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. Placing a single layer of tungsten diselenide in contact with twisted bilayer graphene enables superconductivity even for non-magic twist angles where insulating behavior is absent.

中文翻译：

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WSe2稳定的金属扭曲双层石墨烯的超导性

旋转错位接近 1.1 度的魔角扭曲双层石墨烯 (TBG) 具有孤立的扁平电子带，具有相关绝缘、超导、铁磁和拓扑相的丰富相图 1-6。相关绝缘体和超导性以前只在魔角 0.1 度以内的角度观察到，并且出现在相邻或重叠的电子密度范围内；然而，这些状态的起源以及它们之间的关系仍不清楚，因为它们对微观细节很敏感。除了扭转角和应变之外，TBG 相图对用于封装石墨烯片的绝缘六方氮化硼 (hBN)7,8 的排列4,6 和厚度的依赖性表明了微观介电环境的重要性。在这里，我们表明在 hBN 和 TBG 之间添加绝缘二硒化钨 (WSe2) 单层可以在比魔角小得多的扭转角下稳定超导性。对于 0.79 度的最小扭转角，尽管 TBG 在整个电子密度范围内都表现出金属行为，但仍观察到超导性。有限磁场测量进一步揭示了弱的反定位特征以及四重自旋谷对称性的破坏，这与 TBG 通过其接近 WSe2 引起的自旋轨道耦合一致。我们的结果限制了对 TBG 中超导性出现的理论解释，并开辟了在莫尔系统中设计量子相的途径。