ANISOTROPY OF THE SUPERCONDUCTING GAP IN THE PRESENCE OF ELECTRON-PHONON AND COULOMB INTERACTIONS

d-wave and s-wave-type solutions of the BCS gap equations are studied numerically with account of long-range and short-range interaction wit h optical phonon and Coulomb repulsion. It is found that for realistic values of parameters the maximal value of the gap is determined mainl y by unscreened long-range interactions of charge carriers with long-w ave A(Ig)- and B-Ig- phonons. The type of the stable solution (d-wave or s-wave) essentially depends on the strength of the Coulomb repulsio n as well as on the strength of other short-range interaction potentia ls. The conclusion is drawn that in some members of cuprate supercondu ctors Cooper pairs may have d-wave symmetry while in others the symmet ry may be of aniso-tropic s-wave type.