Superconducting device with transistor-like properties including large current amplification

We have fabricated and studied a stacked superconducting double tunnel junc tion device with transistor-like properties. The intermediate electrode is a bilayer consisting of a Nb film together with an Al film that acts as a q uasiparticle trap. Large current gains of more than 50 are observed at 4.2 K when the Al layer is normal. The operation is highly directional. Results are explained on the basis of trapping of quasiparticles from a supercondu ctor into a normal metal, together with a conversion of relaxation energy i nto electronic excitations. Similar devices should have wide applications i n low-temperature measurement and detection systems. (C) 2000 American Inst itute of Physics. [S0003-6951(00)03628-7].