On a weak-coupling theory of superconducting magnetic alloys

Abstract

The interaction of electrons with magnetic impurities in superconducting magnetic alloys is calculated to second order in the spin exchange coupling. Its effects on the transition temperature, the order parameter, the density of states, and the conductance are studied. The results are as follows. (1) The variation of the transition temperature with impurity concentration is the same as in the Abrikosov-Gor'kov theory; that of the order parameter is similar. (2) The density of states is finite at all nonzero impurity concentrations. Superconductivity with magnetic impurities is always gapless. (3) There are far more states about the Fermi level than in the Abrikosov-Gor'kov theory. At an impurity concentration equal to two-thirds its critical value, the density of states at the Fermi level surpasses one-half the normal value. The conductance curve loses all semblance of an energy gap.