研究者詳細 - 村岡　祐治

論文 - 村岡　祐治

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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

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

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

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

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

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

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

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

Retraction: "Unprecedented Superconductivity in

Hiroi Zenji, Yonezawa Shigeki, Muraoka Yuji

J Phys Soc Jpn 74 ( 12 ) 3399 - 3399 2005年12月

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

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

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

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

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

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

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

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

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

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

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

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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