Superconducting Properties of La_2−xSr_xCuO₄ within the Framework of the Phonon Mediated Pairing Mechanism

Abstract

Superconducting properties of La_2−xSr_xCuO₄ are investigated theoretically within the framework of the phonon mediated pairing mechanism by solving the linearized Eliashberg equation, based on the electronic structure derived by Kamimura and Eto, in which holes are mainly accommodated in the Cu dz² and O-p hybridized upper Hubbard band in a superconducting phase. Effective electron-phonon coupling constant λ is estimated as 0.46 by fitting the calculated T-dependence of resistivity to the experimental data by Takagi et al. Then T_c is calculated by using the energy dispersion of the dz² upper Hubbard band. The calculated x-dependence of T_c agrees well with the experimental result by Torrance et al. The x-dependences of an isotope effect, the energy gap parameter, the heat capacity jump at T_c and the penetration depth are also calculated. The origin of a high T_c value is due to the occurrence of a sharp peak in the density of states of the dz² upper Hubbard band.