Self-consistent theory of pairbreaking in kondo superconductors

A theory is presented for the calculation of equilibrium properties of superconductors containing magnetic impuritiesof finite concentration. The theory is based on the Nagaoka-Suhl approach to thes — d model and treats finite impurity concentrations within a self-consistentT-matrix-approximation. An integral equation is derived for the pairbreaking parameter which describes de-pairing of Cooper pairs by spin flip scattering. Numerical solutions of this equation are used to compute the phase diagram in the temperature-concentration-plane and the transition-temperature-dependence of the upper critical field. These calculations are in good agreement with experimental data on LaCeAl₂-samples. In addition, the recent discovery of three normal superconducting transitions in LaCeY is discussed quantitatively.Work performed within the research program of the Sonderforschungsbereich 125 Aachen/Jülich/Köln