Superconducting Field-Effect Devices

Abstract

Superconducting electronics has evolved primarily as a result of the discovery of Giaever tunneling and the Josephson effects. Originally both phenomena were dealt with in the framework of two superconductors separated by a thin insulating layer. However, the Josephson effect is a much more general phenomenon which reveals the macroscopic quantum character of the superconducting state. Hence, the Josephson effect is found in a large variety of weak link structures such as superconductors connected by a narrow, short metallic contact (called a microbridge), by a normal metal, or by an insulator. In all cases the main features of the Josephson effect are present. The structures differ only with respect to the details of conduction of quasiparticles. The current-voltage characteristic is determined by the Josephson effect acting in parallel to a device-specific quasiparticle current. For various applications the response of either the quasiparticle current or the Josephson current is used. Which device is useful for which application depends on the required impedance, on an often needed nonlinearity and on the maximum supercurrent.