The Hubbard model and pressure effects of YBa2Cu3O7-δ superconductors

We apply a mean field approach to the extended Hubbard model on a square lattice to the YBa2Cu3O7-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 (Tcxnh). This scheme yields the non-trivial dependence of the superconductor critical temperature Tc as a function of the hole concentration nh in the CuO2 plane. With the assumption that the pressure P modifies the potential V and the on-plane hole content nh, we can distinguish the charge transfer and the intrinsic contribution to Tc(P). We show that the changes on Tc(P) for the YBa2Cu3O7 optimally doped compound at low pressures are almost entirely due to the intrinsic term