扭曲双层石墨烯中的关联态
Correlated states in twisted double bilayer graphene
摘要：
电子-电子相互作用在石墨烯及相关体系中起着重要的作用，并且可以诱导奇异的量子态，特别是在具有小扭转角的堆叠双层中。对于双层石墨烯，其中两个层以“魔角”扭曲，平带和强多体效应导致相关绝缘态和超导性。与单层石墨烯相反，未扭曲的双层石墨烯的能带结构可以通过位移场进一步调谐，提供额外的自由度来控制当两个双层堆叠在彼此顶部时应该出现的平带。在这里，我们报告的发现和表征这种位移场可调电子相位在扭曲的双层石墨烯。我们观察到绝缘状态的半满导带中的一个中间范围的位移场。此外，在相关绝缘体的电阻间隙增加相对于面内磁场，我们发现，根据自旋塞曼效应的g因子为~2，表明自旋极化在半填充。这些结果建立了扭曲的双层石墨烯作为一个容易调谐的平台，探索量子多体状态。
英文摘要：
Electron-electron interactions play an important role in graphene and related systems and can induce exotic quantum states, especially in a stacked bilayer with a small twist angle. For bilayer graphene where the two layers are twisted by a "magic angle", flat band and strong many-body effects lead to correlated insulating states and superconductivity. In contrast to monolayer graphene, the band structure of untwisted bilayer graphene can be further tuned by a displacement field, providing an extra degree of freedom to control the flat band that should appear when two bilayers are stacked on top of each other. Here, we report the discovery and characterization of such displacement-field tunable electronic phases in twisted double bilayer graphene. We observe insulating states at a half-filled conduction band in an intermediate range of displacement fields. Furthermore, the resistance gap in the correlated insulator increases with respect to the in-plane magnetic fields and we find that the g factor according to spin Zeeman effect is ~2, indicating spin polarization at half filling. These results establish the twisted double bilayer graphene as an easily tunable platform for exploring quantum many-body states.
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