| Time：1150603 (Wed.) 14:20~16:20 Speaker：Prof.郭光宇(GUO, Guang-Yu) 國立臺灣大學物理學系/Department of Physics, National Taiwan University Title：Chirality-induced Phenomena in Quantum Materials Abstract： Chirality (handedness) refers to the asymmetry characterized by non-superimposable mirror images of an object. In chiral crystals, there is no mirror symmetry (M) nor spatial inversion symmetry (P). The broken P-symmetry enables chiral crystals to exhibit the even-order nonlinear responses to the electromagnetic fields, e.g., nonlinear Hall effect (NLHE), second harmonic generation (SHG) and photogalvanic effect (PGE). In addition, chirality enables chiral crystal to exhibit novel properties, e.g., optical activity (natural circular dichroism) and quantized circular PGE (CPGE). Spin chirality in noncollinear magnetic structures can cause unexpected phenomena in solids by either generating Berry curvature in momentum and real spaces or breaking Kramer spin degeneracy in the electronic band structure. In this talk, I will present (1) spin-chirality induced quantum topological Hall effect [1] and topological magneto-optical Kerr and Faraday rotations [2] in noncoplanar antiferromagnets, (2) crystal chirality-induced magneto-optical effects in collinear antiferromagnets (altermagnets) [3], and magnetic moments of chiral phonons in chiral crystals [4], as revealed by our first-principles quantum mechanical calculations. The speaker thanks many collaborators, especially Jian Zhou, Qi-Feng Liang, Wanxiang Feng, Yugui Yao, and P. V. Sreenivasa. [1] J. Zhou, Q.-F. Liang, H. Weng, Y. B. Chen, S.-H. Yao, Y.-F. Chen, J. Dong and G.-Y. Guo, Predicted quantum topological Hall effect and noncoplanar antiferromagnetism in K1/2RhO2, Phys. Rev. Lett. 116, 256601 (2016). [2] W. Feng, J.-P. Hanke, X. Zhou, G.-Y. Guo, S. Blügel, Y. Mokrousov and Y. Yao, Topological magneto-optical effects and their quantization in noncoplanar antiferromagnets, Nature Commun. 11, 118 (2020). [3] X. Zhou, W. Feng, X. Yang, G.-Y. Guo and Y. Yao, Crystal chirality magneto-optical effects in collinear antiferromagnets, Phys. Rev. B 104, 024401 (2021). [4] P. V. Sreenivasa Reddy and G.-Y. Guo, Coexistent topological and chiral phonons in chiral RhGe: An ab initio study, arXiv: 2410.16000 (2024) Brief Bio： Guang-Yu Guo is currently an NTU Chair Professor of National Taiwan University (NTU) ( https://webpageprodvm.ntu.edu.tw/enphysics/gyguo.htm? ). He received his PhD from Cambridge University, UK in 1987. He joined the NTU Physics Faculty in 1998 after working in Daresbury Laboratory, UK for 11 years as a postdoc, higher and senior staff scientist. He also worked in National Chengchi University as a Chair Professor and the founding director of the Graduate Institute of Applied Physics during 2009-2013. He has been vigorously conducting research in condensed matter and materials physics in the past 40 years, publishing over 320 journal papers with 18,000+ citations and h-index of 68 (google scholar: https://scholar.google.com/citations?user=XyumTigAAAAJ&hl=zh-TW ). He has won several academic awards and honors including the National Science Council Outstanding Research Awards (1998, 2004, 2009) as well as the Ministry of Education (MOE) 57th Academic Award (2013). He held the MOE 19th (2016-2019) and 27th (2024-2027) National Chair Professorship. He is an elected Fellow of the TPS (2005), APS (USA) (2005) and Institute of Physics (UK) (2013). Place：S101, Gongguan Campus, NTNU |
