THE GINZBURG-LANDAU EXPANSION AND THE SLOPE OF THE UPPER CRITICAL-FIELD IN SUPERCONDUCTORS WITH ANISOTROPIC NORMAL-IMPURITY SCATTERING

We carry out the Ginzburg-Landau expansion for superconductors with an isotropic s and d pairing in the presence of anisotropic normal-impuri ty scattering, which enhances the stability of d pairing with respect to disordering. We find that the slope of the curve of the upper criti cal field, \dH(c2)/dT\(Tc), in superconductors with d pairing behaves nonlinearly as disorder grows: at low scattering anisotropy the slope rapidly decreases with increasing impurity concentration, then gradual ly but nonlinearly increases with concentration, reaches its maximum, and then rapidly decreases, vanishing at the critical impurity concent ration. In superconductors with anisotropic s pairing, \dH(c2)/dT/(Tc) always increases with impurity concentration, finally reaching the fa miliar asymptotic value characteristic of the isotropic case, irrespec tive of whether there is anisotropic impurity scattering. (C) 1997 Ame rican Institute of Physics. [S1063-7761(97)01412-1].