2006 Fiscal Year Final Research Report Summary
Theory for New Mechanism of Superconductivity with Repulsive Origin and Local Quantum Critical Phenomena
| Project/Area Number |
16340103
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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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 | Osaka University |
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Principal Investigator |
MIYAKE Kazumasa Osaka University, Graduate School of Engineering Science, Professor, 大学院基礎工学研究科, 教授 (90109265)
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| Co-Investigator(Kenkyū-buntansha) |
KOHNO Hiroshi Osaka University, Gracluale School of Engineering Science, Associate Professor, 大学院基礎工学研究科, 助教授 (10234709)
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| Project Period (FY) |
2004 – 2006
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| Keywords | strongly correlated electron systems / anisotropic superconductivity / f^2-based heavy fermions / numerical renormalization group / quantum critical phenomena / crystalline-electric-field effect / critical valence fluctuations |
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| Research Abstract |
1) We succeeded in understanding the superconducting state of quasi-one dimensional systems, such as (TMTSF)_2PF_6 and Sr_2Ca__<12>CU_<24>O_<41> by analyzing the pairing interaction by perturbation renormalization group (PRG) method.
2) In order to clarify the properties of quasi-particle interaction of heavy fermion based on f^2- electronic configuration, we studied its impurity model by the numerical renormalization group (NRG) method, and showed that the inter-orbital interaction can dominate over the intra-orbital one. This gives us a clue to understand a microscopic mechanism of superconductivity of f^2-based heavy fermions, such as UPt_3.
3) Kondo effect in a metal at antiferromagnetic quantum critical point (AFQCP) is studied by two-loop PRG method. It is found that the fixed point of multichannel Kondo effect exists robustly if the Fermi surface has hot-spot (s) or hot-line (s) corresponding to the antiferromagnetism. This gives a microscopic basis for the so-called local quantum
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critical phenomena observed around AFQCP of some heavy fermion compounds.
4) We proposed a new microscopic model for spin-triplet superconductor Sr_2RuO_4 in which the effective hybridization between 4d at Ru-site and 2p at O-site, making the weight of 2p electrons non-negligible in the quasiparticle band. It is found that the short-ranged ferromagnetic correlations caused by on-site repulsion at O-site can easily give rise to spin-triplet pairing even in 2nd-order perturbation calculation for the paring interaction.
5) In order to investigate the quantum critical transition of valence of Ce and its effect on the unconventional superconductivity observed in heavy fermion compounds CeCu_2(Si, Ge)_2, we studied an extended Anderson model with U_<fc>, Coulomb repulsion between f-and conduction electrons in one dimensional system, and found that the tendency of off-site superconducting pairing becomes dominant around parameter region where the valence exhibits sharp crossover from the Kondo to the valence fluctuation regime.
6) We investigated the effect of crystalline-electric-field in Ce-based heavy fermion by means of 1/N-expansion method of a la Nagoya and NRG method of Wilson, and found that it causes great influences on temperature dependences of the resistivity under pressure and the valence transition of Ce ion. Less
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