School of Applied and Engineering Physics and Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA.
Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China.
Nature. 2021 Dec;600(7890):641-646. doi: 10.1038/s41586-021-04171-1. Epub 2021 Dec 22.
Electron correlation and topology are two central threads of modern condensed matter physics. Semiconductor moiré materials provide a highly tuneable 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, non-trivial band topology has remained unclear. Here we report the observation of a quantum anomalous Hall effect in AB-stacked MoTe /WSe moiré heterobilayers. Unlike in the AA-stacked heterobilayers, an out-of-plane electric field not only controls the bandwidth but also the band topology by intertwining moiré bands centred at different layers. At half band filling, corresponding to one particle per moiré unit cell, we observe quantized Hall resistance, h/e (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 quantum anomalous Hall 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 way for discovery of emergent phenomena arising from the combined influence of strong correlation and topology in semiconductor moiré materials.
电子关联和拓扑是现代凝聚态物理的两个核心主线。半导体莫尔材料为研究电子关联提供了一个高度可调谐的平台。已经证明了关联驱动的现象，包括莫特绝缘体、广义维格纳晶体、条纹相和连续莫特转变。然而，非平凡的能带拓扑结构仍然不清楚。在这里，我们报告了在 AB 堆叠的 MoTe/WSe 莫尔异质双层中观察到量子反常霍尔效应。与 AA 堆叠的异质双层不同，外电场不仅通过缠绕位于不同层的莫尔能带来控制带宽，还控制能带拓扑。在半带填充时，对应于每个莫尔单元的一个粒子，我们观察到量子化的霍尔电阻 h/e（其中 h 和 e 分别表示普朗克常数和电子电荷），并且在零磁场下纵向电阻消失。从莫特绝缘体到量子反常霍尔绝缘体的电场诱导拓扑相变先于绝缘-金属相变。与大多数已知的拓扑相变不同，它不是伴随着体电荷带隙闭合。我们的研究为在半导体莫尔材料中发现由强关联和拓扑共同作用产生的新兴现象铺平了道路。
