Tunable superconductivity in electron- and hole-doped Bernal bilayer graphene

Chushan Li, Fan Xu, Bohao Li, Jiayi Li, Guoan Li, Kenji Watanabe, Takashi Taniguchi, Bingbing Tong, Jie Shen, Li Lu, Jinfeng Jia, Fengcheng Wu (), Xiaoxue Liu () and Tingxin Li ()
Additional contact information
Chushan Li: Shanghai Jiao Tong University
Fan Xu: Shanghai Jiao Tong University
Bohao Li: Wuhan University
Jiayi Li: Shanghai Jiao Tong University
Guoan Li: Chinese Academy of Sciences
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Bingbing Tong: Chinese Academy of Sciences
Jie Shen: Chinese Academy of Sciences
Li Lu: Chinese Academy of Sciences
Jinfeng Jia: Shanghai Jiao Tong University
Fengcheng Wu: Wuhan University
Xiaoxue Liu: Shanghai Jiao Tong University
Tingxin Li: Shanghai Jiao Tong University

Nature, 2024, vol. 631, issue 8020, 300-306

Abstract: Abstract Graphene-based, high-quality, two-dimensional electronic systems have emerged as a highly tunable platform for studying superconductivity1–21. Specifically, superconductivity has been observed in both electron- and hole-doped twisted graphene moiré systems1–17, whereas in crystalline graphene systems, superconductivity has so far been observed only in hole-doped rhombohedral trilayer graphene (RTG)18 and hole-doped Bernal bilayer graphene (BBG)19–21. Recently, enhanced superconductivity has been demonstrated20,21 in BBG because of the proximity to a monolayer WSe2. Here we report the observation of superconductivity and a series of flavour-symmetry-breaking phases in electron- and hole-doped BBG/WSe2 devices by electrostatic doping. The strength of the observed superconductivity is tunable by applied vertical electric fields. The maximum Berezinskii–Kosterlitz−Thouless transition temperature for the electron- and hole-doped superconductivity is about 210 mK and 400 mK, respectively. Superconductivities emerge only when the applied electric fields drive the BBG electron or hole wavefunctions towards the WSe2 layer, underscoring the importance of the WSe2 layer in the observed superconductivity. The hole-doped superconductivity violates the Pauli paramagnetic limit, consistent with an Ising-like superconductor. By contrast, the electron-doped superconductivity obeys the Pauli limit, although the proximity-induced Ising spin–orbit coupling is also notable in the conduction band. Our findings highlight the rich physics associated with the conduction band in BBG, paving the way for further studies into the superconducting mechanisms of crystalline graphene and the development of superconductor devices based on BBG.

Date: 2024
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DOI: 10.1038/s41586-024-07584-w

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