Compact SQUID realized in a double layer graphene heterostructure

TL;DR

This paper reports on a compact, tunable double-layer graphene SQUID with high transparency Josephson junctions, demonstrating potential for topological superconductivity via helical edge states in quantum Hall regimes.

Contribution

It introduces a fully tunable, small-scale double-layer graphene SQUID with high transparency junctions and explores its properties in quantum Hall conditions for topological applications.

Findings

Fully tunable by independent gate control.

Presence of high transparency superconducting modes.

Observation of conductance plateau indicating edge channels.

Abstract

Two-dimensional systems that host one-dimensional helical states are exciting from the perspective of scalable topological quantum computation when coupled with a superconductor. Graphene is particularly promising for its high electronic quality, versatility in van der Waals heterostructures and its electron and hole-like degenerate 0$th$ Landau level. Here, we study a compact double layer graphene SQUID (superconducting quantum interference device), where the superconducting loop is reduced to the superconducting contacts, connecting two parallel graphene Josephson junctions. Despite the small size of the SQUID, it is fully tunable by independent gate control of the Fermi energies in both layers. Furthermore, both Josephson junctions show a skewed current phase relationship, indicating the presence of superconducting modes with high transparency. In the quantum Hall regime we measure a well defined conductance plateau of 2$e^2/h$ an indicative of counter propagating edge channels in the two layers. Our work opens a way for engineering topological superconductivity by coupling helical edge states, from graphene's electron-hole degenerate 0$th$ Landau level via superconducting contacts.