-pairing superconductivity in generalized Hubbard models

We consider generalized Hubbard models in arbitrary dimensions which have additional nearest-neigbour interactions. It is shown that in a large region of the parameter space these models have ground states of the-pairing type. These ground states exhibit oo-diagonal long-range order and are thus su-perconducting. In special cases the complete (T = 0) phase diagram can be obtained. The proposal to explain high-temperature superconductivity in the framework of strongly correlated electrons (Anderson 1987, Zhang and Rice 1988) has stimulated the search for purely electronic mechanisms of superconductivity. Unfortunately, only very few exact results are available. In this paper we will show that the so-called-pairing mechanism can be used to construct exact ground states for generalized Hubbard models in a wide range of interaction parameters. These-pairing states are known (Yang 1989) to exhibit oo-diagonal long-range order (ODLRO) (Yang 1962). Since ODLRO implies also the Meissner eeect and ux quantization (Sewell 1990, 1995, Nieh et.al. 1995) these states are superconducting.-pairing superconductivity is closely related to local-pair superconductivity which has been reviewed in (Micnas, Ranninger and Robaszkiewicz 1990). In the following we will be interested in generalized Hubbard models with Hamiltonian H = P hjli h jl , where hjli denotes nearest-neighbour sites on a d dimensional lattice and h jl = ?t X (c y j c l + c y l c j) +