近日，英属哥伦比亚大学的Joshua Folk及其研究小组与美国华盛顿大学的Matthew Yankowitz等人合作并取得一项新进展。经过不懈努力，他们发现扭曲石墨烯中莫尔驱动的拓扑电子晶体。相关研究成果已于2025年1月22日在国际权威学术期刊《自然》上发表。

该研究团队在扭曲的双层-三层石墨烯中观察到广义反常霍尔晶体的特征，其形成由莫尔势驱动。该晶体在每四个莫尔晶胞填充一个电子（ν=1/4）时形成，并使晶胞面积扩大为原来的四倍，同时伴随着整数量子反常霍尔效应的出现。该状态的陈数具有异常的可调性，并且可以通过电场和磁场在+1和-1之间可逆切换。在适中的磁场下，还出现了源自ν=1/3、1/2、2/3和3/2的其他几种拓扑电子晶体。相互作用修饰后的能带的量子几何形状可能与原始母带大不相同，这为未来发现关联驱动的拓扑现象提供了可能。

据悉，在稀薄的二维电子气中，库仑相互作用可以促使维格纳晶体的形成。尽管维格纳晶体在拓扑上是平凡的，但据预测，部分填充能带中的电子可以自发地打破连续的平移对称性和时间反演对称性，从而形成一种称为反常霍尔晶体的拓扑电子晶体。

附：英文原文

Title: Moiré-driven topological electronic crystals in twisted graphene

Author: Su, Ruiheng, Waters, Dacen, Zhou, Boran, Watanabe, Kenji, Taniguchi, Takashi, Zhang, Ya-Hui, Yankowitz, Matthew, Folk, Joshua

Issue&Volume: 2025-01-22

Abstract: In a dilute two-dimensional electron gas, Coulomb interactions can stabilize the formation of a Wigner crystal. Although Wigner crystals are topologically trivial, it has been predicted that electrons in a partially filled band can break continuous translational symmetry and time-reversal symmetry spontaneously, resulting in a type of topological electron crystal known as an anomalous Hall crystal. Here we report signatures of a generalized version of the anomalous Hall crystal in twisted bilayer–trilayer graphene, whose formation is driven by the moiré potential. The crystal forms at a band filling of one electron per four moiré unit cells (ν=1/4) and quadruples the unit-cell area, coinciding with an integer quantum anomalous Hall effect. The Chern number of the state is exceptionally tunable, and it can be switched reversibly between +1 and 1 by electric and magnetic fields. Several other topological electronic crystals arise in a modest magnetic field, originating from ν=1/3, 1/2, 2/3 and 3/2. The quantum geometry of the interaction-modified bands is likely to be very different from that of the original parent band, which enables possible future discoveries of correlation-driven topological phenomena.

DOI: 10.1038/s41586-024-08239-6

Source: https://www.nature.com/articles/s41586-024-08239-6