T<inf>c</inf>of anisotropic superconductors containing non-magnetic resonant states

Abstract

The effects of resonant scattering by non-magnetic Anderson impurities on the transition temperatures of anistropic superconductors are investigated within the framework of the weak coupling BCS theory and the strong coupling Migdal-Eliashberg theory. The separable anisotropic interaction V kk′ = [1 + a k (Ω)]g[1 + a k′ (Ω′)] - V c is used used in the calculations based on the BCS formalism while the separable spectral function α 2 F kk′ (ω) = [1 + a k (Ω)]α 2 F(ω)[1 + a k′ (Ω′)] is used in the calculations based on the square well model λ θθ of the Migdal-Eliashberg formalism. It is shown that the two formalisms lead to expressions for T c which are very similar. © 1986.