title: Gutzwiller variational theory for the Hubbard model with attractive interaction.
abstract: We investigate the electronic and superconducting properties of a negative-U Hubbard model. For this purpose we evaluate a recently introduced variational theory based on Gutzwiller-correlated BCS wavefunctions. We find significant differences between our approach and standard BCS theory, especially for the superconducting gap. For small values of |U|, we derive analytical expressions for the order parameter and the superconducting gap which we compare to exact results from perturbation theory.
authors.affiliation: Fachbereich Physik, Philipps-Universität Marburg, D-35032 Marburg, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Bünemann
authors.forename: Florian
authors.initials: F
authors.lastname: Gebhard
authors.forename: Katalin
authors.initials: K
authors.lastname: Radnóczi
authors.forename: Patrik
authors.initials: P
authors.lastname: Fazekas