| Project/Area Number |
18540348
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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 | Ritsumeikan University |
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Principal Investigator |
YAMADA Kosaku Ritsumeikan University, Faculty of Science and Engineering, 研究員 (90013515)
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| Project Period (FY) |
2006 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥1,230,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥30,000)
Fiscal Year 2007: ¥130,000 (Direct Cost: ¥100,000、Indirect Cost: ¥30,000)
Fiscal Year 2006: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Keywords | High Tc Superconductor / Strong Electrog Correlation / Fermi Liquid / Heavy Electrons / Organic Superconductors / Superconductors in Multi-Band Systems / Renormalization Theory / Anisotropic Sunperconductivity / 強相関 / 超伝導転移温度 / 4次摂動理論 / 自己エネルギー / 電子相関 / 有効質量 / 繰り込み因子 |
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| Research Abstract |
It is made dear that the superconducting transition temperature is determined by the following competing two effects.
1. Renormalization of effective mass determines the band width of quasiparticles in Fermi liquid states
The Coulomb interaction between electrons enhances the effective mass of electrons. The enhancement arises from the reduction of dispersion in electron bands. The renormalization factor z determines energy scale. For example, heavy electrons possesses 1000times large electron mass compared with free electron. Therefore the band width of quasiparticles is reduced by the factor of 1/1000 and takes the value around 10K On the other hand, the electron mass in cuprates is enhanced around 10 times and the band width of quasiparticles is reduced by 1/10 to 1000K. The superconducting gaps are created in these quasiparticle bands and renormalized by the inverse of quasiparticle mass, z. That is, the superconducting transition temperature is reduced in proportion to the wavefunction renormalization factor z. Thus the strong electron interaction reduces the transition temperature.
2 . The momentum dependence of interaction between quasiparticles determines the symmetry and transition temperature of superconductivity.
The isotropic repulsive force is canceled out by the sign change of gap function and the anisotropic parts of quasiparticle interaction determine the symmetry and transition temperature of superconducting state. In this case strong interaction increases the superconducting transition temperature
The above two effects compete with each other. The former is determined by total interaction including isotropic part, while the latter is determined by dominant anisotropic momentum dependent part of quasiparticle interaction. As a result we can explain the transition temperature quantitatively. In strongly correlated electron systems.
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