Faculty Profiles - KOBAYASHI, Yoshiaki

Papers - KOBAYASHI, Yoshiaki

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Studies of Multiferroic System of LiCu2O2: II. Magnetic Structures of Two Ordered Phases with Incommensurate Modulations

Kobayashi Yoshiaki, Sato Kenji, Yasui Yukio, Moyoshi Taketo, Sato Masatoshi, Kakurai Kazuhisa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 78 ( 8 ) 2009.8

*Studies on Superconducting LaFe1-yCoyAsO1-xFx (x=0.11) - for the Understanding of the Superconducting Symmetry of Fe-Pnictides - Reviewed

Yoshiaki Kobayashi, Ayaka Kawabata, Sang Chul Lee, Taketo Moyoshi, and Masatoshi Sato

Journal of the Physical Society of Japan Vol. 78 ( 7 ) page： 073704-(1-4) 2009.7

Studies on Superconducting LaFe1-yCoyAsO1-xFx (x=0.11) -For the Understanding of the Superconducting Symmetry of Fe-Pnictides-

Kobayashi Yoshiaki, Kawabata Ayaka, Lee Sang Chul, Moyoshi Taketo, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 78 ( 7 ) 2009.7

Distinct Transport Behaviors of LaFe1-yCoyAsO1-xFx (x=0.11) between the Superconducting and Nonsuperconducting Metallic y Regions Divided by y~0.05 Reviewed

Sang Chul Lee, Ayaka Kawabata, Taketo Moyoshi, Yoshiaki Kobayashi, and Masatoshi Sato

Journal of the Physical Society of Japan Vol. 78 ( 4 ) page： 043703-(1-4) 2009.4

Distinct Transport Behaviors of LaFe1-yCoyAsO1-xFx (x=0.11) between the Superconducting and Nonsuperconducting Metallic y Regions Divided by y similar to 0.05

Lee Sang Chul, Kawabata Ayaka, Moyoshi Taketo, Kobayashi Yoshiaki, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 78 ( 4 ) 2009.4

Studies of the superconductivity of LaFe1-yCoyAsO1-xFx (x=0.11) -impurity effect and NMR Knight shift-

Kawabata Ayaka, Lee Sang Chul, Moyoshi Taketo, Kobayashi Yoshiaki, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 77 page： 147 - 148 2008.11

Studies of the Superconductivity of LaFe1-yCoyAsO1-xFx Reviewed

Ayaka Kawabata, Sang Chul Lee, Taketo Moyoshi, Yoshiaki Kobayashi, and Masatoshi Sato

Journal of the Physical Society of Japan Vol. 77 ( 10 ) page： 103704-(1-4) 2008.10

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

We have prepared the superconducting system LaFe1-yCoyAsO1-xFx (x=0.11) and carried out measurements of their electrical resistivity ρ and superconducting diamagnetism. 75As- and 135La-NMR studies have also been carried out. The Knight shift observed for 75As has been found to be suppressed by the superconductivity; for 135La, the shift is almost insensitive to the superconductivity. This result presents rather strong experimental evidence for singlet pairing. The Co doping effect on the superconducting transition temperature Tc is not so significant as expected for superconductors with nodes, suggesting that the potential scattering does not seem to primarily suppress the superconductivity. Even for superconductors without nodes, it may not be so trivial to expect this small effect, if there are two different (disconnected) Fermi surfaces whose order parameters have opposite signs. As a possible explanation of the observed Tc suppression, which is found to be small, seems to be related with the loss of the itinerant nature of the electrons.

Superconductivity of LaFe1-yCoyAsO1-xFx

Kawabata Ayaka, Lee Sang Chul, Moyoshi Taketo, Kobayashi Yoshiaki, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 77 ( 10 ) 2008.10

Isotope Effect on Superconducting Transition Temperature of NaxCoO2·yH2O Reviewed

Mai Yokoi, Yoshiaki Kobayashi, Masatoshi Sato, and Shunji Sugai

Journal of the Physical Society of Japan Vol. 77 ( 9 ) page： 094713-(1-4) 2008.9

Studies of the Superconductivity of LaFe1-yCoyAsO1-xFx (x=0.11) -Impurity Effect and NMR Knight Shift- Reviewed

Ayaka Kawabata, Sang Chul Lee, Taketo Moyoshi, Yoshiaki Kobayashi, and Masatoshi Sato

Journal of the Physical Society of JapanSupplement C Vol. 77 page： 147-148 2008.9

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

LaFe1-yCoyAsO1-xFx (x=0.11) with various y values were prepared and their electrical resistivities, superconducting diamagnetisms and Hall coefficients have been measured. 75As- and 135La-NMR studies have also been carried out In spite of the successful Co-doping, we have not found any meaningful correlation of Tc with y, which indicates that the Tc-suppression by Co-doping is considered not to be so significant as expected for superconductors with nodes. Even for superconductors without nodes, it may not be easy to expect this small effect on Tc, if there are two different (disconnected) Fermi surfaces whose order parameters have opposite signs. The data of the NMR Knight shift indicate that the Cooper pairs are in the singlet state and the spin susceptibility is almost fully suppressed at low temperature.

Isotope effect on superconducting transition temperature of NaxCoO2 center dot yH(2)O

Yokoi Mai, Kobayashi Yoshiaki, Sato Masatoshi, Sugai Shunji

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 77 ( 9 ) 2008.9

Magnetic Excitations of NaxCoO2·yD2O -Neutron Scattering- Reviewed

Taketo Moyoshi, Yukio Yasui, Yoshiaki Kobayashi, Masatoshi Sato, and Kazuhisa Kakurai

Journal of the Physical Society of Japan Vol. 77 ( 7 ) page： 073709-(1-4) 2008.7

NMR Studies of Successive Phase Transitions in Na0.5CoO2 and K0.5CoO2 Reviewed

Mai Yokoi, Yoshiaki Kobayashi, Taketo Moyoshi, and Masatoshi Sato

Journal of the Physical Society of Japan Vol. 77 ( 7 ) page： 074704-(1-4) 2008.7

Magnetic excitations of NaxCoO2 center dot yD(2)O - Neutron scattering

Moyoshi Taketo, Yasui Yukio, Kobayashi Yoshiaki, Sato Masatoshi, Kakurai Kazuhisa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 77 ( 7 ) 2008.7

NMR studies of successive phase transitions in Na0.5CoO2 and K0.5CoO2

Yokoi Mai, Kobayashi Yoshiaki, Moyoshi Taketo, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 77 ( 7 ) 2008.7

Co-NMR Knight Shift of NaxCoO2·yH2O Studied in Both Superconducting Regions of the Tc-νQ3 Phase Diagram Divided by the Nonsuperconducting Phase Reviewed

Yoshiaki Kobayashi, Taketo Moyoshi, Mai Yokoi, and Masatoshi Sato

Journal of the Physical Society of Japan Vol. 77 ( 6 ) page： 063703-(1-4) 2008.6

Co-NMR knight shift of NaxCoO2 center dot yH(2)O studied in both superconducting regions of the T-c-nu(Q3) phase diagram divided by the nonsuperconducting phase

Kobayashi Yoshiaki, Moyoshi Taketo, Yokoi Mai, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 77 ( 6 ) 2008.6

On the Magnetic Structure of Quasi One Dimensional Spin 1/2 System of Li2ZrCuO4 Reviewed

Yasuko Tarui, Yoshiaki Kobayashi, and Masatoshi Sato

Journal of the Physical Society of Japan Vol. 77 ( 4 ) page： 043703-(1-4) 2008.4

On the magnetic structure of quasi one dimensional spin 1/2 system of Li2ZrCuO4

Tarui Yasuko, Kobayashi Yoshiaki, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 77 ( 4 ) 2008.4

T-3nQ Phase Diagram of Hydrated Cobait Oxides NaxCoO2.yH2O Reviewed

Yoshiaki Kobayashi, Mai Yokoi, Taketo Moyosi and Masatoshi Sato

Journal of the Physical Society of Japan Vol. 76 ( 10 ) page： 103705-(1-5) 2007.10

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

The superconducting transition temperatures Tc of NaxCoO2.yH2O prepared by various methods have been found to exhibit the systematic dependence on the nuclear quadrupole frequency nQ. In the Tc-3nQ Phase Diagram, the superconducting region is divied into two regions by the nonsuperconducting phase. We have investigated the origin of the nonsuperconducting phase by NMR measurements, the results indicate that the nonsuperconducting phase is possibly in the charge disproportionate state.

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Papers - KOBAYASHI, Yoshiaki