Functional derivative ofT c with ?2(?)F(?) for weak coupling anisotropic superconductors

Abstract

Approximate analytic calculations of the functional derivative of T/sub c/ with respect to ..cap alpha../sup 2/(..omega..)F(..omega..) for anisotropic superconductors are presented, with the primary purpose of identifying the determining material parameters. The ''square-well model'' for the phonon-mediated electron-electron interaction, the weak coupling limit (..omega../sub c//2..pi..T/sub c/>>1), an separable anisotropy are used. The general behavior of deltaT/sub c//delta..cap alpha../sup 2/(..omega..)F(..omega..) is the same as that found in numerical calculations for the case of small anisotropy, /(lambda-..mu..*)<<1; the regime of ..mu..*approx. =lambda is also discussed.