UNIVERSAL REDUCTION OF TC IN STRONG-COUPLING SUPERCONDUCTORS BY A SMALL CONCENTRATION OF MAGNETIC-IMPURITIES

The first exact calculation of Tc in the presence of a dilute concentration c of uncorrelated magnetic impurities is presented. The shape of Tc(c) is universal, Tc(c)/Tc0 =h[cf(0)/N(0)Tc0,TK/Tc0]. The detailed shape of Tc(c)/Tc0 is qualitatively and quantitatively different from that found by previous approximate theories. Tc(c) depends strongly upon the electron-phonon coupling 0. There is no indication of a low-temperature tail of positive curvature for TK/Tc0<1, or the associated third transition temperature Tc3, both predicted by Müller-Hartmann and Zittartz. My results agree well with experimental data. © 1990 The American Physical Society.