Quantum anomalous Hall effect from intertwined moir\'e bands

TL;DR

This paper reports the observation of a quantum anomalous Hall effect in AB-stacked MoTe2/WSe2 moiré heterobilayers, demonstrating electric-field control of band topology and a correlation-driven topological phase transition without bulk gap closure.

Contribution

It introduces the first observation of a QAH effect in moiré heterobilayers with electric-field tunable topology and correlation effects, revealing a novel topological phase transition.

Findings

Quantized Hall resistance at zero magnetic field.

Electric-field-induced topological phase transition.

Transition from Mott insulator to QAH insulator without gap closure.

Abstract

Electron correlation and topology are two central threads of modern condensed matter physics. Semiconductor moir\'e materials provide a highly tunable platform for studies of electron correlation. Correlation-driven phenomena, including the Mott insulator, generalized Wigner crystals, stripe phases and continuous Mott transition, have been demonstrated. However, nontrivial band topology has remained elusive. Here we report the observation of a quantum anomalous Hall (QAH) effect in AB-stacked MoTe2/WSe2 moir\'e heterobilayers. Unlike in the AA-stacked structures, an out-of-plane electric field controls not only the bandwidth but also the band topology by intertwining moir\'e bands centered at different high-symmetry stacking sites. At half band filling, corresponding to one particle per moir\'e unit cell, we observe quantized Hall resistance, h/e2 (with h and e denoting the Planck's constant and electron charge, respectively), and vanishing longitudinal resistance at zero magnetic field. The electric-field-induced topological phase transition from a Mott insulator to a QAH insulator precedes an insulator-to-metal transition; contrary to most known topological phase transitions, it is not accompanied by a bulk charge gap closure. Our study paves the path for discovery of a wealth of emergent phenomena arising from the combined influence of strong correlation and topology in semiconductor moir\'e materials.