SUPERCONDUCTIVITY IN A 2-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 and orbitals, an effective attraction of carriers in the (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 band and suppresses the antiferromagnetic spin-spin correlation in the 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. © 1990 The American Physical Society.