Investigations of the proximity effect by electron tunneling

We have investigated the proximity effect in the Ag-Pb, Cu-Pb, and Sn-Pb systems by electron tunneling. A well-defined gap structure is induced in the normal metals by contact with the superconductor and, in tin below its transition temperature, the gap is augmented by the proximity of the lead. The results are in reasonable agreement with a theory of McMillan's and indicate electron transmission coefficients at the Ag-Pb, Cu-Pb, and Sn-Pb interfaces of about 0.1, 0.1, and 0.5, respectively. © 1969 The American Physical Society.