Abstract
High-quality tunnel junctions have been fabricated on thin films of Nb-Sn (20-25 at.%) using oxidized -Si tunnel barriers and Pb counterelectrodes. These junctions have been used to measure changes in the gap, the transition temperature , and the tunneling density of states with composition in this important high- superconductor. With the use of the proximity-effect-modified data reduction scheme developed by Arnold and Wolf, values for and are obtained. As the Sn content approaches stoichiometry, the lowest-energy phonon branch in both increases in weight and shifts to lower energy. These two effects combine to produce the increases in as stoichiometry is approached, and at the same time can account for the observed increase in . The values of remain essentially constant as a function of composition, and hence show no evidence for an increased Coulomb interaction with increasing disorder as recently proposed by Anderson et al.
- Received 16 March 1984
DOI:https://doi.org/10.1103/PhysRevB.30.2590
©1984 American Physical Society