| Project/Area Number |
17540316
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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 | The University of Electro-Communications |
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Principal Investigator |
KUROKI Kazuhiko The University of Electro-Communications, Faculty of Electro-Communications, Professor (10242091)
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| Project Period (FY) |
2005 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥2,610,000 (Direct Cost: ¥2,400,000、Indirect Cost: ¥210,000)
Fiscal Year 2007: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2006: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2005: ¥900,000 (Direct Cost: ¥900,000)
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| Keywords | Na_xCoO_2 / Pr_2Ba_4Cu_7O_<15-δ> / (TMTSF)_2X / spin fluctuations / charge fluctuations / superconductivity / thermopower / band structure / フェルミ面 / バンド構造 / 磁性 / ペアリング対称性 / コバルト酸化物 / 分子性結晶 / FLEX近似 |
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| Research Abstract |
1. We have proposed that superconductivity, magnetism, and large thermopower observed in NaxCoO2 share the same origin, namely, the peculiar shape of the a1g band. Pairing in superconductivity is mediated by the spin fluctuations originating from the nesting between the inner and outer Fermi surfaces, which appear due to the local minimum structure of the a1g band at the F point. The coexistence of spin and charge fluctuations results in an extended s-wave pairing in which the gap changes sign between the inner and the outer Fermi surfaces, but has the same sign within each Fermi surface. Magnetism also occurs due to the same nesting but with more three dimensionality. The coexisting large thermopower and low resistivity originate from the overall "pudding mold" shape of the band.
2. It is considered that superconductivity in Pr2Ba4Cu7O15-δ occurs within the double-chain structure. We have adopted a realistic model that reproduces the first principles band calculation, and obtained an extended s-wave like superconductivity with Tc ~20K at a wide range of band filling, which is mediated by spin fluctuations due to the on-site repulsion and the nesting between multiple Fermi surfaces peculiar to this system. We have also found that the nearest neighbor interaction is necessary in order to reproduce the oxygen content dependence of T.
3. We have studied the competition of spin singlet and triplet superconductivity in a model for a organic superconductor(TMTSF) 2X. We have found that the coexistence of spin and charge fluctuation results in a subtle competition between singlet and triplet pairings, and the latter may dominate in a realistic parameter regime. We have also found that the magnetic field strongly enhances triplet pairing that occurs due to coexisting spin and charge fluctuations.
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