Superconductivity in metallic twisted bilayer graphene stabilized by WSe2
Superconductivity in metallic twisted bilayer graphene stabilized by WSe2
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DOI：
10.1038/s41586-020-2473-8
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发表时间：
2020-07-16
期刊：
影响因子：
64.8
通讯作者：
Nadj-Perge, Stevan
中科院分区：
文献类型：
--
作者：
Arora, Harpreet Singh;Polski, Robert;Nadj-Perge, Stevan
磁角扭曲双层石墨烯（TBG），旋转偏差接近1.1度，具有隔离的平面电子带，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的0.1度范围内观察到，并且发生在相邻或重叠的电子密度范围内；然而，由于它们对微观细节的敏感性，这些状态的起源和它们之间的关系仍然不清楚。除了扭转角和应变外，用于封装石墨烯片的绝缘六方氮化硼（hBN）（7,8）的取向（4,6）和厚度对TBG相图的依赖性表明微观介电环境的重要性。在hBN和TBG之间添加绝缘的二硒化钨（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表现出金属行为，但仍然观察到超导性。有限磁场测量进一步揭示了弱的反局域特征以及四重自旋谷对称性的破坏，这与TBG中由于靠近WSe2而引起的自旋轨道耦合一致。我们的结果限制了TBG中超导性出现的理论解释，并为云纹系统中的工程量子相开辟了道路。将单层二硒化钨与扭曲的双层石墨烯接触，即使在没有绝缘行为的非神奇扭曲角下也能实现超导性。
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 phases(1-6). 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 alignment(4,6)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 moire 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.