Supercurrent mediated by helical edge modes in bilayer graphene

Kavli Affiliate: Srijit Goswami

| First 5 Authors: Prasanna Rout, Nikos Papadopoulos, Fernando PeƱaranda, Kenji Watanabe, Takashi Taniguchi

| Summary:

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.

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