Observation of a controllable PI-junction in a 3-terminal Josephson device

TL;DR

This paper reports the experimental observation and theoretical explanation of supercurrent reversal in a 3-terminal Josephson device, demonstrating controllable phase states driven by nonequilibrium electron distributions.

Contribution

It introduces a 3-terminal Josephson device exhibiting controllable supercurrent reversal, extending previous 4-terminal findings with a simpler configuration.

Findings

Supercurrent reversal observed in 3-terminal device.

Theoretical explanation based on nonequilibrium physics.

Critical current amplitude comparable to 4-terminal devices.

Abstract

Recently Baselmans et al. [Nature, 397, 43 (1999)] showed that the direction of the supercurrent in a superconductor/normal/superconductor Josephson junction can be reversed by applying, perpendicularly to the supercurrent, a sufficiently large control current between two normal reservoirs. The novel behavior of their 4-terminal device (called a controllable PI-junction) arises from the nonequilibrium electron energy distribution established in the normal wire between the two superconductors. We have observed a similar supercurrent reversal in a 3-terminal device, where the control current passes from a single normal reservoir into the two superconductors. We show theoretically that this behavior, although intuitively less obvious, arises from the same nonequilibrium physics present in the 4-terminal device. Moreover, we argue that the amplitude of the PI-state critical current should be at least as large in the 3-terminal device as in a comparable 4-terminal device.