EXTENDED HUBBARD-MODEL APPLIED TO STUDY THE PRESSURE EFFECTS IN HIGH-TEMPERATURE SUPERCONDUCTORS

We make use of a BCS-type approach based on the extended Hubbard Hamil tonian to study the superconductor transition and to give a microscopi c interpretation of the pressure effects on T-c in high-temperature su perconductors. This method suggests that the applied pressure causes a n increase of the superconducting gap and this effect is explored in o rder to explain the variations of T-c. Our approach is therefore beyon d the scope of previous phenomenological models which basically postul ate a pressure-induced charge transfer and an intrinsic term linear in pressure. We obtain a microscopic interpretation of this intrinsic te rm and a general expansion of T-c in terms of the pressure. To demonst rate the efficiency of the method we apply it to the experimental data of the Hg-based superconductors.