Valley-Polarized Quantum Anomalous Hall State in Moir\'e MoTe$_2$/WSe$_2$ Heterobilayers

TL;DR

This paper explains how lattice relaxation in moiré MoTe2/WSe2 heterobilayers induces pseudo-magnetic fields, leading to topologically nontrivial quantum valley Hall and quantum anomalous Hall states consistent with recent experiments.

Contribution

It proposes a mechanism involving pseudo-magnetic fields from lattice relaxation to explain the emergence of topological states in heterobilayer TMDs, a phenomenon previously thought to be trivial.

Findings

Pseudo-magnetic fields induce moiré bands with finite Chern numbers.

Full-filling ν=2 results in a quantum valley Hall insulator.

Half-filling ν=1 leads to a valley-polarized quantum anomalous Hall state.

Abstract

Moir\'e heterobilayer transition metal dichalcogenides (TMDs) emerge as an ideal system for simulating the single-band Hubbard model and interesting correlated phases have been observed in these systems. Nevertheless, the moir\'e bands in heterobilayer TMDs were believed to be topologically trivial. Recently, it was reported that both a quantum valley Hall insulating state at filling $\nu=2$ (two holes per moir\'e unit cell) and a valley-polarized quantum anomalous Hall state at filling $\nu=1$ were observed in AB stacked moir\'e MoTe$_2$/WSe$_2$ heterobilayers. However, how the topologically nontrivial states emerge is not known. In this work, we propose that the pseudo-magnetic fields induced by lattice relaxation in moir\'e MoTe$_2$/WSe$_2$ heterobilayers could naturally give rise to moir\'e bands with finite Chern numbers. We show that a time-reversal invariant quantum valley Hall insulator is formed at full-filing $\nu=2$, when two moir\'e bands with opposite Chern numbers are filled. At half-filling $\nu=1$, Coulomb interaction lifts the valley degeneracy and results in a valley-polarized quantum anomalous Hall state, as observed in the experiment. Our theory identifies a new way to achieve topologically non-trivial states in heterobilayer TMD materials.