| Project/Area Number |
15540336
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics II
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| Research Institution | Nagoya University |
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Principal Investigator |
KOBAYASHI Yoshiaki Nagoya University, Graduate School of Science, Lecturer, 大学院・理学研究科, 講師 (60262846)
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| Co-Investigator(Kenkyū-buntansha) |
SATO Masatoshi Nagoya University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (40092225)
YASUI Yukio Nagoya University, Graduate School of Science, Assistant Professor, 大学院・理学研究科, 助手 (80345850)
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| Project Period (FY) |
2003 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2004: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2003: ¥2,800,000 (Direct Cost: ¥2,800,000)
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| Keywords | Cobalt oxide / Metal-Insulator transition / spin state change / Magnetic and transport properties / superconductivity / nuclear magnetic resonance / Knight shift / impurity effects on superconducting transition temperature / Pr_<1-x>Ca_xCoO_3 / 磁気輸送特性 / Na_xCoO_2・_yH_2O / 核磁気共鳴緩和率 / 超伝導転移温度への不純物効果 / ホールドーピング / Na_xCoO_2・yH_2O / 核磁気緩和率 |
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| Research Abstract |
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.
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