Effect of normal impurities on anisotropic superconductors with variable density of states

We develop a generalized BCS theory of impure superconductors with an anisotropic electron-electron interaction represented by the factorizable model introduced by Markowitz and Kadanoff, and a variable electronic density of statesN(), assumed to peak at the Fermi energy, which is modeled by a Lorentzian superimposed on a uniform background. As the impurity scattering is increased, the enhancement ofT_c by both the anisotropy and the peak inN() is washed out. The reduction is investigated for different values of the anisotropy and different peak heights and widths. It is concluded that the effects of anisotropy and the peak are reduced together in such a way that any effect due to anisotropy is not easily distinguishable from that due to the peak.Research supported by the Natural Sciences and Engineering Research Council of Canada and the McMaster University Science and Engineering Research Board.