Magic-angle twisted bilayer systems with quadratic band touching: Exactly flat bands with high Chern number

Studies of twisted moire systems have been mainly focused on two-dimensional (2D) materials such as graphene with Dirac points and transition-metal dichalcogenides so far. Here we propose a twisted bilayer of 2D systems which feature stable quadratic-band-touching points and find exotic physics different from previously studied twisted moire systems. Specifically, we show that exactly flat bands can emerge at magic angles and, more interestingly, each flat band exhibits a high Chern number (C = +/- 2). We further consider the effect of Coulomb interactions in such magic-angle twisted systems and find that the ground state supports the quantum anomalous Hall effect with quantized Hall conductivity 2e2hc at certain filling. Furthermore, the possible physical realization of such twisted bilayer systems will be briefly discussed.

Automated summary

This study proposes a twisted bilayer structure composed of 2D systems and investigates its stable quadratic-band-touching points and exotic physics. The research reveals that exactly flat bands can emerge at specific magic angles with high Chern numbers. Moreover, the effect of Coulomb interactions is considered, and the ground state supports the quantum anomalous Hall effect.