Spin-Group Symmetry in Magnetic Materials with Negligible Spin-Orbit Coupling
Spin-Group Symmetry in Magnetic Materials with Negligible Spin-Orbit Coupling
复制标题
自旋轨道耦合可忽略不计的磁性材料中的自旋群对称性
DOI：
10.1103/physrevx.12.021016
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发表时间：
2022-04-21
影响因子：
12.5
通讯作者：
Liu, Qihang
中科院分区：
文献类型：
--
作者：
Liu, Pengfei;Li, Jiayu;Liu, Qihang
从基本粒子到凝聚态系统，群论所阐述的对称性在自然定律中扮演着重要的角色。在这里，通过结合对称性分析和模型计算，我们阐明了大量的轻元素磁性材料的晶体学对称群，其中忽略相对论自旋轨道耦合（SOC）是一个适当的近似，是相当大的比传统的磁组。因此，需要一个涉及部分解耦自旋和空间旋转的对称性描述，称为自旋群。我们推导出描述共面和共线磁结构的自旋点群的分类，以及自旋空间群的不可约共表示，说明了磁群不允许的更多能量简并。自旋群的一个结果是新的反幺正对称性，它以前所未有的表面节点结构保护了无SOC的Z（2）拓扑相。我们的工作不仅揭示了具有弱SOC的物质的物理实在性，而且为用统一群论理解所有具有和不具有SOC的固体提供了启示。
Symmetry formulated by group theory plays an essential role with respect to the laws of nature, from fundamental particles to condensed-matter systems. Here, by combining symmetry analysis and model calculations, we elucidate that the crystallographic symmetry groups of a vast number of magnetic materials with light elements, in which the neglect of relativistic spin-orbit coupling (SOC) is an appropriate approximation, are considerably larger than the conventional magnetic groups. Thus, a symmetry description that involves partially decoupled spin and spatial rotations, dubbed spin group, is required. We derive the classifications of spin point groups describing coplanar and collinear magnetic structures, and the irreducible corepresentations of spin space groups illustrating more energy degeneracies that are disallowed by magnetic groups. One consequence of the spin group is the new antiunitary symmetries that protect SOC-free Z(2) topological phases with unprecedented surface-node structures. Our work not only manifests the physical reality of materials with weak SOC, but also sheds light on the understanding of all solids with and without SOC by a unified group theory.