On the BCS theory of paramagnetic impurities in anisotropic superconductors

We develop a theory based on BCS theory which treats the effect of paramagnetic impurities in an anisotropic superconductor. It is found that in a separable model for the order parameter its anisotropy is expected to increase with increasing concentration of paramagnetic impurities. The critical temperature, the order parameter, and the quasiparticle density of states are computed numerically from our theoretical results. We find that there exists a regime which is superconducting by virtue of the fact that the paramagnetic impurities make the material highly anisotropic. In this regime the critical temperature can be reduced rapidly to zero by adding dilute concentrations of normal scattering impurities.Research supported by the Natural Sciences and Engineering Research Council of Canada.This paper is dedicated on the occasion of the 70th birthday of Prof. Dr. E. Ledinegg, head of the Institut für Theoretische Physik, Technische Universität, Graz, Austria.