2005 Volume 60 Issue 2 Pages 95-101
Both Kondo effect and superconductivity are remarkable phenomena which conduction electrons in metals show at low temperatures. In metals containing magnetic impurities, the antiferromagnetic coupling between the impurity spin and the conduction electrons leads to a formation of spin singlet due to the Kondo effect, whereas in superconductors conduction electrons form Cooper pairs (spin singlet in most cases). Therefore superconductivity competes with the Kondo effect. The competition can be described with the ratio of the Kondo temperature TK to the superconducting transition temperature Tc. In the present article the relation between the Kondo effect and superconductivity is reviewed by taking up two problems: (1) electronic states of magnetic impurities in superconductors and (2) the influence of the Kondo effect on Josephson coupling beween two superconductors, which are connected via quantum dot.