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SYWH: Symposium Physics of van der Waals 2D heterostructures

SYWH 1: Symposium: Physics of van der Waals 2D heterostructures

SYWH 1.5: Hauptvortrag

Donnerstag, 30. September 2021, 15:45–16:15, Audimax 2

Chern Insulators, van Hove singularities and Topological Flat-bands in Magic-angle Twisted Bilayer Graphene* — •Eva Andrei, Shuang Wu, and Zhenyuan Zhang — Dept. of Physics, Rutgers University, Piscatay NJ 08904, USA

Magic-angle twisted bilayer graphene exhibits intriguing quantum phase transitions triggered by enhanced electron-electron interactions when its flat-bands are partially filled. These phases and their experimental manifestations provide clues to the underlying non-trivial band topology. In particular, transport measurements revealed a succession of doping-induced phase transitions at integer moiré fillings. We have shown that these transitions 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 moiré-cell reveal the sub-band topology and signal the emergence of Chern insulators. Surprisingly, for magnetic fields exceeding 5T we observe a VHS at a filling of 3.5, suggesting the emergence of a fractional Chern insulator.

Shuang Wu, Zhenyuan Zhang, K. Watanabe, T. Taniguchi, Eva Y. Andrei, Nature Materials, 20 (2021) p488