Binding of holes in one-band models of oxide superconductors

We have performed exact-diagonalization studies of the ground state of the one-band Hubbard model and the related strong-coupling Hamiltonian near half-filling. A tendency towards superconductivity, indicated by a negative ``binding energy,'' is found to be greater for the strong-coupling Hamiltonian. We find that two holes are attracted to each other for parameter values where the binding energy is negative. The symmetry of the two-hole bound state of the strong-coupling Hamiltonian is predominantly , in agreement with other calculations.