2-BAND MECHANISM OF SUPERCONDUCTIVITY IN THE 2-DIMENSIONAL HUBBARD-MODEL

In mufti-band systems having plural atomic sites in a unit cell, the on-site Coulomb interaction at each site brings about a process which transfers a pair of electrons between the bands. It is strong enough to make the system superconducting (SC) with a BCS-type pairing in a suitable situation of the band structure. We apply this idea to the two-dimensional Hubbard model. We assume the alternation of the transfer energy in one direction. It gives rise to a two-band situation. Features indicating SC are observed in exact-diagonalization calculations of a 4 x 4 cluster. The SC pair correlation functions increase step-wise in the region where the empty second band is in a slight touch with the Fermi level lying in the first band. Our scheme is considered to lead to the theory of Coulomb-origin mechanism of SC in the high T(C) oxides.