D.C. Josephson transport by quartets and other Andreev resonances in superconducting bijunctions

TL;DR

This paper explores how three-terminal Josephson junctions, called bijunctions, exhibit unique Andreev resonances like quartets, driven by non-equilibrium Green's function theory, with recent experiments confirming these phenomena in diffusive aluminum-copper systems.

Contribution

It introduces a microscopic theory for quartet and Andreev resonance transport in bijunctions, supported by experimental observations.

Findings

Observation of quartet resonances in aluminum-copper bijunctions

Theoretical explanation via non-equilibrium Green's functions

Identification of multiple coherent Andreev reflections

Abstract

Bijunctions are three-terminal Josephson junctions where three superconductors are connected by a single weak link made of a metallic region or of quantum dots. Biasing two of the superconductors with commensurate voltages yields Andreev resonances that produce d.c. Josephson currents made of correlated Cooper pairs. For instance with applied voltages (0, V,-V), quartets formed by two entangled Cooper pairs are emitted by one reservoir towards the two others. Theory involving non-equilibrium Green's functions reveal the microsopic mechanism at play, e.g. multiple coherent Andreev reflections that provide an energy-conserving and fully coherent channel. Recent experiments on diffusive Aluminum-Copper bijunctions show transport anomalies that are interpreted in terms of quartet resonances.