Proximity effect tunneling into virtual bound state alloys

Abstract

The effects of a narrow virtual bound state formed by transition metal impurities dissolved in the normal layer of a superconducting proximity effect sandwich are studied. Using standard renormalization techniques, we obtain the changes in the transition temperatures and the jumps in the specific heat at Tc as a function of the thickness of the normal layer, of the widths of the virtual bound states, and of the impurity concentrations. It is seen that narrow virtual bound states lead to decreases in the transition temperatures, while broad virtual bound states do not. It is further seen that the narrow virtual bound state causes the reduced specific heat jump at Tc to deviate from the BCS behavior expected of the pure sandwich. © 1984 Plenum Publishing Corporation.