Valley-Polarized Quantum Anomalous Hall State in Moiré MoTe2/WSe2 Heterobilayers

Abstract

Moiré 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 moiré bands in heterobilayer TMDs were believed to be topologically trivial. Recently, it was reported that both a quantum valley Hall insulating state at filling ν ¼ 2 (two holes per moiré unit cell) and a valley-polarized quantum anomalous Hall state at filling ν ¼ 1 were observed in AB stacked moiré MoTe 2 =WSe 2 heterobilayers. However, how the topologically nontrivial states emerge is not known. In this Letter, we propose that the pseudomagnetic fields induced by lattice relaxation in moiré MoTe 2 =WSe 2 heterobilayers could naturally give rise to moiré bands with finite Chern numbers. We show that a timereversal invariant quantum valley Hall insulator is formed at full filling ν ¼ 2, when two moiré bands with opposite Chern numbers are filled. At half filling ν ¼ 1, the 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 nontrivial states in heterobilayer TMD materials.

Intrinsic spin Hall torque in a moire Chern magnet

“…1b). This is consistent with previous results on AB-stacked MoTe 2 /WSe 2 bilayers [3], where a magnetic Chern insulator arises due to the interplay of strong Coulomb repulsion and underlying Berry curvature of the moiré subbands [19][20][21][22][23].…”

Colloquium: Quantum anomalous Hall effect

“…For this reason, single-particle hybridization between layers is expected to be weak, making it less obvious how valley projected Chern bands could develop. Devakul and Fu, 2021, Xie et al, 2022, and Pan et al, 2021 have separately provided plausible scenarios for how Chern bands can emerge that rely on specific details of the bilayer moiré band electronic structure. The general lesson might be that topologically non-trivial bands are even more common in moiré materials than in atomic-scale crystals in which bands have a strong tendency to organize according to the atomic shells of constituent atoms.…”

Chiral Kondo lattice in doped MoTe 2 /WSe 2 bilayers

“…Here, we focus on the AB-stacked MoTe 2 /WSe 2 bilayer heterostructure of recent experimental (1) and theoretical (13)(14)(15)(16)(17)(18) interest and show that it realizes a chiral Kondo lattice. In this system, the lattice mismatch between the two materials leads to a hexagonal moiré lattice with a moiré lattice constant of a M ∼ 5 nm.…”

“…The first carriers added to the system go into the MoTe 2 layer, forming a correlated metal, which at n = 1 becomes a triangularlattice Mott insulator with 120 ∘ antiferromagnetic (AFM) order. At carrier concentration n = 1, decreasing Δ is predicted (14)(15)(16)(17)(18)27) and observed (1,2) to cause a transition to a quantum anomalous Hall (QAH) state, followed by a transition to a conventional metallic state. At Δ > 0, carriers in excess of the Mott concentration at half-filling (n = 1 per moiré unit cell) go into the WSe 2 band (if, as we assume, U > Δ) and are coupled to the spins of the Mott insulator via an exchange coupling J K ≏ t 2 h =Δ derived perturbatively from the interlayer hybridization t h so that the MoTe 2 /WSe 2 system can be described by an effective Kondo lattice model on the moiré scale whose study is the central topic of this paper.…”