Eur. Phys. J. B 12, 387-391 (1999)
https://doi.org/10.1007/s100510051019

Superconductivity in weakly correlated electron systems

Institut für Theoretische Physik, Universtät Bremen, Postfach 330 440, 28 334 Bremen, Germany

Corresponding author: ^a czycholl@theo.physik.uni-bremen.de

Received: 17 February 1999
Published online: 15 December 1999

Abstract

We study the influence of the short-ranged Hubbard correlation U between the conduction electrons on the Cooper pair formation in normal (s-wave) superconductors. The Coulomb correlation is considered within the standard second order perturbation theory, which becomes exact in the weak coupling limit but goes beyond the simple Hartree-Fock treatment by yielding a finite lifetime of the quasiparticles at finite temperature. An attractive pairing interaction V, which may be mediated by the standard electron-phonon mechanism, is considered between nearest neighbor sites. A critical value V_c for the attractive interaction is required to obtain a superconducting state. For finite temperature a gapless superconductivity is obtained due to the finite lifetime of the quasiparticles, i.e. the Coulomb correlation has a pair-breaking influence. The energy gap Δ and T_c depend very sensitively on U, V and band filling n and develop a maximum away from half filling as function of n. The ratio varies with n, being higher than the BCS value near half filling and reaching the BCS value for lower n.