近日，美国华盛顿大学Xiaodong Xu团队研究了分数Chern绝缘体中较高平带的铁磁性和拓扑结构。这一研究成果于2025年3月20日发表在《自然—物理学》杂志上。
最近对莫尔分数Chern绝缘体中分数量子反常霍尔效应的观察为研究零磁场任意子提供了机会。可能实现非阿贝尔任意子的一种方法是设计更高的平坦Chern带，模仿更高的朗道能级。课题组研究了扭曲MoTe2双层中第二莫尔微带的相互作用、拓扑结构和铁磁性。在第二个小带的半填充时，他们观察到自发铁磁性和初始的Chern绝缘体状态。
顶部两个莫尔平带的Chern数在3.1°以上的扭曲角上表现出相反的符号，但在2.6°附近具有相同的符号，这与理论预测一致。在2.6°器件中，由于相反谷之间的能带交叉，增加磁场会引起拓扑相变，从而导致Chern数为C = −2的紧急状态. 此外，第二谷极化带半填充时的绝缘状态表明，电荷有序态优于分数Chern绝缘体态。这些发现为理解更高的平坦Chern带奠定了基础，这对发现非阿贝尔分数Chern绝缘体至关重要。
附：英文原文
Title: Ferromagnetism and topology of the higher flat band in a fractional Chern insulator
Author: Park, Heonjoon, Cai, Jiaqi, Anderson, Eric, Zhang, Xiao-Wei, Liu, Xiaoyu, Holtzmann, William, Li, Weijie, Wang, Chong, Hu, Chaowei, Zhao, Yuzhou, Taniguchi, Takashi, Watanabe, Kenji, Yang, Jihui, Cobden, David, Chu, Jiun-haw, Regnault, Nicolas, Bernevig, B. Andrei, Fu, Liang, Cao, Ting, Xiao, Di, Xu, Xiaodong
Issue&Volume: 2025-03-20
Abstract: The recent observation of the fractional quantum anomalous Hall effect in moiré fractional Chern insulators provides an opportunity to investigate zero magnetic field anyons. One approach for potentially realizing non-abelian anyons is to engineer higher flat Chern bands that mimic higher Landau levels. We investigate the interaction, topology and ferromagnetism of the second moiré miniband in twisted MoTe2 bilayers. At half-filling of the second miniband, we observed spontaneous ferromagnetism and an incipient Chern insulator state. The Chern numbers of the top two moiré flat bands exhibited opposite signs for twist angles above 3.1° but had the same sign near 2.6°, consistent with theoretical predictions. In the 2.6° device, increasing the magnetic field induced a topological phase transition due to band-crossing between opposite valleys, resulting in an emergent state with Chern number C=2. Additionally, an insulating state at half-filling of the second valley-polarized band indicates that a charge-ordered state is favoured over the fractional Chern insulator state. These findings lay a foundation for understanding the higher flat Chern bands, which are crucial for the discovery of non-abelian fractional Chern insulators.
DOI: 10.1038/s41567-025-02804-0
Source: https://www.nature.com/articles/s41567-025-02804-0