Non-equilibrium in Josephson junctions: Possible transistor-like applications

Interest in superconducting transistors is due to some potential benefits o f these devices, such as the possibility to have large current gain and ban dwidth at low temperatures. In this work we present experimental results co ncerning with a new superconducting 3-terminal device showing true transist or-lice properties at T=4.2K. It is a stacked double tunnel junction struct ure where the intermediate film is a bilayer of superconducting Nb with an Al quasiparticle trap which can be either in the superconducting or in the normal metal state. Current amplification factors of up to 2.0 are observed at a temperature of 4.2 K when the Al is superconducting. When the Al is i n the normal State, large current gains of more than 50 are observed The op eration is highly directional, i.e. practically no effect is observed when the roles of the injector and detector junctions are reversed. The results are explained according to the recently proposed QUAsiparticle TRApping TRA Nnsistor model.