电子掺杂与空穴掺杂Bernal双层石墨烯中的可调超导性
Tunable superconductivity in electron- and hole-doped Bernal bilayer graphene
AI总结：
本研究在电子和空穴掺杂的BBG/WSe₂器件中观测到可调超导性与味对称破缺相，明确了WSe₂层的关键作用，揭示了两类掺杂超导的不同泡利极限行为，为晶体石墨烯超导研究与器件开发提供了新方向。
摘要：
基于石墨烯的高质量二维电子系统已成为研究超导性的高度可调平台。具体而言，超导性已在电子掺杂和空穴掺杂的转角石墨烯莫尔系统中被观测到，而在晶体石墨烯系统中，迄今为止超导性仅在空穴掺杂的菱方三层石墨烯和空穴掺杂的Bernal双层石墨烯（BBG）中被观测到。近期，由于与单层WSe₂邻近，BBG中已被证实存在增强的超导性。\n在此，我们报道了通过静电掺杂，在电子掺杂和空穴掺杂的BBG/WSe₂器件中均观测到超导性以及一系列味对称破缺相。所观测到的超导性强度可通过施加的垂直电场进行调控。电子掺杂和空穴掺杂超导的最高Berezinskii-Kosterlitz-Thouless（BKT）转变温度分别约为210 mK和400 mK。仅当施加的电场将BBG的电子或空穴波函数推向WSe₂层时，超导性才会出现，这凸显了WSe₂层在所观测超导性中的重要性。我们发现，空穴掺杂的超导性违反泡利顺磁极限，与类伊辛超导体的特征一致。相比之下，尽管邻近效应诱导的伊辛自旋轨道耦合在导带中也较为显著，但电子掺杂的超导性仍遵循泡利极限。我们的研究结果凸显了BBG导带相关的丰富物理现象，为进一步研究晶体石墨烯的超导机制以及开发基于BBG的新型超导器件铺平了道路。
英文摘要：
Graphene-based, high quality two-dimensional electronic systems have emerged as a highly tunable platform for studying superconductivity. Specifically, superconductivity has been observed in both electron-doped and hole-doped twisted graphene moire systems, whereas in crystalline graphene systems, superconductivity has so far only been observed in hole-doped rhombohedral trilayer and hole-doped Bernal bilayer graphene (BBG). Recently, enhanced superconductivity has been demonstrated in BBG due to the proximity with a monolayer WSe2. Here, we report the observation of superconductivity and a series of flavor-symmetry-breaking phases in both electron- and hole-doped BBG/WSe2 device by electrostatic doping. The strength of the observed superconductivity is tunable by applied vertical electric fields. The maximum Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for the electron- and hole-doped superconductivity is about 210 mK and 400 mK, respectively. Superconductivities emerge only when applied electric fields drive BBG electron or hole wavefunctions toward the WSe2 layer, underscoring the importance of the WSe2 layer in the observed superconductivity. We find the hole-doped superconductivity violates the Pauli paramagnetic limit, consistent with an Ising-like superconductor. In contrast, the electron-doped superconductivity obeys the Pauli limit, even though 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 novel superconductor devices based on BBG.
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