Current-voltage characteristics of non equilibrium double-barrier superconducting tunnel junctions

An analysis is made of current-voltage characteristics of superconductor-insulatormetal-insulator-superconductor tunnel structures. The I-V-curves depend strongly on the competition between tunneling through the insulators and inelastic scattering in the metal. It is shown that if the metal is a superconductor with a low critical temperature, superconductivity will be induced above Tc through the transport current. This explains the observation of the superconducting gap of aluminium at T=4.2 K in recent experiments on Nb/AlOx/Al/AlOx/Nb tunnel junctions