Superconducting critical temperature, for s-wave symmetry order parameter,for intermediate correlated electron systems

We calculate the superconducting critical temperature, T-c, for an s-wave o rder parameter, in the presence of local Coulomb interactions by using a no rmal state one particle Green function, G(N)((k) over right arrow ,i omega (n)), which is renormalized by the interactions. In the end, we adopt for G (N)((k) over right arrow ,i omega (n)) a Hubbard-III like approximation sin ce it can give a normal metal-insulator transition and as such can be used to study T-c vs. U for intermediate values of U, going beyond the mean-fiel d treatment for the local Coulomb interaction, U. However, the equation for T-c is mean-field like with respect to the pairing interaction, V, which w e assume with a different origin than the repulsive part. We have calculate d. (1) T-c vs. U for different values of V and chemical potential, mu; (2) T-c vs. rho dropn/2 for different values of V and U. The conclusions we rea ch are: (a) the local Coulomb interaction is always detrimental to supercon ductivity, namely, T-c goes down with increasing U; (b) the maximum value o f T-c is reached away from half-filling, contrary to the pure BCS-case (U d rop 0). Results (a) have also been obtained in non-Fermi liquid theories. W e have compared our results with known relevant work. (C) 2001 EIsevier Sci ence B.V. All rights reserved.