Cascade of zero-field Chern insulators in magic-angle bilayer graphene

作者：Zaizhe Zhang, Jingxin Yang, Bo Xie, Feng Zuo, Shu Zhang, Kenji Watanabe, Takashi Taniguchi, Xiaoxia Yang, Qing Dai, Donghua Liu, Kaihui Liu, Zhida Song, Tao Liu, Jianpeng Liu, Xiaobo Lu · 发表于：National Science Review · 年份：2025 · DOI：10.1093/nsr/nwaf265 · 被引用次数：5 · 研究领域：Graphene research and applications、Crystallography and Radiation Phenomena、Topological Materials and Phenomena

ABSTRACT The interplay between strong electron-electron interactions and symmetry breaking can have a profound influence on the topological properties of materials. 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 a non-zero Chern number when C2z symmetry or C2zT symmetry is broken. Electron-electron interactions can further lift the SU(4) degeneracy, leading to Chern insulator states. Here, we report a complete sequence of zero-field Chern insulators at all odd-integer fillings (ν = ±1, ±3) with different chiralities (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. Furthermore, at the valence band filling ν = −7/2, the zero-field symmetry broken Chern insulator with C = −1 can be observed. Remarkably, a prominent Streda-formula violation around the v = −3 state has been observed. By doping the Chern gap at v = −3 with a notable number of electrons at finite magnetic field, the Hall resistance Ryx robustly quantizes to ∼h/e2, whereas the longitudinal resistance Rxx vanishes, indicating that the chemical potential is pinned within a Chern gap, forming the magnetic field stabilized incommensurate Chern insulator states. By providing the first experimental observation of zero-field Chern insulat...