Materials Science and Engineering Special Seminar

Abstract

The physical properties in magnetic-ordered materials were ultimately believed to rely on the symmetry theory of magnetic groups. Recently, it has come to light that a more comprehensive group, known as spin group, which combines separate spin and spatial operations, is necessary to fully characterize the geometry and underlying properties of magnetic-ordered materials such as altermagnets [1]. In this talk, we introduce the recent developments of spin group theory, including extensive enumeration of over 100000 spin space groups, identification of spin groups for collinear, coplanar, and noncoplanar configurations, and derivation of irreducible co-representations in momentum space leading to more energy degeneracies that are disallowed by magnetic groups [1,2,3]. We further show some theoretical and experimental results of spin group applications in understanding physical effects beyond the framework of magnetic groups. Examples include quadratic spin splitting effects in antiferromagnet MnTe2 [4], chiral Dirac fermions in antiferromagnet CoNb3S6 [5,6], and correlation enhanced spin-orbit coupling effect [7].

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

[2] Ren et al. arXiv:2307.10369 (2023).

[3] Chen et al. arXiv:2307.12366 (2023).

[4 Zhu et al. Nature in press (2024).

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

[6] Zhang et al. Chin. Phys. Lett. 40, 126101 (2023).

[7] Li et al. Nat. Commun. 13, 919 (2022).

Bio

Qihang Liu, Professor Qihang Liu is currently a tenured professor in Southern University of Science and Technology, Shenzhen, China. He obtained his bachelor and Ph.D. degree from School of Physics, Peking University. After graduation, he has served as a postdoctoral researcher at Northwestern University and as a research associate at the University of Colorado Boulder. Prof. Liu is engaged in computational condensed matter physics, with a recent focus on new theories and effects of symmetry in magnetic systems with spin-local moment-orbital coupling. He has authored more than 90 SCI papers with an H-index of 36. As an independent PI, he has published 7 PRLs, 4 PRXs, 3 Nat. Commun., etc, as corresponding authors. He has been consecutively selected as a top 2% global scientist by Stanford University from 2021 to 2023.