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Magic-angle twisted bilayer graphene (MATBG) can host an intriguing variety of gate-tunable correlated states, including su- perconducting and correlated-insulator states. Junction-based superconducting devices, such as Josephson junctions and SQUIDs, have been introduced recently and enable the exploration of the charge, spin, and orbit nature of su- perconductivity and the coherence of moir ́e electrons in MATBG. However, complementary fundamental coherence effects — in particular, the Little–Parks effect in superconducting and the Aharonov–Bohm effect in normal-conducting ring — remained to be observed. Here, we report the observation of both these phenomena in a sin- gle gate-defined ring device where we can embed superconducting or normal-conducting rings in a correlated or band insulator. We directly observe the Little–Parks effect in the superconducting phase diagram as a function of density and magnetic field, confirming the effective charge of 2e. By measuring the Aharonov–Bohm effect, we find that in our device, the coherence length of normal-conducting moir ́e electrons exceeds a few microns at 50 mK. Surprisingly, we also identify a regime characterized by h/e-periodic oscilla- tions but with superconductor-like nonlinear transport. Taken together, these experiments establish a novel device platform in MATBG, and more generally in tunable 2D materials, to un- ravel the nature of superconductivity and other correlated quantum states in these materials.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Magic-angle twisted bilayer graphene, superconducting states, Little–Parks effect

Date published: 2024-01-09

Publisher: Springer Science and Business Media LLC

Journal:

• Nature Communications (ISSN: 20411723) vol. 15 issue. 1 390

Funding:

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

MDR DOI:

First published URL: https://doi.org/10.1038/s41467-023-44671-4

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Updated at: 2025-02-15 12:30:51 +0900

Published on MDR: 2025-02-15 12:30:51 +0900