Superconducting electronic device with transistor-like properties

Particle and photon detectors based on both superconducting tunnel junctions and on superconducting transition edge sensors are becoming widely used, A superconducting transistor with large current gain and bandwidth that can operate in close proximity to the detectors could open up new possibilities. Recently the Naples-Oxford collaboration has fabricated and tested a three-terminal superconducting device with transistor-like properties at an operating temperature of 4.2 K. It consists of a stacked double tunnel junction structure where the intermediate film is a bilayer of superconducting Nb and an Al quasiparticle trap that can be either in the superconducting or in the normal metal state. Current amplification factors of more than 50 are observed at 4.2 K when the Al is in the normal state. The device also has power gain of more than 1000 and a high degree of unidirectionality. The results can be explained on the basis of the recently proposed QUAsiparticle TRApping TRANsistor, a device that should have wide applications in detection systems operating at low temperatures.