Electron Tunneling into Superconducting Mercury Films at Temperatures below 0.4°K

The tunneling characteristics of aluminum-aluminum-oxide-mercury junctions have been measured at temperatures down to 0.35^∘{}K. Structure has been observed in addition to that seen in an earlier higher-temperature experiment. The data have been analyzed by a computer program written by McMillan and based on the strong-coupling theory. The tunneling density of states, the effective phonon spectrum, the complex energy-gap function, and the electron renormalization function have been determined for mercury. The effective electron-phonon interaction constant and the first and second moments of the effective phonon spectrum have also been determined.