Superconductivity in metallic twisted bilayer graphene stabilized by WSe2

Harpreet Singh Arora, Robert Polski, Yiran Zhang, Alex Thomson, Youngjoon Choi, Hyunjin Kim, Zhong Lin, Ilham Zaky Wilson, Xiaodong Xu, Jiun-Haw Chu, Kenji Watanabe, Takashi Taniguchi, Jason Alicea and Stevan Nadj-Perge ()
Additional contact information
Harpreet Singh Arora: California Institute of Technology
Robert Polski: California Institute of Technology
Yiran Zhang: California Institute of Technology
Alex Thomson: California Institute of Technology
Youngjoon Choi: California Institute of Technology
Hyunjin Kim: California Institute of Technology
Zhong Lin: University of Washington
Ilham Zaky Wilson: University of Washington
Xiaodong Xu: University of Washington
Jiun-Haw Chu: University of Washington
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Jason Alicea: California Institute of Technology
Stevan Nadj-Perge: California Institute of Technology

Nature, 2020, vol. 583, issue 7816, 379-384

Abstract: Abstract Magic-angle twisted bilayer graphene (TBG), with rotational misalignment close to 1.1 degrees, features isolated flat electronic bands that host a rich phase diagram of correlated insulating, superconducting, ferromagnetic and topological phases1–6. Correlated insulators and superconductivity have been previously observed only for angles within 0.1 degree of the magic angle and occur in adjacent or overlapping electron-density ranges; nevertheless, the origins of these states and the relation between them remain unclear, owing to their sensitivity to microscopic details. Beyond twist angle and strain, the dependence of the TBG phase diagram on the alignment4,6 and thickness of the insulating hexagonal boron nitride (hBN)7,8 used to encapsulate the graphene sheets indicates the importance of the microscopic dielectric environment. Here we show that adding an insulating tungsten diselenide (WSe2) monolayer between the hBN and the TBG stabilizes superconductivity at twist angles much smaller than the magic angle. For the smallest twist angle of 0.79 degrees, superconductivity is still observed despite the TBG exhibiting metallic behaviour across the whole range of electron densities. Finite-magnetic-field measurements further reveal weak antilocalization signatures as well as breaking of fourfold spin–valley symmetry, consistent with spin–orbit coupling induced in the TBG via its proximity to WSe2. Our results constrain theoretical explanations for the emergence of superconductivity in TBG and open up avenues towards engineering quantum phases in moiré systems.

Date: 2020
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DOI: 10.1038/s41586-020-2473-8

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