Electron pairing in the negative- U Hubbard narrow energy band model

Abstract

Starting from the negative- U Hubbard model, an approximate expression is derived for the generalized energy gap function Δ kμ for a system of interacting electrons in a narrow s-band. This function has the virtue that it interpolates between the weak interaction limit (BCS) and the intermediate coupling regime. Starting from the Cooper pairing state, we investigate the build up of pairing correlations and study the properties gap in the weak and intermediate interaction limits as a function of electron density. The coupled equations for the gap Δ kμ and the electron density define the self-consistency condition.