Commensurate and Incommensurate Chern Insulators in Magic-angle Bilayer Graphene

作     者：Zhang, Zaizhe Yang, Jingxin Xie, Bo Feng, Zuo Zhang, Shu Watanabe, Kenji Taniguchi, Takashi Yang, Xiaoxia Dai, Qing Liu, Tao Liu, Donghua Liu, Kaihui Song, Zhida Liu, Jianpeng Lu, Xiaobo 

作者机构：International Center for Quantum Materials School of Physics Peking University Beijing100871 China National Engineering Research Center of Electromagnetic Radiation Control Materials University of Electronic Science and Technology of China Chengdu611731 China School of Physical Science and Technology ShanghaiTech University Shanghai201210 China State Key Laboratory for Mesoscopic Physics Frontiers Science Centre for Nano-optoelectronics School of Physics Peking University Beijing100871 China CAS Key Laboratory of Nanophotonic Materials and Devices CAS Key Laboratory of Standardization and Measurement for Nanotechnology CAS Center for Excellence in Nanoscience National Center for Nanoscience and Technology Beijing100871 China Research Center for Electronic and Optical Materials National Institute of Material Sciences 1-1 Namiki Tsukuba305-0044 Japan Research Center for Materials Nanoarchitectonics National Institute of Material Sciences 1-1 Namiki Tsukuba305-0044 Japan School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai200240 China School of Materials and Energy University of Electronic Science and Technology of China Chengdu611731 China Collaborative Innovation Center of Quantum Matter Beijing100871 China Hefei National Laboratory Hefei230088 China 

出 版 物：《arXiv》 (arXiv)

年 卷 期：2024年

核心收录：

主　　题：Degrees of freedom (mechanics) 

摘      要：The interplay between strong electron-electron interaction and symmetry breaking can have profound influence on the topological properties of materials1–4. In magic angle twisted bilayer graphene (MATBG), the flat band with a single SU(4) flavor associated with the spin and valley degrees of freedom gains non-zero Chern number when C2z symmetry or C2zT symmetry is broken. Electron-electron interaction can further lift the SU(4) degeneracy, leading to the Chern insulator states5–14. Here we report a complete sequence of zero-field Chern insulators at all odd integer fillings (ν = ±1, ±3) with different chirality (C = 1 or -1) in hBN aligned MATBG which structurally breaks C2z symmetry. The Chern states at hole fillings (v = -1, -3), which are firstly observed in this work, host an opposite chirality compared with the electron filling scenario. By slightly doping the v = ±3 states, we have observed new correlated insulating states at incommensurate moiré fillings which is highly suggested to be intrinsic Wigner crystals according to our theoretical calculations. Remarkably, we have observed prominent Streda-formula violation around v = -3 state. By doping the Chern gap at v = -3 with notable number of electrons at finite magnetic field, the Hall resistance Ryx robustly quantizes to ~ h/e2 whereas longitudinal resistance Rxx vanishes, indicating that the chemical potential is pinned within a Chern gap, forming an incommensurate Chern insulator. By providing the first experimental observation of zero-field Chern insulators in the flat valence band, our work fills up the overall topological framework of MATBG with broken C2z symmetry. Our findings also demonstrate that doped topological flat band is an ideal platform to investigate exotic incommensurate correlated topological states. © 2024, CC BY-NC-SA.