子, 脇田高徳, 横谷尚睦

    第81回応用物理学会 秋季学術講演会  2020.9.8 

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  • sp3量とレーザー出力の調整によるQカーボンの作製

    村岡祐治, 芳中大樹, 犬伏聖子, 脇田高徳, 横谷尚睦

    2020年度 応用物理・物理系学会中国四国支部合同学術講演会  2020.8.2 

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  • TiO2-RuO2系膜における異方的スピノーダル分解発生の試み

    村岡祐治, 前川拓哉, 脇田高徳, 横谷尚睦, 竹元嘉利

    第67回応用物理学会 春季学術講演会  2020.3.13 

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  • Change in work function of VO2 at the metal-insulator transition in a VO2/TiO2:Nb(001) heterojunction International conference

    Yuji Muraoka, Yuki Suga, Hayato Nakahara, Takayoshi Yokoya

    International Conference on Strongly Correlated Electron Systems (SCES) 2019, Okayama Convention Center, Okayama, Japan,  2019.9.26 

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  • VO2/TiO2:Nb接合界面を活用したVO2薄膜の仕事関数の評価

    村岡祐治, 壽賀友貴, 脇田高徳, 横谷尚睦

    第80回応用物理学会 秋季学術講演会、北海道大学 札幌キャンパス  2019.9.18 

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  • VO2の薄膜作製について Invited

    村岡祐治

    日本表面真空学会 スパッタリングおよびプラズマプロセス技術部会 第162回定例研究会「酸化バナジウム薄膜の作製とその応用」  2019.9.13 

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  • ルチル型複合酸化物薄膜の作製と機能探索 Invited

    村岡祐治

    第69回 CVD研究会(第30回夏季セミナー)高知工科大学 永国寺キャンパス  2019.8.8 

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  • Ti0.4V0.6O2/TiO2(100)膜界面近傍のスピノーダル分解

    村岡祐治, 壽賀友貴, 寺嶋健成, 脇田高徳, 横谷尚睦

    2019年度 応用物理・物理系学会中国四国支部合同学術講演会 高知工科大学 香美キャンパス  2019.7.21 

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  • ARPES study on a metallic phase of VO2/TiO2(001) thin films International conference

    Yuji Muraoka, Hiroki Nagao, Yuichiro Yao, Takanori Wakita, Kensei Terashima, Takayoshi Yokoya, Hiroshi Kumigashira, Masaharu Oshima

    The 23th Hiroshima International Symposium on Synchrotron Radiation  2019.3.7 

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  • Formation of multilayer structure via spinodal decomposition in TiO2-VO2 epitaxial films Invited International conference

    Y. Muraoka, Y. Matsuura, Y. Takemoto, K. Terashima, T. Wakita, T. Yokoya

    The 2nd International Conference on Advanced Materials and Processes for Environment, Energy and Health, Holiday inn, Montreal, Canada  2018.10.31 

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  • TiO2-VO2系膜におけるスピノーダル分解と格子歪

    村岡祐治, 吉井文哉, 寺嶋健成, 脇田高徳, 横谷尚睦

    第79回応用物理学会 秋季学術講演会、名古屋国際会議場  2018.9.19 

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  • VO2薄膜金属相の電子状態

    村岡祐治

    第3回「表面界面の機能創製とデバイス応用」セミナー  2018.8.7 

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  • スピノーダル分解を用いたTiO2-VO2多層構造膜の作製

    村岡 祐治, 松浦 由佳, 真部 侑司, 鈴木 雄基, 荒木 稜, 門脇 賢司, 竹元 嘉利, 寺嶋健成, 脇田 高徳, 横谷 尚睦

    2018年度 応用物理・物理系学会中国四国支部合同学術講演会 広島大学東広島キャンパス  2018.8.4 

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  • TiO2-VO2系配向膜におけるスピノーダル分解

    村岡祐治, 松浦由佳, 真鍋侑司, 鈴木雄基, 荒木稜, 門脇賢司, 竹元利嘉, 寺嶋健成, 脇田高徳, 横谷尚睦

    第65回応用物理学会 春季学術講演会、早稲田大学 西早稲田キャンパス  2018.3.20 

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  • XPS study of boron-doped diamond films covered by V2O5 International conference

    Y. Muraoka, T. Wakita, T. Yokoya

    The 22th Hiroshima International Symposium on Synchrotron Radiation  2018.3.8 

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  • TiO2-VO2系におけるスピノーダル分解膜の作製 Invited

    村岡祐治

    第2回「表面界面の機能創製とデバイス応用」セミナー  2018.2.27 

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  • サファイア基板上へのTiO2-VO2系スピノーダル分解膜の作製

    村岡祐治, 松浦由佳, 門脇賢司, 井尻正孝, 竹元嘉利, 寺嶋健成, 脇田高徳, 横谷尚睦

    2017年度 第78回応用物理学会秋季学術講演会 福岡国際会議場・福岡国際センター・福岡サンパレス  2017.9.7 

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  • XPS study of TaO2 thin films International conference

    Y. Muraoka, Y. Fujimoto, M. Kameoka, Y. Matsuura, M. Sunagawa, K. Terashima, T. Wakita, T. Yokoya

    The 21th Hiroshima International Symposium on Synchrotron Radiation  2017.3.2 

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  • NbO2テンプレート層を用いた、PLD法によるTaO2薄膜の作製

    村岡祐治, 藤本佑樹, 亀岡美咲, 松浦由佳, 砂川正典, 寺嶋健成, 脇田高徳, 横谷尚睦

    第63回応用物理学会 春季学術講演会、東京工業大学 大岡山キャンパス  2016.3.22 

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  • TiO2-VO2系における異方的スピノーダル分解とその制御 Invited

    村岡祐治

    第76回応用物理学会 秋季学術講演会、名古屋国際会議場  2015.9.15 

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  • ルチル型 TiO2-VO2 系におけるスピノーダル分解 Invited

    村岡祐治

    第3回酸化物研究の新機軸に向けた学際討論会  2015.8.7 

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  • スピノーダル分解したTiO2-VO2系薄膜の作製

    村岡祐治, 大塚翼, 寺嶋健成, 脇田高徳, 横谷尚睦

    2015年度 応用物理・物理系学会中国四国支部合同学術講演会 徳島大学常三島キャンパス  2015.8.1 

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  • ホットフィラメントCVD法により作製した高濃度ホウ素ドープダイヤモンド超伝導膜のキャリア濃度とTcの関係

    村岡祐治, 橘高朋子, 犬伏聖子, 寺嶋健成, 脇田高徳, 横谷尚睦

    日本物理学会 第70回年次大会、早稲田大学 早稲田キャンパス  2015.3.22 

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  • (Ti0.4V0.6)O2薄膜のスピノーダル分解

    村岡祐治, 大塚翼, 寺嶋健成, 脇田高徳, 横谷尚睦

    第62回応用物理学会 春季学術講演会、東海大学 湘南キャンパス  2015.3.12 

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  • Preparation and characterization of single-phase TaO2 thin films International conference

    Yuji Muraoka, Yuki Fujimoto, Takanori Wakita, Takayoshi Yokoya

    Ushimado International Workshop on Physics and Chemistry of Novel Superconductors and Related Materials  2014.11.9 

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  • Preparation of a single-phase TaO2 thin film

    Yuji Muraoka, Yuki Fujimoto, Takanori Wakita, Takayoshi Yokoya

    2014.9.18 

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  • 単一相ルチル型TaO2薄膜の作製とその伝導特性

    村岡祐治, 藤本佑樹, 脇田高徳, 横谷尚睦

    日本物理学会 2014年秋季大会 中部大学 春日井キャンパス  2014.9.8 

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  • パルスレーザー堆積法による単一相TaO2薄膜の作製

    村岡祐治, 藤本佑樹, 脇田高徳, 横谷尚睦

    2014年度 応用物理・物理系学会中国四国支部合同学術講演会 島根大学松江キャンパス  2014.7.26 

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  • VO2薄膜における軟X線誘起絶縁体金属転移

    村岡祐治, 長尾浩樹, 脇田高徳, 横谷尚睦, 組頭広志, 尾嶋正治

    放射光科学による革新的イノベーションワークショップ  2014.3.14 

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  • Spin-resolved Photoemission Spectroscopy of CrO2 thin films International conference

    Y. Muraoka, M. Sunagawa, A. Mizutani, K. Miyamoto, T. Okuda

    The 18th Hiroshima International Symposium on Synchrotron Radiation  2014.3.6 

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  • VO2薄膜の金属相フェルミ面ネスティング

    村岡祐治, 長尾浩樹, 脇田高徳, 横谷尚睦, 組頭広志, 尾嶋正治

    日本物理学会 2013年秋季大会  2013.9.27 

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  • 低キャリア濃度で高Tcを示すホットフィラメントCVD法製ダイヤモンド超伝導膜

    村岡祐治, 平松千明, 脇田高徳, 横谷尚睦, 組頭広志, 尾嶋正治

    第74回応用物理学会秋季学術講演会  2013.9.18 

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  • Photocarrier injection to VO2 thin films Invited International conference

    Yuji Muraoka, Takanori Wakita, Takayoshi Yokoya

    2013 JSAP-MRS joint symposia  2013.9.17 

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  • ホットフィラメント法で作製した高濃度ホウ素ドープダイヤモンド超伝導膜におけるホウ素の化学状態

    村岡祐治, 平松千明, 脇田高徳, 横谷尚睦

    応用物理学会中国四国支部、日本物理学会中国支部、四国支部、2013年度支部学術講演会  2013.7.27 

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  • Photo-induced insulator to metal transition for VO2 thin films International conference

    Y. Muraoka, H. Nagao, T. Wakita, T. Yokoya

    The 17th Hiroshima International Symposium on Synchrotron Radiation  2013.2.28 

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  • Surface physical property of the CrO2 thin films International conference

    Y. Muraoka, S. Yoshida, T. Wakita, M. Hirai, T. Yokoya

    International Symposium on Physics and Chemistry of Novel Superconductors and Related Materials  2012.10.2 

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  • VO2薄膜における光誘起 絶縁体-金属転移とその電子状態の観測

    村岡祐治, 長尾浩樹, 脇田高徳, 横谷尚睦, 組頭広志, 尾嶋正治

    日本物理学会 2012年秋季大会  2012.9.20 

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  • Effectiveness of a closed CVD method for preparation of CrO2 thin films

    Y. Muraoka, S. Yoshida, T. Wakita, T. Yokoya, H. Kumugashira, M. Oshima

    2012.9.12 

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  • CrO2単結晶薄膜作製における閉鎖系化学気相法の利点

    村岡祐治, 吉田祥, 脇田高徳, 横谷尚睦

    応用物理学会中国四国支部、日本物理学会中国支部、四国支部  2012.7.28 

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  • VO2薄膜における放射光誘起絶縁体金属転移

    村岡祐治, 長尾浩樹, 脇田高徳, 横谷尚睦

    応用物理学会中国四国支部、日本物理学会中国支部、四国支部  2012.7.28 

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  • 閉鎖系化学気相法により作製したCrO2薄膜の表面特性

    村岡祐治, 吉田祥, 脇田高徳, 平井正明, 横谷尚睦

    日本物理学会 第67回年次大会  2012.3.27 

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  • CrO2薄膜の表面特性

    村岡祐治, 吉田祥, 脇田高徳, 平井正明, 横谷尚睦

    2012年春季 第59回応用物理学関係連合講演会  2012.3.17 

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  • 光照射によるVO2薄膜への電子キャリア注入

    村岡祐治, 長尾浩樹, 大山卓郎, 脇田高徳, 平井正明, 横谷尚睦

    2012年春季 第59回応用物理学関係連合講演会  2012.3.17 

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  • Metallic surface of the CrO2 thin films prepared using a closed chemical vapor deposition method International conference

    Y. Muraoka, S. Yoshida, M. Hirai, T. Wakita, T. Yokoya

    The 16th Hiroshima International Symposium on Synchrotron Radiation  2012.3.1 

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  • Surface physical property of the CrO2 thin films prepared using a closed chemical vapor deposition method International conference

    Y. Muraoka, S. Yoshida, T. Wakita, M. Hirai, T. Yokoya

    2011 Fall Meeting of the Materials Research Society  2011.11.28 

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  • 放射光照射によるVO2薄膜への電子キャリア注入

    村岡祐治, 長尾浩樹, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 為則雄祐

    日本物理学会 2011年秋季大会  2011.9.21 

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  • Preparation of NbO2 thin films using a pulsed laser deposition method

    Y. Muraoka, Y. Fujimoto, C. Hiramatsu, T. Wakita, M. Hirai, T. Yokoya

    2011.8.31 

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  • 低キャリア濃度で高Tcを示すホウ素ドープ超伝導ダイヤダイヤモンド膜の作製

    村岡祐治, 土居智彰, 平松千明, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 泉雄大, 為則雄祐

    2011年秋季 第72回応用物理学会学術講演会  2011.8.30 

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  • VO2薄膜における放射光照射効果

    村岡祐治, 片山晋輔, 長尾浩樹, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 泉雄大, 為則雄祐

    応用物理学会中国四国支部、日本物理学会中国支部、四国支部  2011.7.30 

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  • ホットフィラメントCVD法により作製したホウ素ドープダイヤモンド膜の超伝導特性

    村岡祐治, 土居智彰, 平松千明, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 泉雄大, 為則雄祐

    応用物理学会中国四国支部、日本物理学会中国支部、四国支部  2011.7.30 

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  • NbO2薄膜の作製とその電子状態

    村岡祐治, 平松千明, 平井正明, 横谷尚睦

    日本物理学会 第66回年次大会  2011.3.28 

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  • ホットフィラメントCVD法による超伝導ホウ素ドープダイヤダイヤモンド膜の作製

    村岡祐治, 土居智彰, 平井正明, 横谷尚睦

    2011年春季 第58回応用物理学関係連合講演会  2011.3.26 

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  • Angle resolved photoemission spectroscopy measurements of metallic VO2 thin films International conference

    Y. Muraoka, Y. Yao, T. Wakita, M. Hirai, T. Yokoya

    The 15th Hiroshima International Symposium on Synchrotron Radiation  2011.3.3 

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  • 機能性ルチル型酸化物薄膜の作製とその電子状態

    村岡祐治

    第10回琉球物性研究会  2010.12.10 

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  • Preparation of the CrO2 thin films using a Cr8O21 precursor International conference

    Y. Muraoka, K. Iwai, S. Yoshida, T. Wakita, M. Hirai, T. Yokoya, Y. Kato, T. Muro, Y. Tamenori

    2010 Fall Meeting of the Materials Research Society  2010.12.3 

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  • 閉鎖系化学気相成長法によりCr8O21原料から作製したCrO2薄膜のバルクおよび表面特性評価

    村岡祐治, 岩井啓介, 吉田祥, 脇田高徳, 平井正明, 横谷尚睦, 加藤有香子, 室隆桂之, 為則雄祐

    日本物理学会 2010年秋季大会  2010.9.24 

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  • Bulk and surface physical properties of the CrO2 thin films prepared from a Cr8O21 precursor International conference

    Y. Muraoka, K. Iwai, S. Yoshida, T. Wakita, M. Hirai, T. Yokoya, Y. Kato, T. Muro, Y. Tamenori

    17th International Workshop on Oxide Electronics  2010.9.21 

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  • 閉鎖系化学気相成長法により作製したCrO2薄膜のバルクおよび表面特性

    村岡祐治, 岩井啓介, 吉田祥, 平井正明, 横谷尚睦, 加藤有香子, 室隆桂之, 為則雄祐

    応用物理学会中国四国支部、日本物理学会中国支部、四国支部  2010.7.30 

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  • Synthesis and physical properties of the hollandite-type titanium oxide KxTi8O16 International conference

    Y. Muraoka, K. Noami, T. Wakita, M. Hirai, T. Yokoya, Y. Kato, T. Muro, Y. Tamenori

    The 37th International Symposium on Compound Semiconductors iscs2010  2010.5.31 

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  • Cr8O21を原料に用いたCrO2薄膜の作製とその表面特性

    村岡祐治, 岩井啓介, 脇田高徳, 平井正明, 横谷尚睦, 加藤有香子, 室隆桂之, 為則雄祐

    日本物理学会 第65回大会年次大会  2010.3.23 

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  • Preparation of surface metallic CrO2 thin films International conference

    Y. Muraoka, K. Iwai, S. Yoshida, T. Wakita, M. Hirai, T. Yokoya

    The 14th Hiroshima International Symposium on Synchrotron Radiation  2010.3.4 

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  • Band dispersion near the Fermi level for VO2 thin films grown on TiO2 (001) substrates International conference

    Y. Muraoka, K. Saeki, Y. Yao, T. Wakita, M. Hirai, T. Yokoya, R. Eguchi, S. Shin

    11th International Conference on Electronic Spectroscopy and Structure (ICESS-11)  2009.10.6 

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  • 表面まで金属特性を示すCrO2薄膜の作製

    村岡祐治, 岩井啓介, 脇田高徳, 平井正明, 横谷尚睦, 加藤有香子, 室隆桂之, 為則雄祐

    日本物理学会2009年秋季大会  2009.9.28 

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  • バーネサイト型MnO2におけるMnのスピン状態

    村岡祐治, 田嶋光俊, 脇田高徳, 平井正明, 横谷尚睦, 加藤有香子, 室隆桂之, 為則雄祐

    応用物理学会中国四国支部、日本物理学会中国支部、四国支部  2009.8.1 

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  • ホランダイト型マンガン酸化物(NH4)xMn8O16内に存在する窒素の役割

    村岡祐治, 田嶋光俊, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 為則雄祐

    2009年春季 第56回応用物理学関係連合講演会  2009.3.29 

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  • MnO2多形の光電子分光

    村岡祐治, 田嶋光俊, 脇田高徳, 平井正明, 横谷尚睦, 加藤有香子, 室隆桂之, 為則雄祐

    日本物理学会(第64回年次大会)  2009.3.29 

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  • Spin state of Mn ion in birnessite-type manganese dioxide International conference

    Y. Muraoka, M. Tajima, T. Wakita, M. Hirai, T. Yokoya, Y. Kato, T. Muro, Y. Tamenori

    The 13thHiroshima International Symposium on Synchrotron Radiation  2009.3.10 

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  • Research activity at Beamline 5 International conference

    Y. Muraoka, T. Wakita, M. Hirai, T. Yokoya

    The 13thHiroshima International Symposium on Synchrotron Radiation  2009.3.10 

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  • ホランダイト型チタン酸化物の合成と物性

    村岡祐治, 野網健悟, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 為則雄祐

    2008年秋季 第69回応用物理学会学術講演会  2008.9.2 

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  • ホランダイト型 チタン酸化物の合成、物性および電子状態

    村岡祐治, 野網健悟, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 為則雄祐

    応用物理学会中国四国支部、日本物理学会中国支部、四国支部  2008.8.2 

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  • VO2/TiO2界面の電子状態

    村岡祐治, 佐伯邦成, 江口律子, 辛埴, 横谷尚睦, 仙波泰徳, 大橋治彦

    2008年春季 第55回応用物理学関係連合講演会  2008.3.30 

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  • ホランダイト型マンガン酸化物(NH4)xMn8O16の合成と物性II

    村岡祐治, 田嶋光俊, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 為則雄祐

    日本物理学会(第63回年次大会)  2008.3.24 

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  • Recent activity at Beamline 5 International conference

    Y. Muraoka, T. Wakita, M. Hirai, T. Yokoya

    The 12thHiroshima International Symposium on Synchrotron Radiation  2008.3.13 

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  • ホランダイト型マンガン酸化物(NH4)xMn8O16の合成と物性

    村岡祐治, 田嶋光俊, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 為則雄祐

    日本物理学会(第62回年次大会)  2007.9.21 

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  • ホランダイト型 (NH4)xMn8O16の合成と物性

    村岡祐治, 田嶋光俊, 脇田高徳, 平井正明, 横谷尚睦, 室隆桂之, 為則雄祐

    応用物理学会中国四国支部、日本物理学会中国支部、四国支部  2007.8.4 

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  • 永続的光伝導を示すSnO2薄膜のガス応答性

    村岡祐治, 廣井善二

    2007年春季 第54回応用物理学関係連合講演会  2007.3.27 

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  • VO2薄膜における金属状態の膜厚依存性

    村岡祐治, 佐伯邦成, 江口律子, 仙波泰徳, 大橋治彦, 辛埴, 横谷尚睦

    日本物理学会(2007年春季大会)  2007.3.19 

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  • Current role at Beamline 5: Research of surface science and education International conference

    Y. Muraoka, T. Wakita, M. Hirai, T. Yokoya

    The 11thHiroshima International Symposium on Synchrotron Radiation  2007.3.8 

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  • Persistent photoconductivity in an SnO2 thin film International conference

    Y. Muraoka, Z. Hiroi

    2006.11.15 

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  • SnO2薄膜への光キャリア注入

    村岡祐治, 廣井善二

    2006年春季 第53回応用物理学会関係連合講演会  2006.3.23 

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  • SnO2薄膜における永続的光伝導

    村岡祐治, 廣井善二

    学術創成研究「新しい研究ネットワークによる電子相関系の研究」-物理学と化学の真の融合を目指してー  2006.1.30 

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  • ルチル型酸化物への光キャリア注入

    村岡祐治, 廣井善二

    特定領域研究「異常量子物質の創製」-新しい物理を生む新物質―  2005.12.19 

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  • 光で制御する遷移金属酸化物の物性 Invited

    村岡祐治, 廣井善二

    第137回日本金属学会  2005.9.29 

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  • YBa2Cu3Ox極薄膜への光キャリア注入

    村岡祐治, 村松孝樹, 廣井善二

    日本物理学会第60回年次大会  2005.3.24 

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  • Photocarrier injection to transition metal oxides International conference

    Y. Muraoka, T. Muramatsu, Z. Hiroi

    2005.3.15 

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  • 光電荷注入による遷移金属酸化物薄膜の物性制御 Invited

    村岡祐治, 村松孝樹, 廣井善二

    東北大学金研ワークショップ 「強相関酸化物の機能開発とコンビナトリアル手法の接点」  2005.1.13 

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  • Photogenerated carrier injection to transition metal oxides International conference

    Y. Muraoka, T. Muramatsu, Z. Hiroi

    2004 Materials Research Society Fall Meeting  2004.12.3 

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  • Photogenerated carrier injection to an n-type copper oxide superconductor International conference

    Y. Muraoka, T. Muramatsu, Z. Hiroi

    The 11th international workshop on oxide electronics  2004.10.3 

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  • (Sr,Nd)CuO2薄膜への光キャリア注入

    2004.9.12 

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  • 遷移金属酸化物への光キャリアドーピング

    村岡祐治, 村松孝樹, 廣井善二

    学術創成研究「新しい研究ネットワークによる電子相関系の研究」-物理学と化学の真の融合を目指してー  2004.7.7 

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  • REBa2Cu3O7-x/SrTiO3(100)(RE:希土類)における電気抵抗の光照射効果

    村岡祐治, 村松孝樹, 山浦淳一, 山内徹, 広井善二

    日本物理学会第59回年次大会  2004.3.27 

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  • Photogenerated hole carrier injection to transition metal oxides International conference

    Y. Muraoka, T. Muramatsu, J. Yamaura, T. Yamauchi, Z. Hiroi

    2004.1.19 

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  • 遷移金属酸化物への光キャリア注入

    村岡祐治, 広井善二

    日本応用磁気学会 第11回化合物新磁性材料専門研究会 「遷移金属元素を含む化合物の光応答」  2003.12.12 

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  • Efficient Photocarrier Injection to Transition Metal Oxides International conference

    Yuji Muraoka, Touru Yamauchi, Takaki Muramatsu, Jun-ichi Yamaura, Zenji Hiroi

    2003 Materials Research Society Fall Meeting  2003.12.1 

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  • 光による遷移金属酸化物の物性制御

    村岡祐治, 山内徹, 村松孝樹, 山浦淳一, 広井善二

    学術創成研究「新しい研究ネットワークによる電子相関系の研究」-物理学と化学の真の融合を目指してー  2003.10.9 

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  • YBa2Cu3O7-x薄膜への光キャリア注入

    村岡祐治, 村松孝樹, 山内徹, 山浦淳一, 広井善二

    日本物理学会秋季大会  2003.9.23 

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    Language:Japanese   Presentation type:Oral presentation (general)  

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  • Yuji Muraoka, Touru Yamauchi, Takaki Muramatsu, Jun-ichi Yamaura and Zenji Hiroi International conference

    Yuji Muraoka, Touru Yamauchi, Takaki Muramatsu, Jun-ichi Yamaura, Zenji Hiroi

    International Conference on Magnetism  2003.7.27 

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  • 薄膜への光キャリア注入 Invited

    村岡祐治, 村松孝樹, 山内徹, 山浦淳一, 広井善二

    第36回コンビナトリアルプロジェクト研究会  2003.6.24 

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    Language:Japanese   Presentation type:Oral presentation (invited, special)  

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  • 遷移金属酸化物への光キャリア注入1, 2

    村岡祐治, 山内徹, 村松孝樹, 山浦淳一, 広井善二

    2003年春季 第50回応用物理学会関連連合講演会  2003.3.28 

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  • Photocarrier injection I: Giant photoconductivity in transition metal oxides

    Y. Muraoka, T. Yamauchi, T. Muramatsu, J. Yamaura, Z. Hiroi

    2003.1.8 

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  • ルチル型機能性酸化物の作製 Invited

    村岡祐治

    第31回マテリアル・テーラリング研究会  2002.3.30 

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    Language:Japanese   Presentation type:Oral presentation (invited, special)  

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  • スピノーダル分解した(Ti,V)O2の構造と物性

    村岡祐治, 上田寛, 廣井善二

    2002年春季 第49回応用物理学関連連合講演会  2002.3.28 

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  • スピノーダル分解した(Ti,V)O2の構造と物性

    村岡祐治, 速水宏明, 上田寛, 廣井善二

    日本物理学会第57回年次大会  2002.3.25 

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  • ルチル型機能性酸化物の作製

    村岡祐治, 速水宏明, 上田寛, 廣井善二

    学術創成研究「新しい研究ネットワークによる電子相関系の研究」-物理学と化学の真の融合を目指してー  2002.2.12 

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    Language:Japanese   Presentation type:Oral presentation (general)  

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  • Large modification of the metal-insulator transition temperature in strained VO2 films grown on TiO2 substrates International conference

    Yuji Muraoka, Yutaka Ueda, Zenji Hiroi

    2001.11 

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  • VO2 - TiO2系におけるスピノ-ダル分解とその物性

    村岡祐治, 速水宏明, 広井善二

    日本物理学会秋季大会  2001.9.19 

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  • TiO2基板を用いたVO2の金属絶縁体転移温度の制御

    村岡祐治, 廣井善二

    2001年秋季 第62回応用物理学会学術講演会  2001.9.11 

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  • VO2薄膜およびVO2-TiO2スピノーダル系における金属絶縁体転移

    村岡祐治, 速水宏明, 廣井善二

    東京大学物性研究所短期研究会「遷移金属酸化物の化学」  2001.1.6 

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  • PrBa2Cu3Ozバルク体および薄膜の合成と物性

    村岡祐治, 廣井善二

    日本物理学会第55回年次大会  2000.9.23 

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  • スピネルMg1.4Fe1.2Ti0.4O4薄膜における室温スピングラス的振る舞いとその光制御

    村岡祐治, 田畑仁, 川合知二

    2000年春季 第47回応用物理学関係連合講演会  2000.3.31 

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Industrial property rights

  • 転移温度が制御された部材

    Hiroi Zenji, Muraoka Yuji

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    Application no:特願2001-182190 

    Announcement no:特開2003-002791 

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  • 高温スピングラスを有し、また光によりスピン制御可能なスピネル型フェライト薄膜およびその製造方法

    川合知二, 田畑仁, 村岡祐治

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    Application no:特願2000-035119 

    Announcement no:特開2001-230117 

    Patent/Registration no:特許4139882 

    6,488,908 B1 (米国)

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Works

  • Method of prepring High temperature spin-glass and to photo-controlable spinel-type ferrito films.

    1999

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Awards

  • 応用物理学会 講演奨励賞

    2000  

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    Country:Japan

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Research Projects

  • Development of heavily impurity doped Q-carbon high-Tc superconductor by an adjusted pulsed laser annealing technique

    Grant number:21H01624  2021.04 - 2024.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    Yuji Muraoka

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    Authorship:Principal investigator 

    Grant amount:\16900000 ( Direct expense: \13000000 、 Indirect expense:\3900000 )

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  • Development of the carbon-based bendable super-hard material

    2020.04 - 2021.03

    岡山工学振興会  一般研究助成 

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    Authorship:Principal investigator 

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  • 高出力太陽電池を指向した、スピノーダル分解による超多層ルチル型酸化物膜の開発

    2017.04 - 2020.03

    MEXT/JSPS  KAKENHI 

    MURAOKA Yuji

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    Authorship:Principal investigator  Grant type:Competitive

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  • 強相関電子物性が制御可能な光キャリア注入法の確立

    2014.04 - 2017.03

    MEXT/JSPS  KAKENHI 

    MURAOKA Yuji

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    Authorship:Principal investigator  Grant type:Competitive

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  • 光キャリア注入による金属酸化物の物性制御

    2011.04 - 2014.03

    MEXT/JSPS  KAKENHI 

    MURAOKA Yuji

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    Authorship:Principal investigator  Grant type:Competitive

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  • スピノーダル分解を用いた新規ルチル型機能性酸化物の作製

    2002.04 - 2005.03

    MEXT/JSPS  KAKENHI 

    MURAOKA Yuji

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    Authorship:Principal investigator  Grant type:Competitive

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Other research activities

  • 国際共同研究

    1998
    -
    1999

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    フランスCNRS ボルドー固体化学研究所と多孔質物質作製に関する共同研究を行った。

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Class subject in charge

  • Information Physics Experiments 2 (2021academic year) 3rd and 4th semester  - 月5,月6,月7,月8

  • Information Physics Experiments 2 (2021academic year) 3rd and 4th semester  - 月5,月6,月7,月8

  • Solid-state Synchrotron Spectroscopy (2021academic year) Prophase  - 火3,火4

  • Synchrotron Material Science Course (2021academic year) Concentration  - その他

  • Physics for General Education (Mechanics) 1 (2021academic year) Third semester  - 月1~2

  • Physics for General Education (Mechanics) 2 (2021academic year) Fourth semester  - 月1~2

  • 物理学実験3 (2021academic year) 通年  - 木曜日・5~8限

  • Physics Experiments 2 (2021academic year) 3rd and 4th semester  - [第3学期]月5,月6,月7,月8, [第4学期]月4,月5,月7,月8

  • 物理科学入門A (2021academic year) 第3学期  - 火曜日・3、4限

  • 物理科学入門B (2021academic year) 第4学期  - 火曜日・3、4限

  • Seminar in Physics of Solid Surfaces and Interfaces (2021academic year) Year-round  - その他

  • 自然科学入門1 (2021academic year) 第1学期  - 火曜日・3、4限

  • 自然科学入門2 (2021academic year) 第2学期  - 火曜日・3、4限

  • 自然科学特論 (2021academic year) 第2学期  - 水曜日・7、8限

  • Physical Properties of thin films (2021academic year) Late  - その他

  • Information Physics Experiments 2 (2020academic year) 3rd and 4th semester  - 月3,月4,月5,月6

  • Information Physics Experiments 2 (2020academic year) 3rd and 4th semester  - 月3,月4,月5,月6

  • Solid-state Synchrotron Spectroscopy (2020academic year) Prophase  - 火1,火2

  • Synchrotron Material Science Course (2020academic year) Concentration  - その他

  • Physics for General Education (Mechanics) 1 (2020academic year) Third semester  - 月1,月2

  • Physics for General Education (Mechanics) 2 (2020academic year) Fourth semester  - 月1,月2

  • Physics Experiments 2 (2020academic year) 3rd and 4th semester  - 月3,月4,月5,月6

  • Seminar in Physics of Solid Surfaces and Interfaces (2020academic year) Year-round  - その他

  • Physical Properties of thin films (2020academic year) Late  - その他

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Social Activities

  • さくらサイエンス

    Role(s):Lecturer, Planner, Organizing member, Demonstrator

    岡山大学  先端物質科学実習  2019.2.17 - 2019.2.24

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    Type:Other

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Media Coverage

  • 人工ダイヤよりも硬い「Qカーボン」 新炭素材 国内初作製 Newspaper, magazine

    山陽新聞  2020.8.22

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  • 炭素材料Qカーボンの作製に成功 岡大グループ 人工ダイヤ代替期待 Internet

    山陽新聞digital  https://www.sanyonews.jp/article/1043899  2020.8.21

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  • 炭素材料Qカーボンの作製に成功 岡大グループ 人工ダイヤ代替期待 Internet

    NewNewNews  https://newnewnews.info/669531895461512289/  2020.8.21

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  • 炭素材料Qカーボンの作製に成功 岡大グループ 人工ダイヤ代替期待 Internet

    ORICON NEWS  https://www.oricon.co.jp/article/1251919/  2020.8.21

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  • 超強磁場で金属化 Newspaper, magazine

    日刊工業新聞  2020.8.18

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  • 二酸化バナジウム、超強磁場で金属化 東大・岡山大が発見 Internet

    日刊工業新聞オンライン  https://www.nikkan.co.jp/articles/view/568093  2020.8.18

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  • Okayama University succeeds in producing Q-carbon with laser Internet

    OPTRONICS ONLINE  https://optronics-media.com/news/20200731/66656/  2020.7.31

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  • 強相関電子の絶縁性をスピンで制御 二酸化バナジウム、強磁場で絶縁体から金属に変化 Internet

    EE Times Japan  https://eetimes.itmedia.co.jp/ee/articles/2007/22/news021.html  2020.7.22

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  • 東大ら、磁場による強相関絶縁体の金属化を発見 Internet

    OPTRONICS ONLINE  https://optronics-media.com/news/20200720/66301/  2020.7.22

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  • The University of Tokyo et al. Discovered metallization of strongly correlated insulators by magnetic field Internet

    OPTRONICS ONLINE  https://optronics-media.com/news/20200720/66301/  2020.7.20

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Academic Activities

  • 表面界面の機能創製とデバイス応用セミナー

    Role(s):Planning, management, etc.

    村岡祐治  2018.8.7

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  • 応用物理学会・物理系学会中国四国支部 合同学術講演会

    Role(s):Planning, management, etc.

    応用物理学会・物理系学会中国四国支部  2016.7.31

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    Type:Academic society, research group, etc. 

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  • 日本磁気学会専門研究会 化合物新磁性材料専門研究会

    Role(s):Planning, management, etc.

    日本磁気学会専門研究会  2003.4 - 2006.3

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    Type:Academic society, research group, etc. 

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  • 1) 学術創成研究「新しい研究ネットワークによる電子相関系の研究―物理学と化学の真の融合を目指して―若手の会

    Role(s):Planning, management, etc.

    代表 茅 幸ニ  2001.4 - 2006.3

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    Type:Academic society, research group, etc. 

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