Liu Xiaomeng, Chiu Cheng-Li, Lee Jong Yeon, Farahi Gelareh, Watanabe Kenji, Taniguchi Takashi, Vishwanath Ashvin, Yazdani Ali
Joesph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA.
Department of Physics, Harvard University, Cambridge, MA, USA.
Nat Commun. 2021 May 12;12(1):2732. doi: 10.1038/s41467-021-23031-0.
Moiré superlattices created by the twisted stacking of two-dimensional crystals can host electronic bands with flat energy dispersion in which enhanced interactions promote correlated electron states. The twisted double bilayer graphene (TDBG), where two Bernal bilayer graphene are stacked with a twist angle, is such a moiré system with tunable flat bands. Here, we use gate-tuned scanning tunneling spectroscopy to directly demonstrate the tunability of the band structure of TDBG with an electric field and to show spectroscopic signatures of electronic correlations and topology for its flat band. Our spectroscopic experiments are in agreement with a continuum model of TDBG band structure and reveal signatures of a correlated insulator gap at partial filling of its isolated flat band. The topological properties of this flat band are probed with the application of a magnetic field, which leads to valley polarization and the splitting of Chern bands with a large effective g-factor.
通过二维晶体的扭曲堆叠形成的莫尔超晶格可以容纳具有平坦能量色散的电子能带，其中增强的相互作用促进了关联电子态。扭曲双双层石墨烯（TDBG）是由两个伯纳尔双层石墨烯以一定扭曲角堆叠而成的，它就是这样一个具有可调平坦能带的莫尔系统。在这里，我们使用栅极调谐扫描隧道光谱直接证明了TDBG能带结构在电场作用下的可调性，并展示了其平坦能带的电子关联和拓扑结构的光谱特征。我们的光谱实验与TDBG能带结构的连续模型一致，并揭示了在其孤立平坦能带部分填充时关联绝缘体能隙的特征。通过施加磁场来探测这个平坦能带的拓扑性质，这会导致能谷极化以及具有大有效g因子的陈能带分裂。
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