Realization of the Haldane Chern insulator in a moir\'e lattice

TL;DR

This paper reports the first experimental realization of a Haldane Chern insulator in a moiré bilayer system, demonstrating topological quantum states in solid-state materials through engineered lattice and magnetic field effects.

Contribution

It demonstrates the realization of a Haldane Chern insulator in a moiré lattice, bridging theoretical models and experimental solid-state topological physics.

Findings

Observation of a Chern number c=1 in MoTe2/WSe2 bilayers

Identification of a quantum spin Hall insulator with a tunable charge gap

Magneto-transport evidence supporting the topological phase transition

Abstract

The Chern insulator displays a quantized Hall effect without Landau levels. In a landmark paper in 1988, Haldane showed that a Chern insulator could be realized through complex next-nearest-neighbor hopping in a honeycomb lattice. Despite its profound impact on the field of topological physics and recent implementation in cold-atom experiments, the Haldane model has remained elusive in solid-state materials. Here, we report the experimental realization of a Haldane Chern insulator in AB-stacked MoTe2/WSe2 moir\'e bilayers, which form a honeycomb moir\'e lattice with two sublattices residing in different layers. We show that the moir\'e bilayer filled with two charge particles per unit cell is a quantum spin Hall (QSH) insulator with a tunable charge gap. Under a small out-of-plane magnetic field, it becomes a Chern insulator with Chern number c=1 from magneto-transport studies. The results are qualitatively captured by a generalized Kane-Mele tight-binding Hamiltonian. The Zeeman field splits the QSH insulator into two halves of opposite valley--one with a positive and the other a negative moir\'e band gap. Our study highlights the unique potential of semiconductor moir\'e materials in engineering topological lattice Hamiltonians.