RIGOROUS RESULTS ON SUPERCONDUCTING GROUND-STATES FOR ATTRACTIVE EXTENDED HUBBARD MODELS

We show that the exact ground state for a class of extended Hubbard mo dels including bond-charge, exchange, and pair-hopping terms, is the Y ang ''eta-paired'' state for any nonvanishing positive value of the pa ir-hopping amplitude, at least when the on-site Coulomb interaction is attractive enough and the remaining physical parameters satisfy a sin gle constraint. The ground state is thus rigorously superconducting. O ur result holds on a bipartite lattice in any dimension, at any band f illing, and for arbitrary electron hopping.