Study of Superconducting Transition Temperature in d-p Model on Basis of Perturbation Theory(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We investigate the mass enhancement factor and the superconducting transition temperature T_c in the d-p model, to explain differences of T_c observed in the high-T_c cuprates, such as YBa_2Cu_3O<7-δ> (YBCO) and La_<2_x>Sr_xCuO_4 (LSCO). First, we calculate the mass enhancement factor by expanding the normal selfenergy perturbatively up to the fourth order with respect to the on-site repulsion U. The large mass enhancement is obtained when the energy level splitting between the d-level and the p-level is large, which corresponds to LSCO. Next, we calculate T_c by expanding the effective pairing interaction up to the third order and solving the Eliashberg equation in the renormalized quasiparticle scheme. As results, T_c is remarkably suppressed due to the large mass renormalization factor when the level splitting is large. We conclude that the strong correlation in LSCO enhances the pairing interaction but reduces the quasiparticle energy scale more efficiently, and then T_c in LSCO is lower than that in YBCO.
社団法人日本物理学会の論文
2006-10-15