Excitonic Chern insulator and kinetic ferromagnetism in MoTe$_2$/WSe$_2$ moiré bilayer

Abstract: We propose a new mechanism for quantum anomalous Hall (QAH) effect in the AB stacked MoTe$_2$/WSe$_2$ system. Based on the observation that the inter-layer tunneling is suppressed in the AB stacking, we consider a model with two layers coupled through the Coulomb interaction. The moir\'e lattices of the two layers are shifted to form a honeycomb lattice together. Initially, the system is in a layer-polarized Mott insulator at $\nu_T=1$. But with a displacement field, an equal number of holes and electrons are doped into the two layers respectively and they form inter-layer exciton condensation. Through mean field theory, we find p$\pm$ip exciton condensation in a certain parameter regime, which leads to a Chern insulator with Chern number $C=\pm 1$. The valleys are polarized due to the kinetic energy instead of interaction. But the polarization in the two layers can be either the same or opposite depending on small perturbations away from a symmetric point. As a result, both valley polarized and inter-valley coherent (IVC) Chern insulator phases are possible. The latter has the same spin $S_z$ in the two layers.