Proximity effect in Cu-Nb-Sn composites

Heat capacities have been measured in the presence of magnetic fields for Cu-Nb and Cu-Nb/sub 3/Sn in situ composites in order to determine the size of the superconducting pair potential which is induced in the normal Cu region as a function of magnetic field. For the Cu-Nb composites the induced pair potential is found to be about 0.35 MeV in zero field, in agreement with de Gennes boundary conditions. With the application of a magnetic field, the energy gap declines quickly and above about 17 mT the Cu behaves as a gapless superconductor. A family of life-time broadened density of states which gives the measured C/sub es/(Cu) is calculated based on the relation between the entropy S and density of states N(..omega..) derived for superconductors doped with paramagnetic impurities. Similar results are found in Cu-Nb/sub 3/Sn composites.