E. Takayama-Muromachi

Publications (6)1.21 Total impact

• Article: Hard-X-ray photoelectron spectroscopy of NaxCoO2 center dot yH(2)O

  A Chainani, T Yokoya, Y Takata, K Tamasaku, M Taguchi, T Shimojima, N Kamakura, K Horiba, S Tsuda, S Shin, [......], Y Nishino, T Ishikawa, M Yabashi, K Kobayashi, H Namatame, M Taniguchi, K Takada, T Sasaki, H Sakurai, E Takayama-Muromachi
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  ABSTRACT: We study the bulk electronic structure of Na(x)CoO(2 center dot)yH(2)O using Hard X-ray (HX, hv = 5.95KeV) synchrotron photoelectron spectroscopy (PES). The Co 2p core level spectra show well-separated Co3+ and Co4+ ions. Cluster calculations suggest low spin Co3+ and Co4+ character, and a moderate on-site Coulomb correlation energy U-dd similar to 3-5.5 eV. Photon-dependent valence band PES identifies Co 3d and 0 2p derived states, in near agreement with band structure calculations. We discuss the importance of HX-PES for studying correlated transition metal oxides. (c) 2005 Elsevier B.V. All rights reserved.
  Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2005; 547(1):163-168. · 1.21 Impact Factor
• Source

  Available from: A. Chainani

  Article: Laser-excited ultrahigh-resolution photoemission spectroscopy of NaxCoO2.yH2O:Evidence for pseudogap formation

  T Shimojima, T. Yokoya, T Kiss, A. Chainani, S Shin, T Togashi, C Chen, S Watanabe, K Takada, T Sasaki, H Sakurai, E. Takayama-Muromachi
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  ABSTRACT: We have studied the temperature-dependent electronic structure near the Fermi level (EF) of the layered cobaltate superconductor, Na0.35CoO2.1.3H2O, and related materials, using laser-excited ultrahigh-resolution photoemission spectroscopy. We observe the formation of a pseudogap with an energy scale of ~ 20 meV in Na0.35CoO2.1.3H2O and Na0.35CoO2.0.7H2O, which is clearly absent in Na0.7CoO2. The energy scale of the pseudogap is larger than the expected value for the superconducting gap, suggesting an additional competing order parameter at low temperatures. We discuss implications of the pseudogap in relation to available transport and magnetic susceptibility results. Comment: 4 pages, 3 figures
  06/2004;
• Article: Bulk electronic structure of Na0.35CoO2 center dot 1.3H(2)O

  A Chainani, T Yokoya, Y Takata, K Tamasaku, M Taguchi, T Shimojima, N Kamakura, K Horiba, S Tsuda, S Shin, [......], Y Nishino, T Ishikawa, M Yabashi, K Kobayashi, H Namatame, M Taniguchi, K Takada, T Sasaki, H Sakurai, E Takayama-Muromachi
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  ABSTRACT: High-energy (hnu=5.95 keV) synchrotron photoemission spectroscopy (PES) is used to study bulk electronic structure of Na0.35CoO2.1.3H(2)O, the layered superconductor. In contrast to three-dimensional doped Co oxides, Co 2p core level spectra show well-separated Co3+ and Co4+ ions. Cluster calculations suggest low-spin Co3+ and Co4+ character, and a moderate on-site Coulomb correlation energy U(dd)similar to3-5.5 eV. Photon dependent valence band PES identifies Co 3d and O 2p derived states, in near agreement with band-structure calculations.
  Physical Review B. 01/2004; 69(18).
• Source

  Available from: Yoshinori Nishino

  Article: Bulk Electronic structure of Na$_{0.35}$CoO$_{2}$.1.3H$_{2}$O

  A. Chainani, T. Yokoya, Y Takata, K. Tamasaku, M Taguchi, T Shimojima, N. Kamakura, K Horiba, S Tsuda, S Shin, [......], Y Nishino, T Ishikawa, M. Yabashi, K Kobayashi, H. Namatame, M Taniguchi, K Takada, T Sasaki, H Sakurai, E. Takayama-Muromachi
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  ABSTRACT: High-energy (h$\nu$ = 5.95 keV) synchrotron Photoemission spectroscopy (PES) is used to study bulk electronic structure of Na$_{0.35}$CoO$_{2}$.1.3H$_{2}$O, the layered superconductor. In contrast to 3-dimensional doped Co oxides, Co $\it{2p}$ core level spectra show well-separated Co$^{3+}$ and Co$^{4+}$ ions. Cluster calculations suggest low spin Co$^{3+}$ and Co$^{4+}$ character, and a moderate on-site Coulomb correlation energy U$_{dd}\sim$3-5.5 eV. Photon dependent valence band PES identifies Co $\it{3d}$ and O $\it{2p}$ derived states, in near agreement with band structure calculations. Comment: 4 pages 4 figures Revised text added reference
  12/2003;
• Article: Laser-excited ultrahigh-resolution photoemission spectroscopy of Na_ {x} CoO_ {2}· yH_ {2} O: Evidence for pseudogap formation

  T. Shimojima, T. Yokoya, T. Kiss, A. Chainani, S. Shin, T. Togashi, S. Watanabe, C. Zhang, C. T. Chen, K. Takada, T. Sasaki, H. Sakurai, E. Takayama-Muromachi
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  ABSTRACT: We have studied the temperature (T)-dependent electronic structure near the Fermi level of the layered cobaltate superconductor, Na0.35CoO2·1.3H2O, and related materials, using laser-excited ultrahigh-resolution photoemission spectroscopy. We observe the formation of a pseudogap (PG) with an energy scale of ∼20 meV in Na0.35CoO2·1.3H2O and Na0.35CoO2·0.7H2O, which is clearly absent in Na0.7CoO2. The energy scale of the PG is larger than the expected value for the superconducting gap, suggesting an additional competing order parameter at low T. We discuss implications of the PG in relation to available transport and magnetic susceptibility results.
  Phys. Rev. B. 71(2).
• Article: Bulk electronic structure of Na_ {0.35} CoO_ {2}⋅ 1.3 H_ {2} O

  A. Chainani, T. Yokoya, Y. Takata, K. Tamasaku, M. Taguchi, T. Shimojima, N. Kamakura, K. Horiba, S. Tsuda, S. Shin, [......], Y. Nishino, T. Ishikawa, M. Yabashi, K. Kobayashi, H. Namatame, M. Taniguchi, K. Takada, T. Sasaki, H. Sakurai, E. Takayama-Muromachi
  [show abstract] [hide abstract]
  ABSTRACT: High-energy (hν=5.95keV) synchrotron photoemission spectroscopy (PES) is used to study bulk electronic structure of Na0.35CoO2⋅1.3H2O, the layered superconductor. In contrast to three-dimensional doped Co oxides, Co 2p core level spectra show well-separated Co3+ and Co4+ ions. Cluster calculations suggest low-spin Co3+ and Co4+ character, and a moderate on-site Coulomb correlation energy Udd∼3–5.5eV. Photon dependent valence band PES identifies Co 3d and O 2p derived states, in near agreement with band-structure calculations.
  Phys. Rev. B. 69(18).