S-WAVE AND D-WAVE SYMMETRIES OF THE SOLUTIONS OF THE ELIASHBERG EQUATIONS

We examine the different possible symmetries of the superconducting ga p obtained by solving the Eliashberg equations. We consider an electro n-phonon interaction in a strong coupling scenario. The Coulomb pseudo potential plays the crucial role of providing the, repulsion needed to favour the d-wave symmetry. But the key parameter that allows very an isotropic solutions even with very strong coupling is the small angula r range of the interaction due to predominantly electron-phonon forwar d scattering that is found in the high-T-c superconductors. We find bo th s- and d-wave solutions whose stability depends mainly on the angul ar range of the interaction.