Li Yang, Li Jiaheng, Li Yang, Ye Meng, Zheng Fawei, Zhang Zetao, Fu Jingheng, Duan Wenhui, Xu Yong
State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.
Frontier Science Center for Quantum Information, Beijing 100084, China.
Phys Rev Lett. 2020 Aug 21;125(8):086401. doi: 10.1103/PhysRevLett.125.086401.
Quantum anomalous Hall (QAH) insulator is the key material to study emergent topological quantum effects, but its ultralow working temperature limits experiments. Here, by first-principles calculations, we find a family of stable two-dimensional (2D) structures generated by lithium decoration of layered iron-based superconductor materials Fe X(X=S,Se,Te), and predict room-temperature ferromagnetic semiconductors together with large-gap high-Chern-number QAH insulators in the 2D materials. The extremely robust ferromagnetic order is induced by the electron injection from Li to Fe and stabilized by strong ferromagnetic kinetic exchange in the 2D Fe layer. While in the absence of spin-orbit coupling (SOC), the ferromagnetism polarizes the system into a half Dirac semimetal state protected by mirror symmetry, the SOC effect results in a spontaneous breaking of mirror symmetry and introduces a Dirac mass term, which creates QAH states with sizable gaps (several tens of meV) and multiple chiral edge modes. We also find a 3D QAH insulator phase featured by a macroscopic number of chiral conduction channels in bulk LiOH-LiFe X. The findings open new opportunities to realize novel QAH physics and applications at high temperatures.
量子反常霍尔（QAH）绝缘体是研究新兴拓扑量子效应的关键材料，但其超低的工作温度限制了实验。在此，通过第一性原理计算，我们发现了一族由层状铁基超导材料Fe X（X = S、Se、Te）的锂修饰产生的稳定二维（2D）结构，并预测了这些二维材料中的室温铁磁半导体以及大带隙高陈数QAH绝缘体。极其稳健的铁磁序由从Li到Fe的电子注入诱导，并通过二维Fe层中的强铁磁动力学交换得以稳定。在没有自旋轨道耦合（SOC）的情况下，铁磁性将系统极化到由镜面对称性保护的半狄拉克半金属态，而SOC效应导致镜面对称性的自发破缺并引入狄拉克质量项，从而产生具有可观带隙（几十毫电子伏）和多个手性边缘模式的QAH态。我们还发现了一种三维QAH绝缘体相，其特征是在块状LiOH-LiFe X中有大量的手性传导通道。这些发现为在高温下实现新型QAH物理和应用开辟了新机会。
