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Supercurrent mediated by helical edge modes in bilayer graphene

P. Rout,N. Papadopoulos,F. Peñaranda,Kenji Watanabe,T. Taniguchi,E. Prada,P. San-Jose,S. Goswami

Published 2023 in Nature Communications

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, supports this interpretation and demonstrates the topological nature of the inverted gap. P. Rout et al. study Josephson junctions where the weak link is WSe2-encapsulated bilayer graphene, which features helical edge modes. They argue that the supercurrent channels along opposite edges of the weak link are coupled by a circulating helical mode.

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