Critical temperatures in the three-band extended Hubbard model

Wt investigate the three-band extended Hubbard model for the CuO2 planes of high-temperature superconductors. We consider the limit of U = infinity on Cu atoms and we include the nearest-neighbor Coulomb repulsion between holes on 2p(x,y) orbitals of oxygen and holes on 3d(x2-y2) or 3d(3z2-r2) orbitals of copper (V-x and V-z respectively, with V-x > V-z). This leads to the effective negative nearest-neighbor Coulomb inter action. Numerical analysis of this model reveals the possibility of s-wave and d-wave: superconductivity arising from the difference DeltaV = V-z - V-x. It was shown that the s-wave superconductivity is driven by DeltaV and is opposed by the Coulomb repulsion on oxygen, U-p. while the d-wave superconductivity is influenced only by the driving force, DeltaV This fact would enable existence of the d-wave superconductivity in many high temperature superconducting materials.