Supercurrent mediated by helical edge modes in bilayer graphene

TL;DR

This paper demonstrates the coupling of superconductivity to topological helical edge states in bilayer graphene, revealing an even-odd interference pattern that confirms the topological nature of the inverted gap phase.

Contribution

It provides experimental evidence of supercurrent coupling to helical edge modes in bilayer graphene, highlighting the topological origin of the observed effects.

Findings

Observation of an even-odd effect in Fraunhofer patterns

Suppression of critical current in the inverted gap phase

Confirmation of topological helical edge states

Abstract

Bilayer graphene encapsulated in tungsten diselenide can host a weak topological phase with pairs of helical edge states. The electrical tunability of this phase makes it an ideal platform to investigate unique topological effects at zero magnetic field, such as topological superconductivity. Here we couple the helical edges of such a heterostructure to a superconductor. The inversion of the bulk gap accompanied by helical states near zero displacement field leads to the suppression of the critical current in a Josephson geometry. Using superconducting quantum interferometry we observe an even-odd effect in the Fraunhofer interference pattern within the inverted gap phase. We show theoretically that this effect is a direct consequence of the emergence of helical modes that connect the two edges of the sample. The absence of such an effect at high displacement field, as well as in bare bilayer graphene junctions, confirms this interpretation and demonstrates the topological nature of the inverted gap. Our results demonstrate the coupling of superconductivity to zero-field topological states in graphene.