Superconductive tunneling into Nb3Sn with barriers formed by RF oxidation

Thin film tunnel junctions were fabricated using rf oxidation of sputtered Nb
3
Sn films and subsequent evaporation of Pb. Very little control of junction impedance could be obtained from variation of the rf voltage or the partial pressure of oxygen. Small Josephson currents and high leakage in the quasi-particle characteristics were observed. Using an approximate proximity effect density-of-states model it appears that a damaged surface layer causes a reduced energy gap with a value somewhat dependent on the oxidation process. Two types of characteristics were observed and can be explained by the existence of two metallic phases in some of the films.