Type II Superconductors Containing Magnetic Impurities

A theoretical study is made on the equilibrium as well as on the dynamical properties of type II superconductors containing magnetic impurities. The Kondo effect associated with the impurity spins is taken into account within the pole approximation, which has been used previously by Muller-Hartmann and Zittarz in their calculation of the superconducting transition temperature. In this approximation we have still the additive law of the different pair-breaking mechanisms for the transition temperature; the sum of the pair-breaking parameters due to magnetic impurities and due to magnetic fields is a universal function of the temperature. Since the pair-breaking parameter arising from magnetic impurities has the maximum at T congruent to T-K, the upper critical field H-c2(T) reflects the Kondo effect in the system. The kappa(2)(T) parameter, which describes the magnetization as well as the flux-flow resistivity of the vortex state, is obtained. When T-K/T-c0 > 1, kappa(2)(T) increases as the temperature decreases, but when T-K/T-c0 < 1, kappa(2)(T) first increases as the temperature decreases, then passing a maximum and decreasing at low temperatures, which is in sharp contrast to that obtained previously where the impurity scattering was treated with the Born approximation (i.e., the Kondo effect was completely neglected.) A brief discussion of the density of states in the gapless region is also given, which reflects the Kondo effect in an interesting way.