Resonant superexchange in a three-dimensional anisotropic Hubbard model

This paper proposes the resonant superexchange electronic mechanism to explain superconductivity both in layered copper oxides and in Ba1-xKxBiO3 as well. Due to the fact that perfect two dimensional (2-D) systems present fluctuations which destroy superconductivity, the authors have applied the above mechanism to anisotropic systems like La2-xSrxCuO4. This paper concentrates on the derivation of the analytic expression of an effective interaction in three dimensions (3-D). As a natural difference with the isotropic case, the authors obtain two effective superexchange contributions which have a common resonance in energy. Both the 3-D isotropic and the e-D results are obtained as particular cases