The Hubbard model and pressure effects of YBa 2Cu 3O 7− δ superconductors

Abstract

We apply a mean field approach to the extended Hubbard model on a square lattice to the YBa 2Cu 3O 7− δ family of superconductors under pressure. The parameters of the tight-binding band are taken from experiments, and the coupling strength U and V are estimated by the zero pressure phase diagram ( T c× n h). This scheme yields the non-trivial dependence of the superconductor critical temperature T c as a function of the hole concentration n h in the CuO 2 plane. With the assumption that the pressure P modifies the potential V and the on-plane hole content n h, we can distinguish the charge transfer and the intrinsic contribution to T c( P). We show that the changes on T c( P) for the YBa 2Cu 3O 7 optimally doped compound at low pressures are almost entirely due to the intrinsic term.