Depression of superconducting critical temperature by impurities with Kondo effect

Depression of the superconducting critical temperature by impurities exhibiting the Kondo effect is investigated by taking account of an effective repulsion between electrons with anti-parallel spins resulting from the virtual polarization of impurities in singlet states. It is found that the critical temperature tends to zero at finite impurity concentrations, in contrast to the Muller-Hartmann-Zittartz theory. (author)