Andreev processes in mesoscopic multi-terminal graphene Josephson junctions

TL;DR

This paper combines experimental and theoretical approaches to study multi-terminal graphene Josephson junctions, revealing that observed features can be explained by semi-classical circuit models, challenging interpretations of multiplet Cooper pairings.

Contribution

It demonstrates that differential resistance features in four-terminal graphene Josephson junctions can be modeled by a circuit network, questioning their use as definitive signatures of multiplet Cooper pairings.

Findings

Resonant features resemble multiplet Cooper pairings.

Circuit model predicts phase-dependent current behavior.

Differential resistance alone cannot confirm multiplet pairings.

Abstract

There is growing interest in using multi-terminal Josephson junctions (MTJJs) as a platform to artificially emulate topological phases and to investigate complex superconducting mechanisms such as quartet and multiplet Cooper pairings. Current experimental signatures in MTJJs have led to conflicting interpretations of the salient features. In this work, we report a collaborative experimental and theoretical investigation of graphene-based four-terminal Josephson junctions. We observe resonant features in the differential resistance maps that resemble those ascribed to multiplet Cooper pairings. To understand these features, we model our junctions using a circuit network of coupled two-terminal resistively and capacitively shunted junctions (RCSJs). Under appropriate bias current, the model predicts that a current flowing between two diagonal terminals in a four-terminal geometry may be represented as a sinusoidal function of a weighted sum of the superconducting phases. We show that starting from a semi-classical model with diffusive current-phase relations, the MTJJ effectively emulates a general form of the expected current-phase relation for multiplet Cooper pairings. Our study therefore suggests that differential resistance measurements alone are insufficient to conclusively distinguish resonant Andreev reflection processes from semi-classical circuit-network effects.