Investigation of Supercurrent in the Quantum Hall Regime in Graphene Josephson Junctions

TL;DR

This paper investigates the mechanisms behind supercurrent in graphene Josephson junctions within the quantum Hall regime, focusing on how device geometry influences supercurrent flow and identifying likely underlying processes.

Contribution

It provides experimental insights into supercurrent mechanisms in graphene QH regimes, especially distinguishing between edge conduction and hybrid electron-hole modes.

Findings

Supercurrent is suppressed in extended junctions.

Edge length influences supercurrent presence.

Hybrid electron-hole modes likely mediate supercurrent.

Abstract

In this study, we examine multiple encapsulated graphene Josephson junctions to determine which mechanisms may be responsible for the supercurrent observed in the quantum Hall (QH) regime. Rectangular junctions with various widths and lengths were studied to identify which parameters affect the occurrence of QH supercurrent. We also studied additional samples where the graphene region is extended beyond the contacts on one side, making that edge of the mesa significantly longer than the opposite edge. This is done in order to distinguish two potential mechanisms: a) supercurrents independently flowing along both non-contacted edges of graphene mesa, and b) opposite sides of the mesa being coupled by hybrid electron-hole modes flowing along the superconductor/graphene boundary. The supercurrent appears suppressed in extended junctions, suggesting the latter mechanism.