The extended Hubbard model applied to phase diagram and the pressure effects in Bi2Sr2CaCu2O8+y superconductors

We use the two dimensional extended Hubbard Hamiltonian with the position o f the attractive potential as a variable parameter, within a BCS type appro ach, to study the interplay between the superconductor transition temperatu re T-c and hole content for high temperature superconductors. This method g ives some insight on the range and intensity of the Cooper pair interaction . It suggests why different compounds have different values for their measu red coherence lengths, and describes the experimental results of the superc onducting phase diagram T-c x n. The calculations may also be used to study the effect of the applied pressure with the assumption that it increases t he attractive potential which is accompanied by an increase in the supercon ductor gap. In this way we obtain a microscopic interpretation for the intr insic term and a general expansion for T-c in terms of the pressure which r eproduces well the experimental measurements on the Bi2Sr2CaCU2O8+y superco nductors.