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

Abstract

We propose an alternative mechanism for the quantum anomalous Hall (QAH) effect in the $AB$ stacked $\mathrm{Mo}{\mathrm{Te}}_{2}/\mathrm{W}{\mathrm{Se}}_{2}$ 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 moir\'e lattices of the two layers are shifted to form a honeycomb lattice. Initially, the system is in a layer-polarized Mott insulator at ${\ensuremath{\nu}}_{T}=1$. 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 $p\ifmmode\pm\else\textpm\fi{}ip$ exciton condensation in a certain parameter regime, which leads to a Chern insulator with Chern number $\text{C}=\ifmmode\pm\else\textpm\fi{}1$. 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.