Tunneling Between Superconductors

Josephson's calculations showed that for two superconductors separated by an oxide there may exist an osciliating supercurrent of frequency 2e V/h (V is applied voltage) and a possible d-c supercurrent at zero voltage. The calculations are reproduced by the method of the thermodynamic Green's function that allows generalization to superconductors with strong electron-phonon coupling. A simple prediction for the temperature dependence of the d-c supercurrent is shown to follow from the theory. (D.C.W.)