Evidence for chiral supercurrent in quantum Hall Josephson junctions

Hadrien Vignaud, David Perconte, Wenmin Yang, Bilal Kousar, Edouard Wagner, Frédéric Gay, Kenji Watanabe, Takashi Taniguchi, Hervé Courtois, Zheng Han, Hermann Sellier and Benjamin Sacépé ()
Additional contact information
Hadrien Vignaud: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel
David Perconte: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel
Wenmin Yang: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel
Bilal Kousar: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel
Edouard Wagner: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel
Frédéric Gay: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Hervé Courtois: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel
Zheng Han: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel
Hermann Sellier: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel
Benjamin Sacépé: Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel

Nature, 2023, vol. 624, issue 7992, 545-550

Abstract: Abstract Hybridizing superconductivity with the quantum Hall (QH) effect has notable potential for designing circuits capable of inducing and manipulating non-Abelian states for topological quantum computation1–3. However, despite recent experimental progress towards this hybridization4–15, concrete evidence for a chiral QH Josephson junction16—the elemental building block for coherent superconducting QH circuits—is still lacking. Its expected signature is an unusual chiral supercurrent flowing in QH edge channels, which oscillates with a specific 2ϕ0 magnetic flux periodicity16–19 (ϕ0 = h/2e is the superconducting flux quantum, where h is the Planck constant and e is the electron charge). Here we show that ultra-narrow Josephson junctions defined in encapsulated graphene nanoribbons exhibit a chiral supercurrent, visible up to 8 T and carried by the spin-degenerate edge channel of the QH plateau of resistance h/2e2 ≈ 12.9 kΩ. We observe reproducible 2ϕ0-periodic oscillations of the supercurrent, which emerge at a constant filling factor when the area of the loop formed by the QH edge channel is constant, within a magnetic-length correction that we resolve in the data. Furthermore, by varying the junction geometry, we show that reducing the superconductor/normal interface length is crucial in obtaining a measurable supercurrent on QH plateaus, in agreement with theories predicting dephasing along the superconducting interface19–22. Our findings are important for the exploration of correlated and fractional QH-based superconducting devices that host non-Abelian Majorana and parafermion zero modes23–32.

Date: 2023
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DOI: 10.1038/s41586-023-06764-4

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