SUPERCONDUCTING PAIRING IN THE SINGLET BAND OF THE EMERY MODEL

The pairing due to electron-phonon and exchange interaction in the two -band Emery model is considered. The Emery model is reduced to an effe ctive singlet-triplet problem. The Eliashberg-equations are formulated in terms of Hubbard operators for the singlet band. The dependence of the critical temperature T-c on the number of holes n in the doped Cu O2 plane has been calculated. The electron-phonon coupling gives rise to s-wave pairing with a maximum in T-c at n congruent to 1.2. It corr espends to a maximum in the density of states for a doping value of n = 1.24. The anisotropic electron-electron coupling due to the exchange interaction produces extended s-wave pairing with a maximum at n cong ruent to 1.05 and d-wave pairing with a maximum at n congruent to 1.2.