Magic-angle Twisted Bilayer Systems with Quadratic-Band-Touching: Exactly Flat Bands with High-Chern Number

Twisted bilayer morie system, mainly the twisted bilayer graphene and twisted transition-metal-dichalcogenide, have provided a tunable platform to study the strong-correlation effect in flat band materials. Here we propose a new twisted bilayer of 2D systems that feature quadratic-band-touching (QBT) points, we find that exactly flat bands can emerge at the magic angles and each of them has a high Chern number C=±2 which was not realized before. We further explain the origin of the exactly flat band and derive the first magic angle. Finally, we study the Coulomb interactions effect at the magic angle and obtain the ground state at 1/4 filling which supports the quantum anomalous Hall effect quantized Hall conductivity 2e²/hc.

Reference: arXiv:2111.12107