Role of anisotropic impurity scattering in anisotropic superconductors

A theory of nonmagnetic impurities in an anisotropic superconductor including the effect of anisotropic (momentum-dependent) impurity scattering is given. It is shown that for a strongly anisotropic scattering the reduction of the pair-breaking effect of the impurities is large. For a significant overlap between the anisotropy functions of the scattering potential and that of the pair potential and for a large amount of anisotropic scattering rate in impurity potential the superconductivity becomes robust vis-a-vis impurity concentration. The implications of our result for YBCO high-temperature superconductor are discussed. The experimental data of electron irradiation-induced T-c suppression [Phys. Rev. B 50, 15 967 (1994)] are understood quantitatively and a good qualitative agreement with the ion (Ne+) damage and Pr substitution-induced T-c decrease data [Phys. Rev. B 50, 3266 (1994)] is obtained.