Emergence of Nontrivial Low‐Energy Dirac Fermions in Antiferromagnetic EuCd2As2

作者：Junzhang Ma, Han Wang, Simin Nie, Changjiang Yi, Yuanfeng Xu, Hang Li, Jasmin Jandke, Wulf Wulfhekel, Yaobo Huang, Damien J. West, Pierre Richard, Alla Chikina, Vladimir N. Strocov, Joël Mesot, Hongming Weng, Shengbai Zhang, Youguo Shi, Tian Qian, Ming Wen Shi, Hong Q. Ding · 发表于：Advanced Materials · 年份：2020 · DOI：10.1002/adma.201907565 · 被引用次数：93 · 研究领域：Topological Materials and Phenomena、Graphene research and applications、Advanced Condensed Matter Physics

Abstract Parity‐time symmetry plays an essential role for the formation of Dirac states in Dirac semimetals. So far, all of the experimentally identified topologically nontrivial Dirac semimetals (DSMs) possess both parity and time reversal symmetry. The realization of magnetic topological DSMs remains a major issue in topological material research. Here, combining angle‐resolved photoemission spectroscopy with density functional theory calculations, it is ascertained that band inversion induces a topologically nontrivial ground state in EuCd2As2. As a result, ideal magnetic Dirac fermions with simplest double cone structure near the Fermi level emerge in the antiferromagnetic (AFM) phase. The magnetic order breaks time reversal symmetry, but preserves inversion symmetry. The double degeneracy of the Dirac bands is protected by a combination of inversion, time‐reversal, and an additional translation operation. Moreover, the calculations show that a deviation of the magnetic moments from the c‐axis leads to the breaking of C3 rotation symmetry, and thus, a small bandgap opens at the Dirac point in the bulk. In this case, the system hosts a novel state containing three different types of topological insulator: axion insulator, AFM topological crystalline insulator (TCI), and higher order topological insulator. The results provide an enlarged platform for the quest of topological Dirac fermions in a magnetic system.