反铁磁半金属 EuCd2Pn2（Pn = As,Sb）中磁交换诱导的外尔态

由于丰富的拓扑量子效应及巨大的潜在应用价值，拓扑材料逐渐成为凝聚态物理前沿的研究材料体系。其中，作为与石墨烯具有相似电子结构的材料，三维拓扑半金属吸引了越来越多的研究兴趣。目前已知的拓扑半金属大多为非磁性的，而磁性拓扑半金属数量有限，与非磁性拓扑半金属相比较，研究开展的还比较少。磁性与拓扑之间的相互作用能够导致非常规的物理性质，如反常霍尔效应甚至量子反常霍尔效应等。此外，在一些具有特殊磁结构的拓扑半金属中，施加外磁场能够调制其自旋结构，从而影响其拓扑能带结构。在该综述中，笔者将详细介绍利用外磁场在 EuCd2Pn2 (Pn = As, Sb) 反铁磁半金属材料中通过调制自旋结构从而改变晶体结构对称性来诱导拓扑相变。此外，笔者也将简单介绍包括 GdPtBi 和 MnBi2Te4 在内的几个相关材料。该综述中讨论的外磁场调控的磁交换诱导的拓扑相变不仅有望应用于拓扑器件，也有助于为理解磁性与拓扑态之间的紧密关联提供新的线索，对于设计新的磁性拓扑材料有启发意义。综述最后，笔者对发展磁性拓扑半金属做了一些简单展望。

Magnetic exchange induced Weyl states in the antiferromagnetic semimetals EuCd2Pn2 (Pn = As,Sb)

Three-dimensional (3D) topological semimetals (TSMs) have arrested special attentions as 3D analogues to graphene. The TSMs, for example, the Dirac and Weyl semimetals, show an array of intriguing physical properties arising from the electronic band structure topology, which have therefore been under immense investigations. Most of the known TSMs are nonmagnetic, whereas the magnetic TSMs are very few and remain less investigated. The interplay between magnetism and nontrivial topological states can result in exceptional physical properties, such as anomalous or even quantum anomalous Hall effect. In some TSMs with peculiar magnetic structures, the magnetic exchange could be tuned by application of an external magnetic field, which consequently can affect the topological properties. We review herein the family of antiferromagnetic semimetals EuCd2Pn2 (Pn = As, Sb) which exhibit topological phase transitions induced by an external magnetic field through tuning the spin structures and hence the structure symmetries that are protecting the topological states. Besides, we will also briefly review several other related materials including the GdPtBi and MnBi2Te4. The herein discussed magnetism induced topological phase transition provides potential use in novel topological devices since the topological states could be conveniently controlled by external magnetic field. Furthermore, it also contributes important clues toward understanding the intimate relation between magnetism and topological states, which are instructive for designing new magnetic topological phases. At the end of this review, we also give a short perspective for the development of the magnetic TSMs.