Flux transistor made from a single-layer niobium thin-film superconducting quantum interference device

A micrometre-size Josephson vortex flow transistor is demonstrated experimentally. The drain-source of this device is the output of a single-layer Nb superconducting quantum interference device (SQUID) with a nanometre-size hole, forming a nanoSQUID. The device input is a Nb strip, which is closely coupled to the nanoSQUID. The change of the input current induces a change in the magnetic flux coupling to the nanoSQUID, and hence modulates the current-voltage characteristics of the nanoSQUID. The current gain and transresistance of the device were investigated by evaluating the mutual coupling and the dynamic resistance of the nanoSQUID. A current gain of 0.3 and a transresistance >1 Ω were achieved