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Superconductivity in a two-band Hubbard model.

As a model for high-{Tc} superconductors, a two-band Hubbard model is proposed. When the Coulomb interactions are introduced between the {alpha} and {beta} orbitals, an effective attraction of carriers in the {beta} (doped) band is shown to arise in an appropriate condition. The quantum Monte Carlo method is used to confirm the occurrence of Cooper pairing in finite two-band Hubbard systems. The attraction, which also appears in the density-density correlation, enhances the on-site singlet Cooper pair-pair correlation in the {beta} band and suppresses the antiferromagnetic spin-spin correlation in the {alpha} band. The criterion for the pairing and the nature of the pairing are discussed. Thus we provide a mechanism of superconductivity specific to strongly correlated two-band systems.