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

Abstract

Studies of twisted moiré 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 moiré 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 2e^{2}/hc at certain filling. Furthermore, the possible physical realization of such twisted bilayer systems will be briefly discussed.