学术活动
凝聚态
【凝聚态物理-北京大学论坛2023年第14期(总566期)】磁性材料中的自旋群对称性及应用
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主讲人: 刘奇航(南方科技大学)
地点: 物理大楼西楼202报告厅
时间: 2023年6月1日(星期四)15:00-16:30
主持 联系人: 李新征 xzli@pku.edu.cn
主讲人简介: 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(2003-2012),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;主要从事计算凝聚态物理研究,研究兴趣聚焦于量子材料中新奇的多自由度耦合现象,包括自旋-局域磁矩-轨道耦合作用下的对称性新理论和新效应,以及相关的新材料设计筛选。发表SCI论文80余篇,H指数34。2018年作为独立PI后发表通讯作者文章30余篇,包括11篇PRL/X、4篇Nat. Commun.、3篇Natl. Sci. Rev.等。2020年作为项目负责人获批国家重点研发计划“量子调控与量子信息”重点专项(青年项目),2022年获批深圳市杰青项目,2021与2022年连续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)。

  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 is an appropriate approximation, are considerably larger than the conventional magnetic groups [1]. 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 new symmetries directly give rise to further discoveries without any relativistic origins, including spin splitting, Z2 topological classification and new quasiparticles [1,2]. Using angle-resolved photoemission spectroscopy measurements and density functional theory calculations, we demonstrate the existence of such spin splitting effect in a noncoplanar antiferromagnet MnTe2 [3], and the spectral evidence of chiral Dirac fermions in a collinear antiferromagnet CoNb3S6 [4].

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

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

[3] Zhu et al. arXiv:2303.04549

[4] Zhang et al. arXiv:2301.12201