Josephson current in a four terminal superconductor - exciton condensate - superconductor system

TL;DR

This paper studies how Josephson currents behave in a four-terminal superconductor-exciton condensate system, revealing a phase difference dependence and a novel four-particle Andreev process, with implications for topologically protected qubits.

Contribution

It demonstrates that Josephson currents depend only on phase differences in a superconductor-exciton condensate system and introduces a new four-particle Andreev process at the interface.

Findings

Josephson current depends only on phase difference between layers.

A novel four-particle Andreev process occurs at the interface.

System can implement supercurrent mirror for topological qubits.

Abstract

We investigate the transport properties of a bilayer exciton condensate that is contacted by four superconducting leads. We focus on the equilibrium regime and investigate how the Josephson currents induced in the bilayer by phase biases applied to the superconducting electrodes are affected by the presence of an exciton condensate in the bulk of the system. As long as the distance between the superconducting electrodes is much larger than the exciton coherence length, the Josephson current depends only on the difference between the phase biases in the two layers. This result holds true in both short- and long-junction limits. We relate it to a novel correlated four-particle Andreev process which occurs at the superconductor - exciton condensate interface. The system we investigate provides an implementation of the supercurrent mirror proposed by Kitaev as a viable way to realize topologically protected qubits.