Impurities with internal degrees of freedom in superconductors

Abstract

In this paper we investigate the properties of an electron gas interacting with a system of nonmagnetic impurities having internal degrees of freedom which allow the electrons to be scattered inelastically. We determine the modifications of the Green's functions in the normal and superconducting state due to this inelastic scattering, and calculate the change of the superconducting transition temperature, of the order parameter, and of the density of states. In our model the transition temperature and the order parameter are shown to increase, and the density of states is shown to change its functional behavior drastically. The elastic part of the scattering affects neither the transition temperature, nor the order parameter, nor the density of states.