| Project/Area Number |
03640306
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性
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| Research Institution | Nagoya University |
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Principal Investigator |
KURODA Yoshihiro Nagoya Univ., Physics Dept., Professor, 理学部, 教授 (60013504)
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| Co-Investigator(Kenkyū-buntansha) |
HIRASHIMA Dai Tsukuba Univ., Inst. of Physics, Assistant Professor, 物理学系, 講師 (20208820)
ONO Yoshiaki Nagoya Univ., Physics Dept., Research Associate, 理学部, 助手 (40221832)
MATSUURA Tamifusa Nagoya Univ., Physics Dept., Associate Professor, 理学部, 助教授 (10022609)
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| Project Period (FY) |
1991 – 1993
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| Project Status |
Completed (Fiscal Year 1993)
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| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1993: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1992: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1991: ¥800,000 (Direct Cost: ¥800,000)
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| Keywords | high-T_c superconductors / strongly correlated electrons / charge fluctuation / d-p model / (1 / N)-expansion theory / Fermi liquid / marginal Fermi liquid / Neel order / 酸化物高温超伝導 / I / N-展開理論 / 高濃度近藤合金 / 強相関 / 重い電子 / 高温超伝導 / アンダ-ソン模型 / dーp模型 / N展開理論 / フェルミ液体 / 高密度近藤系 |
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| Research Abstract |
The main aim of this research project is, as one of the clues to clarify the mechanism for obtaining the high-T_c superconductor, to investigate roles of charge fluctuation in the d-p model which is believed to describe the strongly correlated electrons in the CuO_2 2-dimensional electron systems well.
1. Firstly we applyed the 1/N-expansion theory to study propertie of the impurity Anderson model and the lattice Anderson model which have been known to some extent, have clarified the roles of the charge fluctnation and confirmed the usefullness of the 1/N-expansion theory.
2. Secondly we employed the 1/N-expansion theory to investigate properties of the d-p model and have found the charge fluctuation to play important roles for determining the properties of the high-T_c superconductors as follows :
(a)At lower temperatures(T<T_0)where T_0 is the so-called coherence temperatute, hole doping creates some new stable quasiparticle states inside the charge transfer energy gap(called as ingap states)and the system behaves as a Fermi liquid. By denoting the band width of the ingap states omega_0, T_0 is given by T_0 (〕SY.simeq.〔) 0.1omega_0.
(b)At intermediate temperatures, (T_0<T<omega), the system behaves as a marginal Fermi liquid, where the quasi-particle life time is proportional to 1/T and the magnetic susceptibility shows cross-over from the Pauli Paramagnetism to the Curie law.
(c)The Coulomb repulsion between electrons at the nearest Cu and O sites enhances the charge fluctuation, the exchange interaction between electrons at the nearest Cu sites stabilizes the antiferromagnetic order in the ingap states and the direct transfer between electrons at the nearest O sites may modify the properties of the systems significantly.
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