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arXiv · 2007.03735

Chern Insulators and Topological Flat-bands in Magic-angle Twisted Bilayer Graphene

Shuang Wu·Zhenyuan Zhang·K. Watanabe·T. Taniguchi·Eva Y. Andrei
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Abstract

Magic-angle twisted bilayer graphene (MA-TBG) exhibits intriguing quantum phase transitions triggered by enhanced electron-electron interactions when its flat-bands are partially filled. However, the phases themselves and their connection to the putative non-trivial topology of the flat bands are largely unexplored. Here we report transport measurements revealing a succession of doping-induced Lifshitz transitions that are accompanied by van Hove singularities (VHS) which facilitate the emergence of correlation-induced gaps and topologically non-trivial sub-bands. In the presence of a magnetic field, well quantized Hall plateaus at filling of 1, 2, 3 carriers per moir\'e-cell reveal the sub-band topology and signal the emergence of Chern insulators with Chern-numbers, ! = !, !, !, respectively. Surprisingly, for magnetic fields exceeding 5T we observe a VHS at a filling of 3.5, suggesting the possibility of a fractional Chern insulator. This VHS is accompanied by a crossover from low-temperature metallic, to high-temperature insulating behavior, characteristic of entropically driven Pomeranchuk-like transitions,

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Shuang Wu, Zhenyuan Zhang, K. Watanabe, T. Taniguchi, Eva Y. Andrei. 2020-07-07. Chern Insulators and Topological Flat-bands in Magic-angle Twisted Bilayer Graphene. https://doi.org/10.1038/s41563-020-00911-2

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