Kondo effect in superconductors: Depression of the transition temperature

Abstract

The influence of magnetic impurities on the transition temperature of superconducting alloys is investigated by means of the higher order parquet theory, which is essentially a self-consistent renormalization of the s-d interaction vertex and the quasi-fermion self-energy. The effective electron-electron interaction is evaluated beyond the logarithmic approximation, in terms of the renormalized spin-flip amplitude, which is responsible for the pair-breaking effect of the magnetic impurities. An expression for the maximal pair breaking, which is dependent on the spin and the superconducting coupling constant, is derived.