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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.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Bilayer graphene, topological phase, superconducting quantum interferometry

Date published: 2024-01-29

Publisher: Springer Science and Business Media LLC

Journal:

• Nature Communications (ISSN: 20411723) vol. 15 issue. 1 856

Funding:

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1038/s41467-024-44952-6

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Updated at: 2025-02-08 12:30:24 +0900

Published on MDR: 2025-02-08 12:30:24 +0900