Updated on 2022/04/12

写真a

 
KOBAYASHI, Yoshiaki
 
Organization
Graduate School of Science Associate professor
Graduate School
Graduate School of Science
Undergraduate School
School of Science
Title
Associate professor
Contact information
メールアドレス

Degree 1

  1. Degree of Science ( 1994.3   Gakushuin University ) 

Research Interests 3

  1. strong correlation system

  2. superconductivity

  3. nuclear magnetic resonance

Research Areas 1

  1. Others / Others  / Physical Properties II

Current Research Project and SDGs 5

  1. 鉄系超伝導体の 鉄面内異方性

  2. On the superconducting symmetry of iron pnictide systems

  3. The superconducting state of layered cobalt oxides NaxCoO2.yH2O and the electronic state of the parent compound NaxCoO2

  4. magnetic structure and dielectric property of LiCu2O2 in magnetically ordered phase

  5. The magnetic properties of Cu oxides Li2ZrCuO4 with 1-dimensoinal Cu ribbon

Education 2

  1. Gakushuin University   Graduate School, Division of Science and Technology

    1991.4 - 1994.3

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    Country: Japan

  2. Gakushuin University   Graduate School, Division of Science and Technology

    1989.4 - 1991.3

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    Country: Japan

Professional Memberships 2

  1. The Physical Society of Japan

  2. The Japanese Society for Neutron Science   Affiliate

    2013.11

 

Papers 147

  1. Tailoring a new oxyhydride, CaVO3-xHx, with ordered hydride anions Invited Reviewed

    Yutaka Ueda, Yoshiaki Kobayashi, Masayuki Itoh

    Journal of Solid State Chemistry   Vol. 24   page: 122685   2021.10

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  2. Ultralow-energy magnon anomaly in yttrium iron garnet Reviewed

    Shamoto Shin-ichi, Yasui Yukio, Matsuura Masato, Akatsu Mitsuhiro, Kobayashi Yoshiaki, Nemoto Yuichi, Ieda Jun'ichi

    PHYSICAL REVIEW RESEARCH   Vol. 2 ( 3 )   2020.8

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

    DOI: 10.1103/PhysRevResearch.2.033235

    Web of Science

  3. Successive magnetic transitions and spin structure in the two-leg ladder compound CsFe2Se3 observed by Cs-133 and Se-77 NMR Reviewed

    Murase Mina, Okada Kaoru, Kobayashi Yoshiaki, Hirata Yasuyuki, Hashizume Kazuki, Aoyama Takuya, Ohgushi Kenya, Itoh Masayuki

    PHYSICAL REVIEW B   Vol. 102 ( 1 )   2020.7

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    DOI: 10.1103/PhysRevB.102.014433

    Web of Science

  4. Observation of a Novel Phase Transition in Sr(7)Re(4)O19 Reviewed

    Ueda Yutaka, Murase Mina, Kobayashi Yoshiaki, Itoh Masayuki, Yajima Takeshi, Yamaguchi Tomoki, Takahashi Ryo, Sugimoto Koudai, Ohta Yukinori

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 89 ( 5 )   2020.5

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    DOI: 10.7566/JPSJ.89.054703

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  5. Multipole Fluctuation of Iron Pnictide Superconductor Ba(Fe1−xCox)2As2 Reviewed

    Haruyasu Sato, Mitsuhiro Akatsu, Yuichi Nemoto, Terutaka Goto, Ryosuke Kurihara, Keisuke Mitsumoto, Yoshiaki Kobayashi, and Masatoshi Sato

    JPS Conference Proceedings   Vol. 30   page: 011052-1 - 011052-6   2020

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    DOI: 10.7566/JPSCP.30.011052

  6. Local structure study of the iron-based systems of BaFe2As2 and LiFeAs by X-ray PDF and XAFS analyses

    Li S., Toyoda M., Kobayashi Y., Itoh M., Ikeuchi K., Yoneda Y., Otani A., Matsumura D., Asano S., Mizuki J., Sato M.

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 555   page: 45 - 53   2018.12

  7. In-plane anisotropy of the electric field gradient in Ba(Fe1-xCox)(2)As-2 observed by As-75 NMR

    Toyoda Masayuki, Ichikawa Akihiro, Kobayashi Yoshiaki, Sato Masatoshi, Itoh Masayuki

    PHYSICAL REVIEW B   Vol. 97 ( 17 )   2018.5

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    DOI: 10.1103/PhysRevB.97.174507

    Web of Science

  8. Magnetic excitation and local magnetic susceptibility of the excitonic insulator Ta2NiSe5 investigated by Se-77 NMR

    Li Shang, Kawai Shunsuke, Kobayashi Yoshiaki, Itoh Masayuki

    PHYSICAL REVIEW B   Vol. 97 ( 16 )   2018.4

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    DOI: 10.1103/PhysRevB.97.165127

    Web of Science

  9. Nematic fluctuations in iron arsenides NaFeAs and LiFeAs probed by As-75 NMR

    Toyoda Masayuki, Kobayashi Yoshiaki, Itoh Masayuki

    PHYSICAL REVIEW B   Vol. 97 ( 9 )   2018.3

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    DOI: 10.1103/PhysRevB.97.094515

    Web of Science

  10. Critical Slowing Down of Quadrupole and Hexadecapole Orderings in Iron Pnictide Superconductor

    Kurihara Ryosuke, Mitsumoto Keisuke, Akatsu Mitsuhiro, Nemoto Yuichi, Goto Terutaka, Kobayashi Yoshiaki, Sato Masatoshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 86 ( 6 )   2017.6

  11. Fast recovery of the stripe magnetic order by Mn/Fe substitution in F-doped LaFeAsO superconductors Reviewed

    M. Moroni, P. Carretta, G. Allodi, R. De Renzi, M. N. Gastiasoro, B. M. Andersen, P. Materne, H. H. Klauss, Y. Kobayashi, M. Sato, S. Sanna

    PHYSICAL REVIEW B   Vol. 95 ( 18 ) page: 180501   2017.5

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    DOI: 10.1103/PhysRevB.95.180501

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  12. Metal-insulator transition and magnetic fluctuations in polycrystalline Ru1-xRhxP investigated by 31P NMR Reviewed

    S. Li, Y. Kobayashi, M. Itoh, D. Hirai, and H. Takagi

    PHYSICAL REVIEW B   Vol. 95 ( 15 ) page: 155137   2017.4

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    DOI: 10.1103/PhysRevB.95.155137

    Web of Science

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

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

    PHYSICAL REVIEW B   Vol. 93 ( 23 ) page: 235129   2016.6

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    We have made 53Cr 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
    53Cr 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

  14. X-ray diffraction study of spontaneous strain in the iron-based superconductor Sr4V2Fe2As2O6-delta Reviewed

    M. Saito, H. Fujishita, H. Okamoto, Y. Kobayashi, M. Sato

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 519   page: 142-146   2015.12

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    DOI: 10.1016/j.physc.2015.08.014

  15. Phonons of Fe-based superconductor Ca10Pt4As8(Fe1-xPtxAs)10 Reviewed

    K. keuchi, Y. Kobayashi, K. Suzuki, M. Itoh, R. Kajimoto, P. Bourges, A. D. Christianson, H. Nakamura, M. Machida, M. Sato

    JOURNAL OF PHYSICS-CONDENSED MATTER   Vol. 27 ( 46 ) page: 465701   2015.11

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    DOI: 10.1088/0953-8984/27/46/465701

  16. Enhancement of low-frequency fluctuations and superconductivity breakdown in Mn-doped La1-yYyFeAsO0.89F0.11 superconductors Reviewed

    F. Hammerath, M. Moroni, L. Bossoni, S. Sanna, R. Kappenberger, S. Wurmehl, A. U. B. Wolter, M. A. Afrassa, Y. Kobayashi, M. Sato, B. Buchner, P. Carretta

    PHYSICAL REVIEW B   Vol. 92 ( 2 ) page: 020505   2015.7

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    DOI: 10.1103/PhysRevB.92.020505

  17. Identification of Various Coexisting Phases in Superconducting and Non-superconducting Samples of RbxFe2-ySe2

    Kobayashi Yoshiaki, Kototani Shohei, Ohishi Kazuki, Itoh Masayuki, Hoshikawa Akinori, Ishigaki Toru, Sato Masatoshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 84 ( 4 )   2015.4

  18. Detailed Study of the Phase Diagram of Fe-based Superconductor Ba (Fe1-x Co x) 2As2 by Super High-Resolution Neutron Diffraction Measurements Invited Reviewed

    K Ikeuchi, M Sato, S Li, M Toyoda, Y Kobayashi, M Itoh, P Miao, S Torii, Y Ishikawa, T Kamiyama

    Journal of Physics: Conference Series   Vol. 592 ( 1 ) page: 012071_1 - 012071_5   2015.3

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    DOI: 10.1088/1742-6596/592/1/012071

  19. Identification of Various Coexisting Phases in Superconducting and Non-superconducting Samples of RbxFe2-ySe2 Reviewed

    Yoshiaki Kobayashi, Shohei Kototani, Kazuki Ohishi, Masayuki Itoh, Akinori Hoshikawa, Toru Ishigaki, Masatoshi Sato

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 84 ( 4 ) page: 044710   2015

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  20. Phonons and Spin Excitations in Fe-Based Superconductor Ca10Pt4As8(Fe1-xPtxAs)10 (x~0.2) Reviewed

    K. Ikeuchi, M. Sato, R. Kajimoto, Y. Kobayashi, K. Suzuki, M. Itoh, P. Bourges, A. D. Christianson, H. Nakamura, and M. Machida

    JPS Conf. Proc.   Vol. 3   page: 015043-(1-6)   2014.6

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  21. On the Superconducting Symmetry of Fe-Based Systems -Impurity Effects and Microscopic Magnetic Behavior- Reviewed

    M. Sato, K. Ikeuchi, R. Kajimoto, Y. Kobayashi, Y. Yasui, K. Suzuki, M. Itoh, M. Nakamura, Y. Inamura, M. Arai, P. Bourges, A. D. Christianson, H. Nakamura, and M. Machida

    JPS Conf. Proc.   Vol. 1   page: 014007-(1-12)   2014.3

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  22. Poisoning effect of Mn in LaFe1-xMnxAsO0.89F0.11: Unveiling a quantum critical point in the phase diagram of iron-based superconductors Reviewed

    F. Hammerath, P. Bonfa, S. Sanna, G. Prando, R. D. Renzi, Y. Kobayashi, M. Sato, and P. Carretta

    Phys. Rev. B   Vol. 89   page: 134503   2014.3

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  23. Spin disorder in an Ising honeycomb chain cobaltate

    Igarashi Hirokazu, Shimizu Yasuhiro, Kobayashi Yoshiaki, Itoh Masayuki

    PHYSICAL REVIEW B   Vol. 89 ( 5 )   2014.2

  24. Spin disorder in an Ising honeycomb chain cobaltate Reviewed

    Hirokazu Igarashi, Yasuhiro Shimizu, Yoshiaki Kobayashi, and Masayuki Itoh

    Phys. Rev. B   Vol. 89   page: 054431-(1-5)   2014.2

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  25. 75As NQR and NMR Studies on the Superconducting State of Ca10Pt4As8(Fe1-xPtxAs)10 Reviewed

    Y. Kobayashi, T. Iida, K. Suzuki, T. Kawamata, M. Itoh, and M. Sato

    J. Phys. Soc. Jpn.   Vol. 83 ( 1 ) page: 014712-(1-6)   2013.12

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  26. Phase Separation of Antiferromagnetism and Superconductivity in RbxFe2-ySe2 Observed by using Rb NMR Reviewed

    Y. Kobayashi, S. Saiki, S. Kototani, M. Itoh, and M. Sato

    Journal of the Korean Physical Society   Vol. 63   page: 448-452   2013.9

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  27. In-plane Anisotropy of the Magnetic and the Electric Properties of the Fe Pnictide Ba(Fe1-xCox)2As2

    Y. Kobayashi, A. Ichikawa, M. Toyoda, M. Itoh, and M. Sato

    Journal of the Korean Physical Society   Vol. 63   page: 481-485   2013.9

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  28. Magnetism and superconductivity in Rb (x) Fe2-y Se-2

    Ohishi Kazuki, Sato Masatoshi, Kototani Shouhei, Saiki Shunsuke, Kobayashi Yoshiaki, Itoh Masayuki

    JOURNAL OF THE KOREAN PHYSICAL SOCIETY   Vol. 62 ( 12 ) page: 1994 - 1996   2013.7

  29. Onset of magnetism in optimally electron-doped LFe1-xRuxAsO1-yFy (L = La, Nd, or Sm) superconductors around x=1/4,

    S. Sanna, P. Carretta, R. De Renzi, G. Prando, P. Bonfà, M. Mazzani, G. Lamura, T. Shiroka, Y. Kobayashi, and M. Sato

    Phys. Rev. B   Vol. 87   page: 134518-(1-6)   2013

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  30. On the superconducting symmetry of Fe-based systems - Impurity effect studies and neutron scattering measurements Reviewed

    Masatoshi Sato, Yoshiaki Kobayashi, Takayuki Kawamata, Yukio Yasui, Kazunori Suzuki, Masayuki Itoh,. Ryoichi Kajimoto, Kazuhiko Ikeuchi, Masatoshi Arai, Phillipe Bourges

    Journal of the Korean Physical Society   Vol. 62 ( 12 ) page: 1726-1733   2013

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  31. Magnetism and superconductivity in RbxFe2-ySe2 Reviewed

    Kazuki Ohishi, Masatoshi Sato, Shouhei Kototani, Shunsuke Saiki, Yoshiaki Kobayashi, Masayuki Itoh

    Journal of the Korean Physical Society   Vol. 62 ( 12 ) page: 1994-1996   2013

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  32. On the superconducting pairing mechanism of Fe-based systems-Is it new or well-known? Reviewed

    M. Sato and Y. Kobayashi

    Solid State Communications   Vol. 152 ( 8 ) page: 688–694   2012.8

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  33. X-ray diffraction study of spontaneous strain in Fe-pnictide superconductor, NdFeAsO0.89F0.11 Reviewed

    H. Fujishita, Y. Hayashi, M. Saito, H. Unno, H. Kaneko, H. Okamoto, M. Ohashi, Y. Kobayashi, M. Sato

    European Physical Journal B   Vol. 85 ( 2 ) page: 52   2012.2

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  34. NMR Studies on Iron Pnictide Superconductors of LaFeAsO0.89F0.11 and Ca-Fe-Pt-As Reviewed

    Y. Kobayashi, T. Iida, K. Suzuki, E. Satomi, T. Kawamata, M. Itoh, and M. Sato

    Journal of Physics: Conference Series   Vol. 400   page: 022056   2012

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  35. Impurity effects on the superconducting transition temperatures of Fe pnictides and superconducting symmetry of the order parameter Reviewed

    M. Sato, Y. Kobayashi, S. Satomi, T. Kawamata and M. Itoh

    Journal of Physics: Conference Series   Vol. 400   page: 022104   2012

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  36. Study of magnetic excitation spectra of several Fe-pnictide systems Reviewed

    M Sato, T Kawamata, Y Kobayashi, Y Yasui, T Iida, K Suzuki, M Itoh, T Moyoshi, K Motoya, R Kajimoto, M Nakamura, Y Inamura and M Arai

    Journal of Physics: Conference Series   Vol. 400   page: 022105   2012

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  37. Absence of Magnetic Order in Ising Honeycomb-Lattice Ba3Co2O6(CO3)(0.7)

    Igarashi Kazuhiro, Shimizu Yasuhiro, Satomi Erika, Kobayashi Yoshiaki, Takami Tsuyoshi, Itoh Masayuki

    26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5   Vol. 400   2012

  38. NMR Studies on Iron Pnictide Superconductors of LaFeAsO0.89F0.11 and Ca-Fe-Pt-As

    Kobayashi Y., Iida T., Suzuki K., Satomi E., Kawamata T., Itoh M., Sato M.

    26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5   Vol. 400   2012

  39. Magnetic Excitation Spectra of Superconducting Ca-Fe-Pt-As System Reviewed

    M. Sato, T. Kawamata, Y. Kobayashi, Y. Yasui, Takefumi Iida, Kazunori Suzuki, Masayuki Itoh, Taketo Moyoshi, Kiyoichiro Motoya, Ryoichi Kajimoto, Mitsutaka Nakamura, Yasuhiro Inamura, and Masatoshi Arai

    Journal of the Physical Society of Japan   Vol. 80   page: 093709-(1-4)   2011

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  40. Crystal Structure of New Pt-Doped Fe Pnictide Superconductors Reviewed

      Vol. 80   page: 073710-(1-3)   2011

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  41. Study of Ni-Doping Effect of Specific Heat and Transport Properties for LaFe1-yNiyAsO0.89F0.11 Reviewed

    T. Kawamata, E. Satomi, Y. Kobayashi, M. Itoh, and M. Sato

    Journal of the Physical Society of Japan   Vol. 80   page: 084720-(1-5)   2011

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  42. Magnetic Ordering in V-Layers of the Superconducting System of Sr2VFeAsO3 Reviewed

    S. Tatematsu, E. Satomi, Y. Kobayashi, and M. Sato

    J. Phys. Soc. Jpn.   Vol. 79 ( 12 ) page: 123712-(1-4)   2010.12

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  43. Distinct physical behaviors of LaFe1-yCoyAsO0.89F0.11 between the superconducting and nonsuperconducting metallic regions of y divided by y similar to 0.05

    Sato M., Kobayashi Y., Lee S. C., Takahashi H., Moyoshi T.

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 470   page: S475 - S477   2010.12

  44. Studies on the superconducting state of NaxCoO2 center dot yH(2)O - Overview

    Sato Masatoshi, Kobayashi Yoshiaki, Moyoshi Taketo

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 470   page: S673 - S677   2010.12

  45. On the non-superconducting state in the phase diagram of NaxCoO2 center dot yH(2)O

    Sato Masatoshi, Kobayashi Yoshiaki, Moyoshi Taketo

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 470   page: S752 - S754   2010.12

  46. NMR studies on the superconducting symmetry of iron pnictide systems

    Kobayashi Yoshiaki, Lee Sang Chul, Takahashi Hidefumi, Moyoshi Taketo, Sato Masatoshi

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 470   page: S472 - S474   2010.12

  47. Magnetic excitations of superconducting LaFeAsO0.89F0.11

    Moyoshi T., Lee S. C., Tatematsu S., Yasui Y., Kobayashi Y., Sato M., Kakurai K.

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 470   page: S470 - S471   2010.12

  48. 75As-NMR Studies of LaFeAsO1-xFx for Various x Values Reviewed

    Yoshiaki Kobayashi, Erika Satomi, Sang Chul Lee, and Masatoshi Sato

    Journal of the Physical Society of Japan   Vol. 79 ( 9 ) page: 093709-(1-4)   2010.9

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    Results of 75As NMR and NQR measurements are reported for superconducting samples of LaFeAsO1-xFRx with various x values. The x dependent widths of the superconducting transition and those of the NQR spectra indicate that the optimally doped LaFeAsO1-xFx sample with the superconducting transition temperature Tc=28 K has the smallest width or smallest inhomogeneity of the superconducting order parameter Δ. In the analyses of the temperature (T) dependence of the NMR longitudinal relaxation rate 1/T1, we have tried to use a simple relation 1/T1~Tn to see how fast 1/T1 decreases when the superconducting order parameter grows. The relation holds rather well in the T region of ~0.3Tc<T=<Tc, and n varies from 2.5-6 with varying x, having the maximum value 5-6 at the optimal x. These results indicate that the x dependence of n originates from the spatial distribution of Δ, and that the T5-6 behavior is considered to be intrinsic to this system.

    DOI: 10.1143/JPSJ.79.093709

  49. Superconducting Transition Temperatures and Transport Properties of LaFe1-yRuyAsO0.89F0.11 and LaFeAsO0.89-xF0.11+x Reviewed

    Erika Satomi, Sang Chul Lee, Yoshiaki Kobayashi, and Masatoshi Sato

    Journal of the Physical Society of Japan   Vol. 79 ( 9 ) page: 094702 (6 pages)   2010.9

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    The transport behaviors and superconducting transition temperatures Tc of the title systems have been experimentally studied for various x and y values. Together with results reported previously by our group, data are now available for many sets of samples of RFe1-yMyAsO0.89F0.11 with R = La and Nd and M = Co, Mn and Ru and for RFeAsO0.89-xF0.11+x. Dopings of Co and Mn atoms introduce electrons and holes into the FeAs planes, respectively. They also introduce, more or less, randomness effects. Ru atoms introduce scattering centers within the FeAs planes without changing the number of carrier electrons or holes. In contrast, F atoms introduce electron carriers, but not randomness effects or scattering centers into the FeAs planes. From these studies, we can conclude that there are two appreciable mechanisms of Tc suppression by the dopings. The disappearance of or reduction in the area of the hole Fermi surfaces around the Γ point in the reciprocal space has been clearly shown as one of the mechanisms, irrespective of whether or not doped atoms are within the conducting planes. The other mechanism is the electron localization observed for the Mn doping. The rates of the Tc suppression due to the scattering by nonmagnetic Ru and Co atoms have been found to be negligible compared with that expected from the pair breaking theory, indicating that the systems do not have the S± symmetry of the superconducting order parameter.

    DOI: 10.1143/JPSJ.79.094702

    Web of Science

  50. High-Temperature Multiferroic State of RBaCuFeO5 (R = Y, Lu, and Tm)

    Kawamura Yuji, Kai Takahiro, Satomi Erika, Yasui Yukio, Kobayashi Yoshiaki, Sato Masatoshi, Kakurai Kazuhisa

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 79 ( 7 )   2010.7

  51. Superconducting transition temperature and the thickness of CoO2 planes of NaxCoO2 center dot yH(2)O

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

    SOLID STATE SCIENCES   Vol. 12 ( 5 ) page: 656 - 659   2010.5

  52. Effects of Ru Doping on the Transport Behavior and Superconducting Transition Temperature of NdFeAsO0.89F0.11 Reviewed

    Sang Chul Lee, Erika Satomi, Yoshiaki Kobayashi, and Masatoshi Sato

    Journal of the Physical Society of Japan   Vol. 79 ( 2 ) page: 023702-(1-4)   2010.2

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    The transport behavior and superconducting transition temperature Tc of NdFe1-yRuyAsO0.89F0.11 have been studied for various y values. Because Ru impurities are isoelectronic to host Fe atoms, we basically expect that the number of electrons does not change with y, at least in the region of small y values. The results indicate that the rate of Tc suppression by Ru atoms is too small to be explained by the pair breaking effect of nonmagnetic impurities expected for the S± symmetry, confirming our previous results for Co doping.

    DOI: 10.1143/JPSJ.79.023702

    Web of Science

  53. Studies on Effects of Impurity Doping and NMR Measurements of La 1111 and/or Nd 1111 Fe-Pnictide Superconductors Reviewed

    Masatoshi Sato, Yoshiaki Kobayashi, Sang Chul Lee, Hidefumi Takahashi, Erika Satomi, and Yoko Miura

    Journal of the Physical Society of Japan   Vol. 79 ( 1 ) page: 014710-(1-10)   2010.1

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    DOI: 10.1143/JPSJ.79.014710

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  54. NMR studies on the superconducting symmetry of iron pnictide systems Reviewed

    Y. Kobayashi, S.C. Lee, H. Takahashi, T. Moyoshi, M. Sato

    Physica C: Superconductivity   Vol. 470   page: S472-S474   2010

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  55. Studies on Effects of Impurity Doping and NMR Measurements of La 1111 and/or Nd 1111 Fe-Pnictide Superconductors Reviewed

    Masatoshi Sato, Yoshiaki Kobayashi, Sang Chul Lee, Hidefumi Takahashi, Erika Satomi, and Yoko Miura

    Journal of the Physical Society of Japan   Vol. 79 ( 1 ) page: 014710   2009.12

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    Measurements of the electrical resistivity rho, Hall coefficient RH, thermoelectric power S, and the electronic specific heat coefficient gamma have been carried out for samples of LnFe1-yMyAsO1-xFx (Ln=La, Nd; M=Co, Mn; x=0.11) obtained by doping M atoms into the superconducting LnFeAsO1-xFx (Ln 1111) system. The NMR longitudinal relaxation rate 1/T1 has also been measured for samples of LaFe1-yCoyAsO1-xFx with various x values. Co atoms doped into the superconducting LnFeAsO1-xFx are nonmagnetic, and the rate of Tc-suppression absolute value of dTc/dx by Co atoms has been found to be too small to be explained by the pair-breaking effect expected for the S+- superconducting symmetry proposed as the most probable symmetry for the system. This result throws a serious doubt on whether the symmetry is realized in the system. Instead of the pair breaking, two mechanisms of Tc suppression by the doped impurities have been found: One is the electron localization, which appears when the sheet resistance r/sheet exceeds h/4e2=6.45 k-ohme, and the other is the disappearance (or reduction in the area) of the hole Fermi surfaces around the Gamma point in the reciprocal space. The latter mechanism has been observed when the number of electrons increases with increasing Co doping level and the system changes from an anomalous metal to an ordinary one. Regarding the two distinct T dependences of the NMR longitudinal relaxation rate 1/T1 of LaFeAsO1-xFx, we discuss the origin of such a difference, and show that, at least, the T2.5-3.0-like dependence of 1/T1 cannot be considered as the experimental evidence for the S+- symmetry of Delta.

    DOI: 10.1143/JPSJ.79.014719/

  56. Studies of Multiferroic System LiCu2O2: I. Sample Characterization and Relationship between Magnetic Properties and Multiferroic Nature Reviewed

    Yukio Yasui, Kenji Sato, Yoshiaki Kobayashi, and Masatoshi Sato

    J. Phys. Soc. Jpn.   Vol. 78 ( 8 ) page: 084720-(1-5)   2009.8

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

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

    Journal of the Physical Society of Japan   Vol. 78 ( 8 ) page: 084721-(1-5)   2009.8

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    Neutron diffraction and 7Li-NMR have been applied to determine the three dimensional magnetic structures of the multiferroic system LiCu2O2, which has four chains (ribbon chains) of edge-sharing CuO4 square planes in a unit cell. First, we have confirmed that there are successive magnetic transitions at TN1 = 24.5 K and TN2 = 22.8 K. In the T region between TN1 and TN2, the quasi one-dimensional spins (S = 1/2) of Cu2+ ions within a chain have a collinear and sinusoidally modulated structure with Cu-moments parallel to the c-axis and with the modulation vector along the b-axis. At T < TN2, an ellipsoidal helical spin structure with the incommensurate modulation has been found. We present detailed parameters, describing the modulation amplitudes, helical axis vectors as well as the relative phases of the modulations of four ribbon chains, which can well reproduce both the NMR and neutron results, in the two magnetically ordered phases. This finding of the rather precise magnetic structures enables us to discuss the relationship between the magnetic structure and the multiferroic nature of the present system in zero magnetic field, as presented in our companion paper (paper I), and open a way how to understand the reported electric polarization under the finite magnetic field.

  58. Studies of Multiferroic System LiCu2O2: I. Sample Characterization and Relationship between Magnetic Properties and Multiferroic Nature

    Yasui Yukio, Sato Kenji, Kobayashi Yoshiaki, Sato Masatoshi

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

  59. 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

  60. *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

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  61. 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

  62. 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

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  63. 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

  64. 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

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  65. 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

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    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.

  66. 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

  67. Isotope Effect on Superconducting Transition Temperature of NaxCoO2&middot;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

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  68. 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

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    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.

  69. 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

  70. Magnetic Excitations of NaxCoO2&middot;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

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  71. 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

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  72. 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

  73. 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

  74. Co-NMR Knight Shift of NaxCoO2&middot;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

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  75. 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

  76. 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

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  77. 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

  78. 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

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    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.

  79. T-3v(Q) phase diagram of hydrated cobalt oxides Na(x)CoO(2 center dot)yH(2)O

    Kobayashi Yoshiaki, Yokoi Mai, Moyoshi Taketo, Sato Masatoshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 76 ( 10 )   2007.10

  80. Magnetic Behavior of Spin-1/2 Frustrated System Hg2Cu2F6S Reviewed

    Shohei Kawabata, Yukio Yasui, Yoshiaki Kobayashi and Masatoshi Sato

    Journal of the Physical Society of Japan   Vol. 76 ( 8 ) page: 084705-(1-5)   2007.8

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  81. Magnetic Behavior of spin-1/2 frustrated system Hg2Cu2F6S

    Kawabata Shohei, Yasui Yukio, Kobayashi Yoshiaki, Sato Masatoshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 76 ( 8 )   2007.8

  82. Magnetic and thermal properties of Co3V2O8 and Ni3V2O8

    Kobayashi Yusuke, Yasui Yukio, Sato Masatoshi

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: 1160 - 1161   2007.3

  83. Studies of successive transitions in K0.5CoO2

    Yokoi Mai, Mori Yoshihiko, Moyoshi Taketo, Kobayashi Yoshiaki, Sato Masatoshi

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: 672 - 674   2007.3

  84. Spin-gap behavior of distorted honeycomb lattice system Na3Cu2SbO6

    Miura Yoko, Hirai Riu, Fujita Toshiaki, Kobayashi Yoshiaki, Sato Masatoshi

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: E389 - E391   2007.3

  85. NMR studies of successive transition in Na0.5CoO2

    Kobayashi Y., Yokoi M., Moyoshi T., Watanabe H., Sato M.

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: 675 - 677   2007.3

  86. NMR and neutron scattering studies on NaxCoO2 center dot yH(2)O

    Sato M., Kobayashi Y., Moyoshi T., Yokoi M., Watanabe H., Mori Y., Kakurai K.

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: 666 - 668   2007.3

  87. Ferroelectric transition induced by the incommensurate magnetic ordering in LiCuVO4

    Naito Yutaka, Sato Kenji, Yasui Yukio, Kobayashi Yusuke, Kobayashi Yoshiaki, Sato Masatoshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 76 ( 2 )   2007.2

  88. Structural studies of pyrochlore-related spin-1/2 system Ag2Cu2O3

    Uematsu Daisuke, Soda Minoru, Kobayashi Yoshiaki, Sato Masatoshi, Igawa Naoki, Kakurai Kazuhisa

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 12 )   2006.12

  89. Existence of Co3+ low-spin state in TbBaCo2O5.5

    Soda Minoru, Yasui Yukio, Kobayashi Yoshiaki, Fujita Toshiaki, sato Mashi Sato, Kakurai Kazuhisa

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 10 )   2006.10

  90. Spin-Gap Behavior of Na3Cu2SbO6 with Distorted Honeycomb Structure Reviewed

    Yoko Miura, Riu Hirai, Yoshiaki Kobayashi and Masatoshi Sato

    Journal of the Physical Society of Japan   Vol. 75 ( 8 ) page: 084707-(1-6)   2006.8

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  91. Spin-gap behavior of Na3Cu2SbO6 with distorted honeycomb structure

    Miura Yoko, Hirai Riu, Kobayashi Yoshiaki, Sato Masatoshi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 8 )   2006.8

  92. Magnetic properties of Superconducitng Cobait Oxides NaxCoO2.yH2O Reviewed

    Yoshiaki Kobayshi, taketo Moyoshi, Hidekazu Watanabe Mai Yokoi and Masatoshi Sato

    Journal of the Physical Society of Japan   Vol. 75 ( 7 ) page: 074717-(1-6)   2006.7

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  93. Search for Magnetic Excitation Spectra of NaxCoO2.yD2O -Neutron Scattering- Reviewed

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

    Journal of the Physical Society of Japan   Vol. 75 ( 7 ) page: 074705-(1-6)   2006.7

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  94. Magnetic properties of superconducting cobalt oxides NaxCoO2 center dot yH(2)O

    Kobayashi Yoshiaki, Moyoshi Taketo, Watanabe Hidekazu, Yokoi Mai, sato Mashi Sato

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 7 )   2006.7

  95. Search for magnetic excitation spectra of NaxCoO2 center dot yD(2)O - Neutron scattering

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

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 7 )   2006.7

  96. Magnetic and metal-insulator transitions in beta-Na0.5CoO2 and gamma-K0.5CoO2 - NMR and neutron diffraction studies

    Watanabe H, Mori Y, Yokoi M, Moyoshi T, Soda M, Yasui Y, Kobayashi Y, Sato M, Igawa N, Kakurai K

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 75 ( 3 )   2006.3

  97. *Magnetic correlation of NaxCoO2 and Successive Phase Transitions of Na0.5CoO2 -NMR and Neutron Diffraction Studies- Reviewed

    Mai Yokoi, Taketo Moyoshi, Yoshiaki Kobayashi, Munoru Soda, Yukio Yasui, Masatoshi Sato and Kazushi Kakurai

    Journal of the Physical Society of Japan   Vol. 74 ( 11 ) page: 3046-3056   2005.11

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  98. Co-59-NMR Knight shift of superconducting three-layer NaxCoO2 center dot yH(2)O

    Watanabe H, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 74 ( 9 ) page: 2563 - 2567   2005.9

  99. 59Co-NMR Knight shift of Aligned Crystal and Polycrystalline Samples of Superconducting Na0.3CoO2.1.3H2O Reviewed

    Yoshiaki Kobayashi, Hidekazu Watanabe, Mai Yokoi, Taketo Moyoshi, Yoshihiko Mori and Masatoshi Sato

    Journal of the Physical Society of Japan   Vol. 74 ( 6 ) page: 1800-1805   2005.6

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  100. Co-59-NMR knight shift of aligned crystals and polycrystalline samples of superconducting Na0.3CoO2 center dot 1.3H(2)O

    Kobayashi Y, Watanabe H, Yokoi M, Moyoshi T, Mori Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 74 ( 6 ) page: 1800 - 1805   2005.6

  101. ESR studies on quasi one-dimensional spin system TiOBr

    Kato C, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 74 ( 1 ) page: 473 - 477   2005.1

  102. Impurity effects on the superconducting transition temperature of NazCoO2 center dot yH(2)O

    Yokoi M, Watanabe H, Mori Y, Moyoshi T, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 73 ( 5 ) page: 1297 - 1302   2004.5

  103. Magnetic structure of a spinel system Cu0.3Zn0.7Cr2Se4

    Iikubo S, Yasui Y, Kobayashi Y, Ohno Y, Ito M, Soda M, Sato M, Kakurai K

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 272   page: 473 - 474   2004.5

  104. Ru-NMR studies and specific heat measurements of Bi3Ru3O11 and La4Ru6O19

    Tsuchida K, Kato C, Fujita T, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 73 ( 3 ) page: 698 - 702   2004.3

  105. Co-59-NMR knight shift of superconducting NaxCoO2 center dot yH(2)O

    Kobayashi Y, Yokoi M, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 72 ( 10 ) page: 2453 - 2455   2003.10

  106. Co-59 NQR study on superconducting NaxCoO2 center dot yH(2)O

    Kobayashi Y, Yokoi M, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 72 ( 9 ) page: 2161 - 2164   2003.9

  107. NMR studies of Co-oxides with large thermoelectric performance

    Kobayashi Y, Masuda H, Miyashita T, Sato M, Itoh M, Terasaki I

    PHYSICA B-CONDENSED MATTER   Vol. 329   page: 926 - 927   2003.5

  108. Spin-state change of co atoms of La4Co3O10+delta

    Miyashita T, Kobayashi Y, Fukamachi T, Masuda H, Sato M

    PHYSICA B-CONDENSED MATTER   Vol. 329   page: 740 - 742   2003.5

  109. Spin-glass-like transition and Hall resistivity of Y2-xBixIr2O7

    Aito N, Soda M, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 72 ( 5 ) page: 1226 - 1230   2003.5

  110. Transport, thermal and magnetic properties of Bi3Os3O11 and Bi3Ru3O11

    Fujita T, Tsuchida K, Yasui Y, Kobayashi Y, Sato M

    PHYSICA B-CONDENSED MATTER   Vol. 329   page: 743 - 744   2003.5

  111. Transport, thermal and magnetic properties of pyrochlore oxides Y2-xBixIr2O7

    Soda M, Aito N, Kurahashi Y, Kobayashi Y, Sato M

    PHYSICA B-CONDENSED MATTER   Vol. 329   page: 1071 - 1073   2003.5

  112. Transport and magnetic properties of R(1-x)A(x)CoO(3) (R = La, Pr and Nd; A = Ba, Sr and Ca)

    Masuda H, Fujita T, Miyashita T, Soda M, Yasui Y, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 72 ( 4 ) page: 873 - 878   2003.4

  113. *59Co-NMR Knight Shift of Superconducting NaxCoO2&middot;yH2O Reviewed

    Yoshiaki Kobayashi, Mai Yokoi and Masatoshi Sato

    Journal of the Physical Society of Japan   Vol. 72   page: 2453-2455   2003

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    Layered Co oxide NaxCoO2&middot;yH2O with the superconducting transition temperature Tc=4.5 K has been studied by 59Co-NMR. The Knight shift K estimated from the observed spectra of a powder sample exhibits almost temperature (T)-independent behavior above Tc and decreases with decreasing T below Tc. This result and the existence of the coherence peak in the spin–lattice relaxation rate versus T curve reported by the present authors indicate, naively speaking, that the singlet order parameter with s-wave symmetry is realized in NaxCoO2&middot;yH2O. Differences in the observed behaviors between the spectra of a nonaligned sample and those of an aligned sample embedded in epoxy adhesive by applying an external magnetic field are discussed.

  114. Co-59-NMR studies on La4Co3O10+delta

    Miyashita T, Kobayashi Y, Fukamachi T, Masuda H, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 71 ( 12 ) page: 3043 - 3046   2002.12

  115. Magnetic structure and the Hall resistivity of Cu1-xZnxCr2Se4

    Iikubo S, Yasui Y, Oda K, Ohno Y, Kobayashi Y, Sato M, Kakurai K

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 71 ( 11 ) page: 2792 - 2799   2002.11

  116. Transport and NQR studies of Nd1.6-xCexSr0.4CuO4 with T* structure

    Ambai M, Kobayashi Y, Iikubo S, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 71 ( 2 ) page: 538 - 542   2002.2

  117. Unusual anomalous Hall resistivities of CuCr2S4, Cu0.5Zn0.5Cr2Se4 and Cr3Te4

    Oda K, Yoshii S, Yasui Y, Ito M, Ido T, Ohno Y, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 70 ( 10 ) page: 2999 - 3005   2001.10

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  118. Studies on successive electronic state changes in systems with NiO2 planes-La-139-NMR/NQR-

    Fukamachi T, Oda K, Kobayashi Y, Miyashita T, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 70 ( 9 ) page: 2757 - 2764   2001.9

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  119. Cu NQR study on the "wipeout" phenomenon in YBa2Cu3Oy

    Kobayashi Y, Miyashita T, Ambai M, Fukamachi T, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 70 ( 4 ) page: 1133 - 1136   2001.4

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  120. La-139 NMR studies of layered perovskite systems La3Ni2O7-delta and La4Ni3O10

    Fukamachi T, Kobayashi Y, Miyashita T, Sato M

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   Vol. 62 ( 1-2 ) page: 195 - 198   2001

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  121. NMR studies of Ga in magnetically frustrated pyrochlore system R2GaSbO7 (R = rare earth elements)

    Kobayashi Y, Miyashita T, Fukamachi T, Sato M

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   Vol. 62 ( 1-2 ) page: 347 - 350   2001

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  122. Absence of the "wipeout" phenomenon in the NQR spectra of YBa2Cu3O6.61

    Kobayashi Y, Miyashita T, Ambai M, Fukamachi T, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 69 ( 8 ) page: 2435 - 2438   2000.8

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  123. On the anomalous oxygen-number dependence of the superconducting transition temperature of R1-xPrxBa2Cu3O6+y (R=Y and Sm)

    Ambai M, Yasui Y, Takeda J, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 69 ( 1 ) page: 170 - 177   2000.1

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  124. Magnetization measurements and Rb-87-NMR on Rb2M3S4 (M=Ni and Pd) with the Kagome lattice

    Fukamachi T, Kobayashi Y, Nakamura A, Harashina H, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 68 ( 11 ) page: 3668 - 3672   1999.11

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  125. Effects of short range spin correlation on ESR lines of low-dimensional antiferromagnetic and spin-gapped systems

    Taniguchi S, Kato M, Kodama K, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 68 ( 6 ) page: 2118 - 2127   1999.6

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  126. Thermal conductivity of BaCo1-xNixS2

    Takeda J, Sakurai J, Nakamura A, Kato M, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 68 ( 5 ) page: 1602 - 1606   1999.5

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  127. On the magnetic properties of systems with low dimensional linkage of VO5 pyramids

    Kanada M, Harashina H, Tanaka S, Fukamachi T, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 67 ( 8 ) page: 2904 - 2909   1998.8

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  128. NMR studies on spin-gap behavior of monoclinic CuNb2O6

    Fukamachi T, Kobayashi Y, Kanada M, Kasai M, Yasui Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 67 ( 6 ) page: 2107 - 2111   1998.6

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  129. Spin-gap behavior of CuNb2O6

    Kodama K, Fukamachi T, Harashina H, Kanada M, Kobayashi Y, Kasai M, Sasaki H, Sato M, Kakurai K

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 67 ( 1 ) page: 57 - 60   1998.1

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  130. V-51-NMR study of the misfit layer compounds La1.17-xSrxVS3.17

    Kobayashi Y, Kasai M, Yasui Y, Nishikawa T, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 66 ( 12 ) page: 4027 - 4030   1997.12

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  131. ESR studies on CaV4O9 and CaV3O7

    Taniguchi S, Kobayashi Y, Kasai M, Kodama K, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 66 ( 11 ) page: 3660 - 3664   1997.11

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  132. Electron- and photon-thermal conductivity of high-T-c systems from the underdoped insulating to the nonsuperconducting metallic phase

    Kamijo H, Takeda J, Hayashi F, Ueda E, Fujiwara K, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 66 ( 8 ) page: 2466 - 2472   1997.8

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  133. Structural studies on the phase transition of La3Ni2O6.92 at about 550 K

    Sasaki H, Harashina H, Taniguchi S, Kasai M, Kobayashi Y, Sato M, Kobayashi T, Ikeda T, Takata M, Sakata M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 66 ( 6 ) page: 1693 - 1697   1997.6

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  134. Study of spin-gap formation in quasi-two-dimensional S=1/2 system CaV4O9: Neutron scattering and NMR

    Kodama K, Harashina H, Sasaki H, Kobayashi Y, Kasai M, Taniguchi S, Yasui Y, Sato M, Kakurai K, Mori T, Nishi M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 66 ( 3 ) page: 793 - 802   1997.3

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  135. Transport and magnetic properties of La3Ni2O7-delta and La4Ni3O10-delta

    Kobayashi Y, Taniguchi S, Kasai M, Sato M, Nishioka T, Kontani M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 65 ( 12 ) page: 3978 - 3982   1996.12

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  136. Strong pressure effect on the electrical resistivity of BaCo1-xNixS2

    Yasui Y, Kobayashi Y, Takeda J, Shamoto S, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 65 ( 9 ) page: 2757 - 2760   1996.9

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  137. Thermal properties of two dimensional Mott system La-1.17-xSrxVS3.17

    Nishikawa T, Yasui Y, Kobayashi Y, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 65 ( 8 ) page: 2543 - 2547   1996.8

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  138. Electron and magnon contributions to the thermal conductivity of YBa2Cu3Oy (6.1<=y<=6.9) at low temperatures

    Kamijo H, Kobayashi Y, Ueda E, Sato M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 65 ( 6 ) page: 1551 - 1554   1996.6

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  139. Studies of the metal-insulator transition of misfit-layer compounds La1.17-xSrVS3.17

    Nishikawa T, Yasui Y, Kobayashi Y, Sato M

    PHYSICA C   Vol. 263 ( 1-4 ) page: 554 - 557   1996.5

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  140. EFFECTS OF CARRIER DOPING INTO THE MISFIT-LAYER COMPOUNDS (LA(1-Y)R(Y)S)(1+ALPHA)VS2 (R=SR AND PB) - TRANSPORT AND MAGNETIC STUDIES

    YASUI Y, NISHIKAWA T, KOBAYASHI Y, SATO M, NISHIOKA T, KONTANI M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 64 ( 10 ) page: 3890 - 3896   1995.10

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  141. SPIN GAP BEHAVIOR OF S=1/2 QUASI-2-DIMENSIONAL SYSTEM CAV4O9

    TANIGUCHI S, NISHIKAWA T, YASUI Y, KOBAYASHI Y, SATO M, NISHIOKA T, KONTANI M, SANO K

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 64 ( 8 ) page: 2758 - 2761   1995.8

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  142. TRANSPORT, MAGNETIC AND THERMAL-PROPERTIES OF BACO1-XNIXS2

    TAKEDA J, KOBAYASHI Y, KODAMA K, HARASHINA H, SATO M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 64 ( 7 ) page: 2550 - 2557   1995.7

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  143. TRANSPORT, MAGNETIC AND THERMAL-PROPERTIES OF LA3NI2O7-DELTA

    TANIGUCHI S, NISHIKAWA T, YASUI Y, KOBAYASHI Y, TAKEDA J, SHAMOTO S, SATO M

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 64 ( 5 ) page: 1644 - 1650   1995.5

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  144. 1H-NMR investigation of the SDW wave-number in (TMTTF)2Br Reviewed

    T. Nakamura, T. Nobutoki, Y. Kobayashi, T. Takahashi, G. Saito

    Synthetic Metals(Elsevier)   Vol. 70 ( 1-3 ) page: 1293 - 1294   1995.3

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  145. Magnetic properties of the insulating state of the organic superconductor, β-[(CH3)4N][Pd(dmit)2]2 Reviewed

    Synthetic Metals (Elsevier)   Vol. 70 ( 1-3 ) page: 1043 - 1044   1995.3

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    DOI: 10.1016/0379-6779(94)02749-O

  146. Observation of the coherence peak of 1H-NMR relaxation rate in the superconducting state of (MDT-TTF)2Aul2 Reviewed

    Y. Kobayashi, T. Nakamura, T. Takahashi, K. Kanoda, B. Hilti, J. S. Zambounis

    Synthetic Metals(Elsevier)   Vol. 70 ( 1-3 ) page: 871 - 872   1995.3

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    DOI: 10.1016/0379-6779(94)02684-Q

  147. Symmetry of the order parameter in organic superconductors:(MDT-TTF) 2Aul2 vs.(TMTSF) 2ClO4 Invited Reviewed

    T Takahashi, Y Kobayashi, T Nakamura, K Kamoda, B Hilti, JS Zambounis

    Physica C: Superconductivity (North-Holland)   Vol. 7 ( 3 ) page: 636 - 666   1994.12

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    DOI: 10.1016/0921-4534(94)92451-1

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Presentations 1

  1. 75As NMR studies on the nematic state in the iron pnictide NaFeAs International conference

    Masayuki Toyoda, Yoshiaki Kobayashi, Masayuki Itoh

    International conference on Strongly correlated electron systems 2016 

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    Event date: 2016.5

    Language:English   Presentation type:Poster presentation  

    Venue:Hangzhou, China   Country:China  

KAKENHI (Grants-in-Aid for Scientific Research) 11

  1. Study on novel physical properties of quantum materials with multi-orbital electron systems

    Grant number:19H01837  2019.4 - 2023.3

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    Authorship:Coinvestigator(s) 

  2. Investigation on novel quantum phases appeared between itinerant and localized regions in multi-orbital electron systems

    Grant number:16H04012  2016.4 - 2019.3

    Itoh Masayuki

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    Strongly correlated multi-orbital d electron systems between itinerant and localized regions show novel quantum phenomena due to the multi-orbital effect. In this study we have performed characteristic nuclear magnetic resonace (NMR) experiments such as orbital-resolved NMR to understand the phenomena of the strongly correlated electron systems. We obtained interesting results of electronic phase diagram of a superconducting system, charge order in a one-dimensional conductor, nematic order and fluctuation in iron-based superconductors, electronic states of a spin-crossover material, hidden order in a degenerated electron system, magnetic excitations in a candidate of the Kitaev spin liquid, and high-pressure properties of an excitonic-insulator candidate.

  3. Resaerch for Excitonic Insulators

    Grant number:16K13835  2016.4 - 2018.3

    Itoh Masayuki

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    An excitonic insulator is a novel insulator driven by the exciton condensation. We have nuclear magnetic resonance (NMR) measurements to probe the exciton condensation. For a candidate of the excitonic insulator Ta2NiSe5, we observed the characteristic temperature dependences of the Se nuclear spin-lattice relaxation rate and the local magnetic susceptibility coming from the exciton condensation. Thus NMR is concluded to be a useful probe to study the excition condensation in excitonic insulators.

  4. Observation of local orbital states and their role for the electronic state

    Grant number:15K05167  2015.4 - 2018.3

    Kobayashi Yoshiaki

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    Authorship:Principal investigator 

    Grant amount:\4810000 ( Direct Cost: \3700000 、 Indirect Cost:\1110000 )

    Nematic fluctuation was investigated from 75As nuclear magnetic resonance for the iron based superconductors Ba(Fe1-xCox)2As2, NaFeAs, and LiFeAs. We found that the electric nematic fluctuation obtained from Raman scattering can be monitored from the temperature and x dependence of the in-plane anisotropy (eta) of the electric field gradient at the As nuclear position. The eta for all samples shows Curie-Weiss type temperature dependence, where the fitting parameters, C_eta and T_eta, which correspond to Curie constant and the Weiss temperatures, respectively, systematically have x-dependences. The T_eta’s show roughly ~ Ts-50 (K) in x <0.05 where the nematic order emerges (Ts is nematic ordered temperature). Similarly with the result of Raman scattering, the T_eta becomes zero with x~0.055. At x>0.055, we found that the T_eta’s become negative, suggesting the existence of antiferro-type orbital fluctuation.

  5. Study on novel physical properties due to competion or cooperation among degrees of freedom in strongly correlated electron systems with multi-orbitals

    Grant number:24340080  2012.4 - 2015.3

    ITOH Masayuki

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    Strongly correlated 3d electron systems have novel physical properties due to the competition or cooperation among degrees of freedom. In this study, we have investigated localized or itinerant electron systems with multi-orbitals located in the vicinity of the metal-insulator transition to clarify the mechanism of the novel physical phenomena. We found rich physics of heavy fermion, orbital order, frustration, Fe-based superconductivity, and so on in the 3d transition metal oxides and compounds.

  6. Origin of non-superconducting phase by which the superconducting phase were divided.

    Grant number:20540354  2008 - 2010

    KOBAYASHI Yoshiaki

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    Authorship:Principal investigator 

    Grant amount:\4550000 ( Direct Cost: \3500000 、 Indirect Cost:\1050000 )

    The superconductivity of the layered cobalt oxides appears in the phase diagram of T-v_Q (or -the lattice parameter c), where the v_Q is Co nuclear electronic quadrupole resonance frequency. In this phase diagram, the non-superconducting (SC) phase appears to divide the SC phase into two regions. To investigate the nature of the non-SC phase, we have measured the T-dependences of various physical properties. The results are consistently understood by the non-SC phase to be not in the magnetic ordered state but in the charge disproportionate state. Although the existences of multi-SC phases and non-SC phase were explained by changing of the relative energy level between a_<1g>-band and e_g'-band of this layered cobalt oxide, we found that the possibility was excluded by those results, for example, the v_Q (or c) dependence of the electronic specific heat coefficient, NMR Knight shift, and the q-dependence of magnetic excitation by neutron scattering measurements. As the non-magnetic impurity does not suppressed the superconductivity, and NMR Knight shift supports the spin-singlet pairing formation, the SC pairing is considered to be formed mainly by electron-phonon interaction, and it is considered that the transition to non-SC phase suppresses the superconductivity though the decreases of the density of states at Fermi level.
    Next, we have studied the Fe-based superconductors with ten times as large as T_c for the layered cobalt oxides. Non-magnetic impurity effect on T_c for Fe system was found to be very weak as well as the Co-oxides, indicating that the Fe system is found to give an opportunity to perform comparative studies with the layered cobalt oxides.

  7. Magnetic Frustration of Spin 1/2 Pyrochlore Compound

    Grant number:18540346  2006 - 2007

    YASUI Yukio

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    The magnetic behavior in the low temperature region and the ground state of the quantum spin system with magnetically frustrated remain open problem theoretically and experimentally. Pyrochlore compound Hg_2Cu_2FeS has Cu^2+ ions with S=1/2, which consists of a 3-dimensional linkage of corner-sharing Gu_4 tetrahedra, and the Weiss temperature θ_w estimated from the temperature (T) dependence of the magnetic susceptibility is〜150 K, indicating the interaction between the Cu^2+ pins is antiferromagnetic. From these facts, this system is regarded as an ideal example of the geometrically frustrated quantum spins systems. The measurements of the magnetic susceptibility and specific heat as well as neutron diffraction studies have been carried out on the polycrystalline samples of Hg_2Cu_2F_6S. No magnetic transition has been observed in the temperature range clown to 2 K, indicating that the magnetic frustration is not released down to the lowest temperature. To extract microscopic information of the magnetic behavior ; we have also carried out ^19F-NMR, Above〜100K the Knight shift roughly obeys the following Curie Weiss law. With decreasing T from〜100K, the Knight shift has a broad maximum at around 80K, and with further decreasing T, the Knight shift decreases significantly. We cannot distinguish if the Knight shift (spin component of the magnetic susceptibility) approaches zero or not, as Tapproaches zero, because of the increase in the width of the NMR spectra. The magnetic correlation length ξ is estimated by comparing the observed spin-lattice relaxation rate divided T,1/ (T_1T) with the theoretical result obtained by Ganals, et. al. for a 1/2 spin system on the pyrochlore lattice. The values of 1/ (T_1T) and increase gradually with decreasing T, and as the temperature is lowered, ξ increases to a value approximately equal to the Cu-Cu atomic distance. It is interesting that these behaviors seem to correspond to the characteristics of spin system with the geometrical frustration. Because the broadening of the NMR spectra induced by the effects of impurities and/or defects is observed in the low temperature region, it is required to be synthesized the higher purity sample. However, it is not easy to see the intrinsic behavior without the disturbance of the extrinsic effects such as lattice defects and/or impurities, because just a small perturbation brings about rather serious efforts on systems with large degeneracy, which steins from their geometrical characteristics.

  8. Metal-insulator transition near the superconducting phase of two-dimensional cobalt oxides

    Grant number:17540323  2005 - 2006

    KOBAYASHI Yoshiaki

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    Authorship:Principal investigator 

    Grant amount:\3300000 ( Direct Cost: \3300000 )

    We have produced principally three results, which are of considering importance to the mechanism of the formation of the Cooper pairs in Na_xCoO_2・yH_2O superconductors.
    (1) We have revealed that the superconducting pairs in the superconducting state of Na_xCoO_2・yH_2O are in the spin-singlet state, by the measurements of the ^<59>Co-NMR Knight shift for both magnetic field (H) directions parallel and perpendicular to the CoO_2planes in the superconducting state using single phase single crystals.
    (2) The superconducting transition temperatures T_c of Na_xCoO_2・yH_2O have been found to exhibit the systematic dependence on the ^<59>Co nuclear electric quadrupole resonance frequency ν_Q. In the T-3ν_Q phase diagram, the superconducting region of 3ν_Q, spreading over the region between 〜12.0 and 〜12.9 MHz, is divided into two regions by the non-superconducting phase between 〜12.5 and 〜12.6 MHz.
    We have investigated the origin of the non-superconducting phase by detailed experimental measurements of ^<59>Co-NQR and ^2D-NMR and found that the non-superconducting phase is in the charge-density-wave (CDW) or the charge disproportionate state, in which the magnetic moments induced inhomogeneously by this transition become frozen at low temperatures.
    (3) We have revealed that the x dependence of the electronic nature of Na_x,CoO_2 which is the parent compound of Na_<0.3>CoO_2・1.3H_2O superconductors. In particular, the successive phase transitions observed in Na_<0.5>CoO_2 at 87 K (T_<c1>) and 53 K (T_<c2>) have been studies. Na_<0.5>CoO_2 indicates the antiferromagnetic ordering below T_<c1>, where we have determined the unusual magnetic structure by ^<59>Co-NMR and neutron diffraction studies.
    It has been found from the X dependence of χ-T and 1/T_1-T curves that the two-dimensional nature of the electrons of Na_xCoO_2 is enhanced and the antiferromagnetic correlation increases in this system as the Na concentration x decreases. Therefore, the superconducting pairs are expected to be in the singlet state. This is consistent with the results of the Knight shift studies in Na_<0.3>CoO_2-1.3H_2O.

  9. Control of the Electronic State of Co Oxides and Studies on Novel Superconductivity

    Grant number:16204025  2004 - 2007

    SATO Masatoshi

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    Many systems with strongly correlated electrons have been synthesized and their physical properties have been studied to find "unusual" or "anomalous" physical properties which are useful for development of novel physical concepts. In the studies, we synthesized materials and characterized them first, and then, studied their macroscopic properties. If they seemed to have physically attractive nature, experimental methods, such as NMR and neutron scattering, were applied to further study it microscopically, where knowledge accumulated in the past two decades in the study of high To Cu oxides were used as the guide line of the works. In the microscopic studies, we often used single crystals prepared by ourselves, which made us possible to obtain quite reliable experimental results. The main subjects on which we could make significant achievements are ; (1) several problems which remained in the studies of high-T, superconductivity of Cu oxides, (2) mechanism of the superconductivity of Na_xCo0_2 yH_2O (y〜3), (3) unusual behavior of the anomalous Hall effect observed in nontrivial magnetic structures such as Nd_2Mo_2O_2 and spin-glass system, (4) spin liquid state of the quantum spins in pyrochlore system Hg_2Cu_2F_6S, (5) control of the spin state of Co ions in perovskite and related systems, (6) a spin gap phenomenon and a new type phase transition found in(pseudo)honeycomb systems, (7) search for multiferroics and detailed studies of multiferroic phenomenon found in systems with CuO_2 ribbons having simple spin 1/2 Cu^2+ chains, and so on. In the studies of these systems, preparation or syntheses of the systems and finding new physical phenomena are closely connected. For the further description of the achievements, we add the following as the examples. In the study of the superconductivity, we have shown that the Cooper pairs are in the singlet state, excluding predictions of many theoretical works as well as results of experimental studies carried out in the same period by other groups. We have presented complete T_c-v_Q phase diagram (v_Q : NMR quadrupole frequency), and also obtained key information on the dynamical magnetic behavior by neutron inelastic scattering of the superconductor. On the controversy if Nd_2Mo_2O_7 is the unique example of systems which exhibit the unusual anomalous Hall effect induced by the spin chirality mechanism, we have excluded such the possibility quite clearly by detailed neutron diffraction studies. To find the realization of the chirality mechanism of the anomalous Hall effect at least in periodic system remains as the future subject Our discovery of the multiferroic system LiVCuO_4 has presented a new attractive example with spin 1/2 quantum spin chains 'with helical structure, which is simple and convenient for the detailed study on the characteristics of the multiferroic behavior

  10. Metal-insulator transitions induced by pressure for perovskite cobalt oxides

    Grant number:15540336  2003 - 2004

    KOBAYASHI Yoshiaki

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    Authorship:Principal investigator 

    Grant amount:\3700000 ( Direct Cost: \3700000 )

    Cobalt oxides with network of CoO_6 octahedra have attracted interest, because they exhibit various notable physical characteristics. The main subject of this research is the search of the method to control the electronic state of the cobalt oxides. We have studied (1)the mechanisms of the metal-insulator(M-I) transition of the perovskite cobalt oxide Pr_<1-x>Ca_xCoO_3 and (2)the symmetry of the superconducting order parameter of a cobalt oxide superconductor Na_xCoO_<2-y>H_2O.
    (1)The structural studies and the magnetic and transport measurements have been carried out on (Pr_<1-y>R_y)_<1-x>Ca_xCoO_3(R=rare earth elements and Y) at ambient pressure and high pressure. The intimate relationship between the local structure around the Co ions and the electronic (or spin) state of Co^<3+> ions has been discussed. We have found that both the Pr and Co atoms are necessary for the occurrence of the M-I transition, which implies that the Pr 4f-O 2pπ hybridization may be relevant to the occurrence of the transition.
    (2)Measurements of ^<59>Co-NMR Knight shift K and nuclear magnetic relaxation rate 1/T_1 have been carried out. Studies of the impurity effect on the superconducting transition temperature T_c have also been carried out on Na_xCoO_<2-y>H_2O. For the magnetic field directions, H‖ and ⊥ CoO_2 plane, K decreases below the T_c(H) with decreasing T, indicating that the superconducting electron pairs are in the singlet state. The negligibly small coherence peak of the 1/T_1T-T curve indicates, at first sight, that the superconducting order parameter has a node. However, the small effect of nonmagnetic impurities on T_c cannot simpty be explained by such kinds of anisotropic order parameter. Now, it is important to understand these results consistently. One possible way is, we speculate, to consider effects of quasi-particle broadening in s-wave superconductors because the broadening brings about the negligibly small coherence peak.

  11. Anomalous Physical Properties of Strongly Correlated Electron System with Frustration and Spin Chirality

    Grant number:14340103  2002 - 2003

    SATO Masatoshi

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    Studies focused mainly on strongly correlated electrons with geometrical frustration have been carried out. (i)Unusual behaviors of the anomalous Hall resistivity(AHR) of ferromagnetic systems with non-trivial magnetic structure have been studied to clarify if the behavior is related to the ordering of spin chirality χ locally defined for three spins S_1, S_2 and S_3 as χ≡S_1(S_2×S_3). Ground states of frustrated spin systems have been studied experimentally for various pyrochiore type oxides. (ii) Superconductivity of Na_xCoO_2・yH_2O has been studied mainly by means of NMR. (iii)We have also studied the physics of high-T_c Cu oxides mainly by studying the characteristics of their magnetic excitation spectra.
    To see the origin of unusual behaviors of AHR of Nd_2Mo_2O_7, the magnetic structure has been analyzed as a function of the applied magnetic field Hand the H-dependence of the chirality (or AHR) has been directly calculated from the obtained results. Mo→Ti substitution effects on the behaviors of the AHR has also been studied. The results of these studies clearly indicate that the chiral order mechanism proposed theoretically does not, at least, have a primary role in determining the behavior of the AHR of Nd_2Mo_2O_7. In the study on AHR of a reentrant spin glass system Fe_<1-x>Al_x, it has been shown that the uniform chirality induced by the coupling of the frozen chirality with the uniform magnetization contributes to AHR. In the study on so-called spin ice system, Ho_2Ti_2O_7, we hav.e shown what kind of spin correlation this strongly frustrated spin system has at T→0.
    To clarify if the superconductivity of Na_xCoO_2・yH_2O with triangular lattice of CoO_2, The NQR 1/T_1T and the NMR Knight shift K have been measured, where a very small (or no) coherence peak of 1/T_1T and the decrease of K have been observed. Extensive studies are now being carried out.

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Teaching Experience (On-campus) 11

  1. Condensed matter physics III

    2015

  2. 電磁気学 I

    2015

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    電磁気学の基礎を習得するための講義である。真空中の電磁気現象及びそれを支配する法則の習得を通じて「真空」や「場」の基礎概念、物理学における数学的取り扱いの基礎を学ぶとともに、電磁気現象の豊かさに触れる。

  3. 電磁気学 II

    2016

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    1年後期の「電磁気学I」に引続き、電磁気学の基礎を習得するための講義である。真空中、物質中の電磁気現象及びそれを支配する法則の習得を通じて「真空」や「場」の基礎概念、物理学における数学的取り扱いの基礎を学ぶとともに、電磁気現象の豊かさに触れる。

  4. Foundations of Electromagnetics II

    2020

  5. Physics Tutorial I

    2020

  6. Science of Materials

    2020

  7. Special Lectures on Condensed Matter Physics and Biophysics

    2020

  8. 電磁気学II

    2019

  9. 物理学演習Ⅳ

    2012

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    統計物理学演習

  10. First Year Seminar A

    2012

  11. First Year Seminar A

    2011

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Social Contribution 1

  1. 日本物理学会第75回年次大会(2020年)運営委員

    Role(s):Organizing member

    一般社団法人 日本物理学会  2020.3