Excitonic Chern insulator and kinetic ferromagnetism in a MoTe2/WSe2 moire bilayer

We propose an alternative mechanism for the quantum anomalous Hall (QAH) effect in the AB stacked MoTe2/WSe2 system. Based on the observation that interlayer tunneling is suppressed in AB stacking, we consider a model with two layers coupled through the Coulomb interaction. The moire lattices of the two layers are shifted to form a honeycomb lattice. 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, forming interlayer exciton condensation. Through mean field theory, we find p +/- ip exciton condensation in a certain parameter regime, which leads to a Chern insulator with Chern number C = +/- 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. In particular, an intervalley-coherent (IVC) Chern insulator phase is possible, in agreement with the recent magnetic circular dichroism (MCD) measurement. Our work opens another direction in the search for a topologically nontrivial excitonic insulator with high angular momentum exciton pairing symmetry.