Andreev scattering and the Kondo effect

The properties of an infinite-U Anderson impurity coupled to both normal and superconducting metals is studied using a generalization of the noncrossing approximation which incorporates multiple Andreev reflection. Both the cases of a quantum dot and a point contact containing an impurity are considered. We find that the magnitude of the Kondo resonance is altered, and that structure develops at energies corresponding to the superconducting gap. This leads to observable changes in the zero-bias conductance. We also find that magnetic and nonmagnetic Kondo effects respond in opposite manners to Andreev reflection.