Simple lattice model for d-type gap anisotropy for layered cuprates

Double electron exchange between Cu4s and O2p(sigma) orbitals is analyzed as mechanism which creates traditional cooper pairing in layered cuprates. The conductivity band is obtained in the oversimplified model which considers only hopping between O2p(sigma) orbitals, and the amplitude of the Cu4s - O2p(sigma) hybridization is accounted as perturbation. The proposed toy model possesses most of the distinguishable features of the experimental data: angle dependence of the superconducting gap, the shape of the Fermi surface, dispersion law for conductivity band and the electron spectrum of the superconducting phase. The influence of the Cu3d(x2-y2) orbital, electron doping and disorder for transition to s-type superconducting gap is briefly discussed.