报告题目：Spin group symmetry in magnetic materials

报告人：刘奇航副教授  南方科技大学物理系

报告时间：2022 年 12月 28 日下午 15:00-16:00

报告地点：腾讯会议 414-459-875

报告摘要：Symmetry formulated by group theory plays an essential role with respect to the laws of nature, from fundamental particles to condensed matter systems. In this talk, we elucidate that the crystallographic symmetries 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 as spin group, is required. We then derive the classifications of spin “point groups” describing coplanar and collinear magnetic structures, and the irreducible co-representations of spin “space groups” illustrating more energy degeneracies that are disallowed by magnetic groups.

These results directly give rise to our further discovery of SOC-free topological phases. Here we give two examples. One is the new antiunitary symmetries that protect SOC-free Z2 topological phases with unprecedented surface-node structures. The other is a massless Dirac-like field yet linking two Weyl fields with the identical chirality. Such symmetry is hidden in certain solid-state spin-1/2 systems with negligible SOC. Therefore, the existence of the corresponding quasiparticle, dubbed as flavor Weyl fermion, cannot be explained by the conventional (magnetic) space group framework. For material realization, we show that the transition metal chalcogenide CoNb3S6 with experimentally confirmed collinear antiferromagnetic order is ideal for flavor Weyl semimetal under the approximation of vanishing SOC.

References

Liu et al. Phys. Rev. X 12, 021016 (2022)

Liu et al. The Innovation 3, 100343 (2022)

报告人简介：刘奇航，南方科技大学副教授，本科及博士均毕业于北京大学物理学院，曾任美国西北大学博士后、美国科罗拉多大学博尔德分校助理研究员；主要从事以密度泛函理论为主的凝聚态理论研究，研究兴趣包括对称性诱导的自旋轨道新效应，以及设计和筛选相关的新材料。近工作期间发表包括Nat. Phys.、Nat. Commun.、Phys. Rev. X、Phys, Rev. Lett.等多篇学术论文，引用超过5700次，H因子为30；2018年入选“国家特聘青年专家”；2020年国家重点研发计划-量子调控与量子信息重点专项（青年项目）负责人；2021-2022年入选斯坦福大学发布的全球前2%顶尖科学家榜单（World’s Top 2% Scientists）。

以上内容由大学时代综合整理自互联网，实际情况请以官方资料为准。