Possible Pairing Symmetry of Three-dimensional Superconductor UPt_3 : Analysis Based on a Microscopic Calculation(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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Stimulated by the anomalous superconducting properties of UPt_3, we investigate the pairing symmetry and the transition temperature in the two-dimensional (2D) and three-dimensional (3D) hexagonal Hubbard model. We solve the Eliashberg equation using the third order perturbation theory with respect to the on-site repulsion U. As results of the 2D calculation, we obtain distinct two types of stable spintriplet pairing states. One is the ƒ-wave (B_1) pairing around n=1.2 and in a small U region, which is caused by the ferromagnetic fluctuation. Then, the other is the P_x (or P_y)-wave (E_1) pairing in large U region far from the half-filling (n=1) which is caused by the vertex corrections only. However, we find that the former ƒ-wave pairing is destroyed by introduced 3D dispersion. This is because the 3D dispersion breaks the favorable structures for the ƒ-wave pairing such as the van Hove singularities and the small pocket structures. Thus, we conclude that the ferromagnetic fluctuation mediated spin-triplet state can not explain the superconductivity of UPt_3. We also study the case of the pairing symmetry with a polar gap. This P_z-wave (A_1) is stabilized by the large hopping integral along c-axis t_z. It is nearly degenerate with the suppressed P_x (or P_y)-wave (E_1) in the best fitting parameter region to UPt_3 (1.3≤t_z≤1.5). These two p-wave pairing states exist in the region far from the half-filling, in which the vertex correction terms play crucial roles like the case in Sr_2RuO_4.
社団法人日本物理学会の論文
2005-06-15

Possible Pairing Symmetry of Three-dimensional Superconductor UPt_3 : Analysis Based on a Microscopic Calculation(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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