論文 - 村岡　祐治

Local-structure insight into the improved superconducting properties of Pb-substituted La(O, F)BiS2: a photoelectron holography study 査読

YaJun Li, Yusuke Hashimoto, Noriyuki Kataoka, Zexu Sun, Sota Kawamura, Hiroto Tomita, Taro Setoguchi, Soichiro Takeuchi, Shunjo Koga, Kohei Yamagami, Yoshinori Kotani, Satoshi Demura, Kanako Noguchi, Hideaki Sakata, Tomohiro Matsushita, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

Scientific Reports   15 ( 1 )   8366 - 8366   2025年3月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-025-86233-2

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その他リンク： https://www.nature.com/articles/s41598-025-86233-2

First-principles calculations concerning ferromagnetism in Q-carbon 査読

Qiang Yue, Takayoshi Yokoya, Yuji Muraoka

Diamond and Related Materials   151   111807 - 111807   2025年1月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.diamond.2024.111807

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Effects of thermal energy on the formation of lattice strain in VO2 thin films grown on TiO2(001) 査読

Reki Nakamoto, Hiroyuki Okazaki, Takanori Wakita, Takayoshi Yokoya, Yuji Muraoka

Langmuir   40 ( 46 )   24447 - 24454   2024年11月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.langmuir.4c03004

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Reversible modulations of insulator–metal transition in an epitaxial VO2 film through thermal crystallization and femtosecond laser-induced-amorphization of capping Ge2Sb2Te5 layer 査読

Takuto Ohnuki, Kunio Okimura, Yiqi Liu, Shoya Inagaki, Yuji Muraoka, Joe Sakai, Aiko Narazaki, Masashi Kuwahara

Journal of Applied Physics   136 ( 8 )   085305   2024年8月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0211742

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First-principles molecular dynamics simulations for the properties of boron-doped tetrahedral amorphous carbon 査読

Qiang Yue, Takayoshi Yokoya, Yuji Muraoka

Diamond and Related Materials   143   110894   2024年2月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.diamond.2024.110894

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Modulation of insulator metal transition of VO₂ films grown on Al2O3 (001) and TiO2 (001) substrates by the crystallization of capping Ge2Sb2Te5 layer 査読

Takuto Ohnuki, Kunio Okimura, Reki Nakamoto, Yuji Muraoka, Joe Sakai, Masashi Kuwahara

134 ( 24 )   245302   2023年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0176810

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Molecular dynamics simulation of deposition of amorphous carbon films on sapphire surfaces 査読

Qiang Yue, Takayoshi Yokoya, Yuji Muraoka

Diamond and Related Materials   140   110514   2023年12月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.diamond.2023.110514

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Photoelectron holographic evidence for the incorporation site of Se and suppressed atomic displacement of the conducting layer of La(O,F)BiSSe 査読

YaJun Li, ZeXu Sun, Noriyuki Kataoka, Taro Setoguchi, Yusuke Hashimoto, Soichiro Takeuchi, Shunjo Koga, Kazuhisa Hoshi, Yoshikazu Mizuguchi, Tomohiro Matsushita, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

62 ( 12 )   125001 - 125001   2023年11月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.35848/1347-4065/ad079b

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その他リンク： https://iopscience.iop.org/article/10.35848/1347-4065/ad079b/pdf

Photoelectron Holography Study of La(O,F)BiS₂ 査読

YaJun Li, ZeXu Sun, Noriyuki Kataoka, Taro Setoguchi, Yusuke Hashimoto, Soichiro Takeuchi, Shunjo Koga, Satoshi Demura, Kanako Noguchi, Hideaki Sakata, Yoshikazu Mizuguchi, Tomohiro Matsushita, Takanori Wakita, Yuji Muraoka, Takayoshi Yokoya

Journal of the Physical Society of Japan   92 ( 4 )   044801   2023年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7566/jpsj.92.044801

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Self-organized vertical multilayer structures in spinodally decomposed TiO2-VO2 films on glass substrates 査読

Yuji Muraoka, Kazutada Takeda, Yoshito Takemoto, Takanori Wakita, Takayoshi Yokoya

Thin Solid Films   769   139749 - 139749   2023年3月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.tsf.2023.139749

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Magnetic-Field-Induced Insulator Metal Transition of W-doped VO2 Observed by Electromagnetic Flux Compression at ISSP 査読

Yasuhiro H. Matsuda, Yuji Muraoka, Daisuke Nakamura, Akihiko Ikeda, Yuto Ishii, Xu-Guang Zhou, Hironobu Sawabe, Shojiro Takeyama

J. Phys. Soc. Jpn.   91 ( 10 )   101008   2022年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7566/JPSJ.91.101008

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Anomalously large spin-dependent electron correlation in the nearly half-metallic ferromagnet CoS2 査読

Hirokazu Fujiwara, Kensei Terashima, Junya Otsuki, Nayuta Takemori, Harald O. Jeschke, Takanori Wakita, Yuko Yano, Wataru Hosoda, Noriyuki Kataoka, Atsushi Teruya, Masashi Kakihana, Masato Hedo, Takao Nakama, Yoshichika Ōnuki, Koichiro Yaji, Ayumi Harasawa, Kenta Kuroda, Shik Shin, Koji Horiba, Hiroshi Kumigashira, Yuji Muraoka, Takayoshi Yokoya

Physical Review B   106 ( 8 )   085114   2022年8月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/physrevb.106.085114

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.106.085114/fulltext

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

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年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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 査読

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

Thin Solid Films   751   139210   2022年4月

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担当区分：最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.tsf.2022.139210

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Soft x-ray irradiation induced metallization of layered TiNCl 査読

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年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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その他リンク： https://iopscience.iop.org/article/10.1088/1361-648X/abbbc3/pdf

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

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

Nature Communications   11 ( 1 )   3591   2020年12月

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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その他リンク： 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 査読

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

Carbon   167   504 - 511   2020年10月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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 査読

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年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

Yuji Muraoka, Yuki Suga, Hayato Nakahara, Takayoshi Yokoya

JPS Conf. Proc.   30   011071 - 011071   2020年3月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1088/1361-648x/abbbc3

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-648X/abbbc3/pdf

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

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

698   137854   2020年2月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

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年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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高濃度ホウ素ドープダイヤモンドの高分解能光電子ホログラフィー(Ⅲ)

細田 渉, 寺嶋 健成, 藤原 弘和, 矢野 佑幸, 片岡 範行, 谷口 拓海, 松下 智裕, 室 隆桂之, 木下 豊彦, 高野 義彦, 蔭浦 泰資, 川原 田洋, 小口 多美夫, 脇田 高徳, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   75.1   2060 - 2060   2020年

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.75.1.0_2060

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

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年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7566/jpsj.88.104709

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

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 ( 9 )   5915 - 5919   2019年

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.nanolett.9b01481

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Enhanced thermoelectricity by controlled local structure in bismuth-chalcogenides 査読

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年

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.5087096

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Origins of Thermal Spin Depolarization in Half-Metallic Ferromagnet CrO2 査読

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年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/physrevlett.121.257201

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その他リンク： 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 査読

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年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

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 査読

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

Mater. Trans.   59   1560 - 1566   2018年

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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 査読

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

Sci. Rep.   8   17906   2018年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-018-36281-8

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

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年

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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 査読

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年

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/c8cp03756f

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Temperature-dependent local structure and superconductivity of BaPd2As2 and SrPd2As2 査読

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年

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.98.094525

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Megagauss-field effect on the metal-insulator transition in V(1-x)WxO(2) (x=0.06) 査読

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

2018 16TH INTERNATIONAL CONFERENCE ON MEGAGAUSS MAGNETIC FIELD GENERATION AND RELATED TOPICS (MEGAGAUSS)   107 - 110   2018年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Effects of ultrahigh magnetic fields on the electronic state of V1-xWxO2 (x=0.06) are investigated. Optical transmission increases with decreasing temperature due to the transformation from the high-temperature metallic state to the low-temperature insulating state. We have made optical transmission measurements with 2 mu m wavelength laser light, and found that the low-temperature insulating state is suppressed by ultrahigh magnetic fields exceeding around 100 T.

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Martensitic transformation induced at low and high temperatures on Ti-15V-7Al alloy

Yoshito Takemoto, Miyu Tsunekawa, Yuji Manabe, Soushi Itano, Yuji Muraoka

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   82 ( 8 )   307 - 313   2018年

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japan Institute of Metals (JIM)  

Martensitic transformation behavior during cooling and heating of Ti-15V-7Al was investigated. The alloy was heated at 1050°C under a vacuum and quenched into an iced water. The structure of the quenched specimen consist of most β-phase and a small quantity of α" martensite at near grain boundaries. The elastic bent strip using a jig exhibited spontaneous shape change into the bending direction with heating. By sub zero treatment using LN2, some martensites were newly formed at around prior martensites formed by quench, but no martensite was formed at the single region. The martensite formation by the sub zero treatment exhibited a time dependence. Even tempering at 550°C for a few second dramatically induced coarse martensites all over the specimen. All martensites, formed by the quenching, the sub zero treatment, or the tempering, disappeared completely by the heat treatment at 200°C for 300 s, and turned into a single β phase. However, the coarse martensites were regenerated again from the single β phase by the tempering at 550°C for a short time, which means the martensite behavior in the range of 200∼550°C is reversible. Continuous isothermal aging at 550°C led to a remarkable hardening through the process of β → coarse α" fine α → β+ fineα. Both the Ms curve and the free energy model with a spinodal decomposition of α which can explain the martensite formation at low and high temperatures, were proposed.

DOI： 10.2320/jinstmet.J2018014

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

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年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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) 査読

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年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ROYAL SOC CHEMISTRY  

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 査読

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年8月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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 査読

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

Phys. Rev. B   96 ( 4 )   041106(R)   2017年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.96.041106

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Electronic structure of K-doped picene film on HOPG 査読

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

JOURNAL OF PHYSICS-CONDENSED MATTER   29 ( 6 )   26672 - 26678   2017年2月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

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 査読

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年

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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 査読

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年9月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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 査読

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年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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 査読

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年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.93.235129

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

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

599   125 - 132   2016年1月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.tsf.2015.12.066

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

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年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IOP PUBLISHING LTD  

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) 査読

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

J. Phys.: Conf. Ser.   683   012002   2016年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1088/1742-6596/683/1/012002

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19aBP-1 熱電変換物質SnSeの角度分解光電子分光

永山 貴将, 寺嶋 健成, 田中 将嗣, 小木曽 理, 高野 義彦, 森 仁志, 臼井 秀知, 黒木 和彦, 脇田 高徳, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   71   1441 - 1441   2016年

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_1441

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19pAJ-1 ハーフメタルCrO_2(001)膜表面の金属性

藤原 弘和, 砂川 正典, 寺嶋 健成, 永山 貴将, 橘高 朋子, 尾形 誠, 出田 真一郎, 田中 清尚, 脇田 高徳, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   71   2492 - 2492   2016年

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_2492

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21pBN-6 Sr_<2-x>La_xIrO_4の角度分解光電子分光

寺嶋 健成, 濱田 貴裕, 砂川 正典, 藤原 弘和, 藤井 政徳, 堀金 和正, 小林 夏野, 堀江 理恵, 秋光 純, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   71   2315 - 2315   2016年

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_2315

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

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

APPLIED PHYSICS LETTERS   106 ( 20 )   202404   2015年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

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.

DOI： 10.1063/1.4921629

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Comparative ARPES Study on Iron–Platinum–Arsenide Superconductor Ca10(Pt4As8)(Fe2−xPtxAs2)5 (x = 0.25 and 0.42) 査読

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

J. Phys. Soc. Jpn.   84 ( 5 )   055001   2015年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7566/JPSJ.84.055001

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

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年2月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

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.

DOI： 10.1063/1.4907411

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

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

Appl. Phys. Lett.   2015年2月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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18pCH-1 バルク敏感スピン分解光電子分光による強磁性金属CrO_2 の本質的な電子状態の解明

藤原 弘和, 砂川 正典, 寺嶋 健成, 橘高 朋子, 尾形 誠, 脇田 高徳, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   70   942 - 942   2015年

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.2.0_942

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16pDA-7 Ln(O,F)BiS_2におけるフェルミ面形状と化学圧力効果 : 角度分解光電子分光

寺嶋 健成, 脇田 高徳, 砂川 正典, 藤原 弘和, 濱田 貴裕, 長尾 雅則, 綿打 敏司, 田中 功, 小野 寛太, 組頭 広志, 岡崎 宏之, 高野 義彦, 臼井 秀知, 黒木 和彦, 鈴木 雄大, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   70   1720 - 1720   2015年

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.2.0_1720

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16aDB-6 K_xFe_<2-y>Se_2の角度分解光電子分光II

砂川 正典, 寺嶋 健成, 濱田 貴裕, 藤原 弘和, 福良 哲司, 竹田 彩, 田中 将嗣, 竹屋 浩幸, 高野 義彦, 有田 将司, 島田 賢也, 生天目 博文, 谷口 雅樹, 鈴木 雄大, 臼井 秀知, 黒木 和彦, 脇田 高徳, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   70   1681 - 1681   2015年

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.2.0_1681

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16aAD-4 複鉄酸化物YbFe_2O_4のFe 3p-3d共鳴光電子分光

福良 哲司, 脇田 高徳, 竹田 彩, 寺嶋 健成, 藤原 孝将, 池田 直, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   70   2405 - 2405   2015年

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.2.0_2405

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17pCD-9 Ce(Os_<1-y>Re_y)_2Al_<10>の高分解能光電子分光

永山 貴将, 寺嶋 健成, 川端 丈, 山田 義大, 高畠 敏郎, 脇田 高徳, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   70   1933 - 1933   2015年

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.2.0_1933

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18aCE-9 高濃度ボロンドープダイヤモンド超伝導のB1s-2p共鳴光電子分光

竹田 彩, 脇田 高徳, 福良 哲司, 高野 義彦, 栗原 慎一郎, 川原田 洋, 小口 多美夫, 村岡 祐治, 横谷 尚睦

日本物理学会講演概要集   70   1237 - 1237   2015年

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.2.0_1237

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

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

90 ( 22 )   220512(R)   2014年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/physrevb.90.220512

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その他リンク： 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 査読

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年9月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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 &lt; Os &lt; 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.

DOI： 10.7566/JPSJ.83.094717

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

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年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.7566/JPSJ.83.063708

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

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

53 ( 5 )   05FB09   2014年5月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/JJAP.53.05FB09

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

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年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.89.205114

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

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年3月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

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.

DOI： 10.1038/srep04381

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

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年3月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.7566/JPSJ.83.033703

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

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

PHYSICAL REVIEW B   88 ( 24 )   245414   2013年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.88.245414

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

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年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.7566/JPSJ.82.073705

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Spinodal Decomposition in the TiO2-VO2 System 査読

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

CHEMISTRY OF MATERIALS   25 ( 11 )   2202 - 2210   2013年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

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.

DOI： 10.1021/cm400236p

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

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年

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1038/srep02750

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Te concentration dependent photoemission and inverse-photoemission study of FeSe1-xTex 査読

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年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL INST MATERIALS SCIENCE  

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.

DOI： 10.1088/1468-6996/13/5/054403

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

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年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.86.014521

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

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年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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 査読

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年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.85.241102

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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 査読

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

25   5 - 7   2012年5月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.diamond.2012.02.008

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Photoemission Study of Rh17S15 Superconductor 査読

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年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJS.80SA.SA111

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

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年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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 査読

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年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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&apos;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.

DOI： 10.1016/j.jpcs.2010.10.048

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Multiple phosphorus chemical sites in heavily phosphorus-doped diamond 査読

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年2月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

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]

DOI： 10.1063/1.3554699

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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 査読

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

109 ( 4 )   043702   2011年2月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3549835

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

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

8 ( 2 )   555 - 557   2011年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1002/pssc.201000383

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

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年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IOP PUBLISHING LTD  

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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Electronic Structure of the Novel Filled Skutterudite PrPt4Ge12 Superconductor 査読

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年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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 -&gt; 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

DOI： 10.1143/JPSJ.79.124701

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Photoemission study of Ca-intercalated graphite superconductor CaC6 査読

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年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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 査読

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

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   470   S641 - S643   2010年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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 査読

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年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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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Signature of hidden order and evidence for periodicity modification in URu2Si2 査読

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年11月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.82.205108

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

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年11月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.82.195114

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

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

181 ( 2-3 )   249 - 251   2010年8月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.elspec.2010.02.003

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

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

108 ( 4 )   043916   2010年8月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3471811

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Room temperature ferromagnetic behavior in the hollandite-type titanium oxide 査読

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

107 ( 7 )   073910   2010年4月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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 査読

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

APPLIED SURFACE SCIENCE   256 ( 4 )   948 - 949   2009年11月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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.

DOI： 10.1016/j.apsusc.2009.05.120

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

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

80 ( 12 )   125406   2009年9月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.80.125406

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Bulk-sensitive spectroscopic studies on noncentrosymmetric superconducting system of Mg–Ir–B 査読

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年8月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.physc.2009.05.175

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The electronic structure of Ca-intercalated superconducting graphite CaC6 査読

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年8月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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.

DOI： 10.1016/j.physc.2009.05.172

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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 査読

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年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.80.035420

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Photoinduced conductivity in tin dioxide thin films 査読

Y. Muraoka, N. Takubo, Z. Hiroi

105 ( 10 )   103702   2009年5月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3126713

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Conductivity Switching by Ultraviolet Light in Tin Dioxide Thin Films 査読

Naoko Takubo, Yuji Muraoka, Zenji Hiroi

APPLIED PHYSICS EXPRESS   2 ( 4 )   045501   2009年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOCIETY APPLIED PHYSICS  

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

DOI： 10.1143/APEX.2.045501

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

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年3月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.78.034703

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

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年3月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.78.034708

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

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年3月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.78.034705

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Effect of UV light irradiation in SnO2 thin film 査読

Naoko Takubo, Yuji Muraoka, Zenji Hiroi

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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IOP PUBLISHING LTD  

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.

DOI： 10.1088/1742-6596/148/1/012025

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Fully gapped superconductivity and strong electron correlations in the -pyrochlore KOs2O6 査読

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

J. Phys. Chem.Solids   69 ( 12 )   3228 - 3231   2008年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jpcs.2008.06.058

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

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年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.77.104701

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

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年8月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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).

DOI： 10.1103/PhysRevB.78.075115

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Preparation and characterization of epitaxial Fe(2-x)Ti(x)O(3) films with various Ti concentrations (0.5 &lt; x &lt; 1.0) 査読

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

104 ( 3 )   033713   2008年8月

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.2966298

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Full-gap superconductivity with strong electron correlations in the -pyrochlore KOs2O6 査読

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

Physica B   403 ( 5-9 )   1068 - 1070   2008年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.physb.2007.10.090

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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 査読

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

APPLIED SURFACE SCIENCE   254 ( 1 )   26 - 28   2007年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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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Interplay of superconductivity and rattling phenomena in -pyrochlore KOs2O6 studied by photoemission spectroscopy 査読

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

Phys. Rev. Lett.   99 ( 11 )   117003   2007年9月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.99.117003

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Photoemission study of TiO2/VO2 interfaces 査読

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年9月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.76.115121

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

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年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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 (&gt;= 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.

DOI： 10.1143/JPSJ.76.063703

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Precise control of band filling in NaxCoO2 査読

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年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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 &lt;= x &lt;= 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 &gt; x*.

DOI： 10.1143/JPSJ.76.063705

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

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年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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.

DOI： 10.1016/j.elspec.2006.12.055

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NMR observation of rattling phonons in the pyrochlore superconductor KOs2O6 査読

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

PHYSICAL REVIEW LETTERS   98 ( 19 )   197002   2007年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevLett.98.197002

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Impurity effects on the Ni3+ triangular lattice of Ag2NiO2 査読

H. Yoshida, Y. Muraoka, Z. Hiroi

JOURNAL OF PHYSICS-CONDENSED MATTER   19 ( 14 )   145234   2007年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

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 &lt;= x &lt;= 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.

DOI： 10.1088/0953-8984/19/14/145235

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NMR study of -pyrochlore oxide superconductor KOs2O6 査読

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

J. Magn. Magn. Mater.   310 ( 2 )   698 - 699   2007年3月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/jmmm.2006.10.186

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Electronic structure of VO2/TiO2 : Nb upon photocarrier injection 査読

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

PHYSICAL REVIEW B   75 ( 7 )   073102   2007年2月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.75.073102

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Asakura et al. reply

D. Asakura, J. W. Quilty, K. Takubo, T. Mizokawa, T. Mizokawa, Y. Muraoka, Z. Hiroi

Physical Review Letters   97   2006年9月

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DOI： 10.1103/PhysRevLett.97.119702

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

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

PHYSICAL REVIEW LETTERS   96 ( 24 )   247004   2006年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

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 -&gt; 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.

DOI： 10.1103/PhysRevLett.96.247004

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High-pressure effects on the superconductivity on -pyrochlore oxides AOs2O6 査読

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

Physica B   378-80   882 - 883   2006年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.physb.2006.01.323

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NMR studies of -pyrochlore superconductors with osmium, under hydrostatic pressure 査読

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

Physica B   378-80   878 - 879   2006年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.physb.2006.01.322

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Upper critical field of -pyrochlore KOs2O6 single crystal 査読

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

J. Phys. Soc. Jpn.   75 ( 4 )   045002   2006年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JPSJ.75.045002

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

K Okazaki, S Sugai, Y Muraoka, Z Hiroi

PHYSICAL REVIEW B   73 ( 16 )   165116   2006年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.73.165116

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Crystal structure of the pyrochlore oxide superconductor KOs2O6 査読

JI Yamaura, S Yonezawa, Y Muraoka, Z Hiroi

JOURNAL OF SOLID STATE CHEMISTRY   179 ( 1 )   336 - 340   2006年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE  

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.

DOI： 10.1016/j.jssc.2005.10.039

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

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

PHYSICAL REVIEW B   73 ( 2 )   020408(R)   2006年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.73.020408

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Spin-1/2 triangular laiftice in Ag2NiO2 査読

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

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

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：AMER INST PHYSICS  

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.

DOI： 10.1063/1.2355083

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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年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：AMER INST PHYSICS  

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.

DOI： 10.1063/1.2355148

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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年12月

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記述言語：英語   出版者・発行元：INSTITUTE OF PURE AND APPLIED PHYSICS  

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年12月

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記述言語：英語   出版者・発行元：INSTITUTE OF PURE AND APPLIED PHYSICS  

DOI： 10.1143/JPSJ.74.3399

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Photocarrier-injected electronic structure of VO2/TiO2 : Nb 査読

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

APPLIED PHYSICS LETTERS   87 ( 20 )   201912   2005年11月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

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.

DOI： 10.1063/1.2132078

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

T Muramatsu, Y Muraoka, Z Hiroi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS   44 ( 10 )   7367 - 7371   2005年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

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).

DOI： 10.1143/JJAP.44.7367

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Anomalous pressure dependence of the superconducting transition temperature of -pyrochlore AOs2O6 oxides 査読

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

Phys. Rev. Lett.   95 ( 16 )   167004   2005年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.95.167004

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Photocarrier injection to organic compounds 査読

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

Synthetic Metals   152 ( 1-3 )   385 - 388   2005年9月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.synthmet.2005.07.115

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Photogenerated carrier injection to an n-type copper oxide superconductor 査読

Y Muraoka, T Muramatsu, Z Hiroi

486 ( 1-2 )   82 - 85   2005年8月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.tsf.2004.11.212

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Second anomaly in the specific heat of -pyrochlore oxide superconductor KOs2O6 査読

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

J. Phys. Soc. Jpn.   74 ( 6 )   1682 - 1685   2005年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JPSJ.74.1682

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Photoemission study of YBa2Cu3Oy thin films under light illumination 査読

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年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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.

DOI： 10.1016/j.elspec.2005.01.134

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

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年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.74.1678

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

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

PHYSICA B-CONDENSED MATTER   359   488 - 490   2005年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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.

DOI： 10.1016/j.physb.2005.01.123

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Specific heat of the -pyrochlore oxide superconductors CsOs2O6 and RbOs2O6 査読

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

J. Phys. Soc. Jpn.   74 ( 4 )   1255 - 1262   2005年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JPSJ.74.1255

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Photoemission study of YBa2Cu3Oy thin films under light illumination 査読

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

PHYSICAL REVIEW LETTERS   93 ( 24 )   2004年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevLett.93.247006

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Photocarrier injection and the I–V characteristics of La0.8Sr0.2MnO3/SrTiO3:Nb heterojunctions 査読

T Muramatsu, Y Muraoka, Z Hiroi

Solid State Commun.   132 ( 5 )   351 - 354   2004年11月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.ssc.2004.04.051

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

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

85 ( 14 )   2950 - 2952   2004年10月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.1803616

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High pressure effects on superconductivity in the -pyrochlore oxides AOs2O6 (A = K, Rb, Cs) 査読

T Muramatsu, S Yonezawa, Y Muraoka, Z Hiroi

J. Phys. Soc. Jpn.   73 ( 10 )   2912 - 2913   2004年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JPSJ.73.2912

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New -pyrochlore oxide superconductor CsOs2O6 査読

S Yonezawa, Y Muraoka, Z Hiroi

J. Phys. Soc. Jpn.   73 ( 7 )   1655 - 1656   2004年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JPSJ.73.1655

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Unprecedented superconductivity in -pyrochlore osmate KOs2O6 査読

Z Hiroi, S Yonezawa, Y Muraoka

J. Phys. Soc. Jpn.   73 ( 7 )   1651 - 1654   2004年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JPSJ.73.1651

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Photocarrier injection to perovskite manganites 査読

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

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   272   E787 - E788   2004年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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.

DOI： 10.1016/j.jmmm.2003.12.121

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Efficient photocarrier injection to transition metal oxides 査読

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

272   448 - 449   2004年5月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jmmm.2003.12.1290

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New pyrochlore oxide superconductor RbOs2O6 査読

S Yonezawa, Y Muraoka, Y Matsushita, Z Hiroi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 4 )   819 - 821   2004年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.73.819

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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 査読

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年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1103/PhysRevB.69.165104

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Photoemission study of the metal-insulator transition in VO2/TiO2(001): Evidence for strong electron-electron and electron-phonon interaction 査読

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

PHYSICAL REVIEW B   69 ( 16 )   7   2004年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

We have made a detailed temperature-dependent photoemission study of VO2/TiO2(001) thin films, which show a metal-insulator transition at similar to300 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.

DOI： 10.1103/PhysRevB.69.165104

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その他リンク： http://orcid.org/0000-0002-2334-918X

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

S Yonezawa, Y Muraoka, Y Ueda, Z Hiroi

SOLID STATE COMMUNICATIONS   129 ( 4 )   245 - 248   2004年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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.

DOI： 10.1016/j.ssc.2003.10.024

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Superconductivity in a pyrochlore-related oxide KOs2O6 査読

S Yonezawa, Y Muraoka, Y Matsushita, Z Hiroi

JOURNAL OF PHYSICS-CONDENSED MATTER   16 ( 3 )   L9 - L12   2004年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

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.

DOI： 10.1088/0953-8984/16/3/L01

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Photocarrier injection to YBa2CU3O7-x thin films 査読

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

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

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

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

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 12 )   3049 - 3052   2003年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JPSJ.72.3049

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Ultraviolet light selective photodiode based on an organic-inorganic heterostructure 査読

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

APPLIED PHYSICS LETTERS   83 ( 11 )   2097 - 2099   2003年9月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

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&lt;390 nm), and then, it exhibits a large response to the UV-B light (290-320 nm). (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1610793

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Photocarrier injection to transition metal oxides 査読

Y Muraoka, Z Hiroi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 4 )   781 - 784   2003年4月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JPSJ.72.781

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Correlations and semimetallic behaviors in pyrochlore oxide Cd2Re2O7 査読

Z Hiroi, M Hanawa, Y Muraoka, H Harima

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 1 )   21 - 24   2003年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.72.21

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Efficient photocarrier injection in a transition metal oxide heterostructure 査読

Y Muraoka, T Yamauchi, Y Ueda, Z Hiroi

JOURNAL OF PHYSICS-CONDENSED MATTER   14 ( 49 )   L757 - L763   2002年12月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0953-8984/14/49/104

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Second phase transition in pyrochlore oxide Cd2Re2O7 査読

Z Hiroi, JI Yamaura, Y Muraoka, M Hanawa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   71 ( 7 )   1634 - 1636   2002年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.71.1634

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

Y Muraoka, Y Ueda, Z Hiroi

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   63 ( 6-8 )   965 - 967   2002年6月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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Structural phase transition in the superconducting pyrochlore oxide Cd2Re2O7 査読

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

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   63 ( 6-8 )   1027 - 1030   2002年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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 査読

Y Muraoka, Z Hiroi

APPLIED PHYSICS LETTERS   80 ( 4 )   583 - 585   2002年1月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.1446215

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Superconductivity at 1 K in Cd2Re2O7 査読

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

PHYSICAL REVIEW LETTERS   87 ( 18 )   187001   2001年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevLett.87.187001

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

K Ueda, Y Muraoka, H Tabata, T Kawai

APPLIED PHYSICS LETTERS   78 ( 4 )   512 - 514   2001年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

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.

DOI： 10.1063/1.1343844

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

Y Muraoka, H Tabata, T Kawai

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

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/S0038-1098(01)00373-8

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

Y Muraoka, H Tabata, T Kawai

APPLIED PHYSICS LETTERS   77 ( 24 )   4016 - 4018   2000年12月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.1331086

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

Y Muraoka, H Tabata, T Kawai

JOURNAL OF APPLIED PHYSICS   88 ( 12 )   7223 - 7229   2000年12月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.1327601

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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 査読

Y Muraoka, K Ueda, H Tabata, T Kawai

VACUUM   59 ( 2-3 )   622 - 627   2000年11月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/S0042-207X(00)00325-0

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

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年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/jp993096w

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

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

SUPERCONDUCTOR SCIENCE & TECHNOLOGY   13 ( 8 )   1151 - 1154   2000年8月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

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.

DOI： 10.1088/0953-2048/13/8/307

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

Y Muraoka, H Tabata, T Kawai

APPLIED PHYSICS LETTERS   76 ( 9 )   1179 - 1181   2000年2月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.125975

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Preparation of -MnO2 with an open tunnel 査読

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

J. Solid State Chem.   144 ( 1 )   136 - 142   1999年4月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1006/jssc.1999.8133

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Preparation of hexagonal MoO3 by "Chimie Douce" reaction with NO2 査読

Y Muraoka, JC Grenier, S Petit, M Pouchard

SOLID STATE SCIENCES   1 ( 2-3 )   133 - 148   1999年3月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/S1293-2558(00)80070-9

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

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

SOLID STATE IONICS   108 ( 1-4 )   9 - 15   1998年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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 &lt; 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 査読

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年

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Taylor and Francis Inc.  

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 査読

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

JOURNAL OF MATERIALS RESEARCH   12 ( 10 )   2522 - 2525   1997年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：MATERIALS RESEARCH SOCIETY  

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&gt;=0.8) perovskite 査読

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

SOLID STATE COMMUNICATIONS   99 ( 7 )   499 - 502   1996年8月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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 査読

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

PHYSICA C   263 ( 1-4 )   193 - 196   1996年5月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/0921-4534(96)00035-4

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

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

PHYSICA C   263 ( 1-4 )   204 - 207   1996年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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 査読

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

PHYSICA C   233 ( 1-2 )   209 - 213   1994年11月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/0921-4534(94)00591-5

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Synthesis and superconductivity of ‘Hg2Cl2’-intercalated Bi2Sr2Can-1CunOz (n=1-3) compounds 査読

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

Physica C   233 ( 3-4 )   247 - 252   1994年11月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/0921-4534(94)90750-1

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SYNTHESIS AND SUPERCONDUCTIVITY OF OXYCARBONATES OF THE TL-1201 PHASE 査読

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年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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.

DOI： 10.1016/0921-4534(94)90035-3

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

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

PHYSICA C   215 ( 3-4 )   402 - 406   1993年10月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/0921-4534(93)90242-I

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STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF IODINE-INTERCALATED BI2SR2CA1-XYXCU2OZ 査読

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

PHYSICA C   204 ( 1-2 )   65 - 70   1992年12月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/0921-4534(92)90573-U

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