Transistors based on proximity effect control of the critical current of a superconductor

The critical current of a bilayer consisting of a thin superconductor in contact with a normal conductor depends on the thickness of the normal layer due to the proximity effect. Using one electrode of a semiconductor pn junction as the normal material, it is possible to vary the normal layer thickness by applying a voltage to the pn junction. The author discusses the feasibility of transistors based on such structures. He concludes that there is no fundamental impediment to operating a transistor based on proximity effect control of a superconductor. However, the proposed device requires that both superconductor and semiconductor layers be no thicker than roughly a coherence length. The large mismatch at the superconductor-semiconductor interface reduces the size of the proximity effect, possibly making the desired effect too small to be useful. It is difficult to construct a nonlatching device, or one with voltage gain. Thus, the proposed device has major drawbacks which prevent it from being considered as more than a scientific curiosity.<>