NEW 1/N EXPANSION METHOD FOR THE GENERALIZED HUBBARD-MODEL

We study the N-fold degenerate Hubbard model in the limits U --> infinity, N --> infinity, t --> 0 with Nt2 = const (U, on-site Coulomb correlation; t, nearest-neighbor hopping). In leading nontrivial order in 1/N one does not obtain simply a renormalized tight-binding band, which the slave-boson mean-field theory would predict, but a correlation-induced splitting of the lower Hubbard band. There exists an effective interaction between the electrons in different spin channels at nearest-neighbor sites in the case U --> infinity, in which the usual antiferromagnetic J congruent-to t2/U interaction vanishes.