清华大学
报告人简介
Prof. Luyi Yang received her B.S. in physics and mathematics from Tsinghua University (2007). She earned her Ph.D. in physics from the University of California at Berkeley (2013). Then she worked as a Los Alamos Director’s Postdoctoral Fellow at the National High Magnetic Field Laboratory at Los Alamos. She became an Assistant Professor at the University of Toronto in 2016. She joined the Department of Physics, Tsinghua University as an Associate Professor in September 2019. She was awarded Canada Research Chair, CIFAR Global Scholar and Young Thousand Talents. Her research interests focus on the development of novel optical spectroscopies and their application to problems at the forefront of condensed matter and materials physics.
报告摘要
Magnetic topological materials not only exhibit novel exotic quantum phenomena like the quantum anomalous Hall effect but also hold promise for various applications, including information storage and dissipationless transport. In this talk, I will discuss our recent ultrafast studies of spin dynamics in two types of magnetic topological materials using time-resolved optical techniques.
In the first part, we report a systematic investigation of ultrafast magnetization and coherent magnon dynamics in few-layer MnBi2Te4, a novel magnetic topological insulator, as a function of layer number, temperature and applied magnetic field. Below the Neel temperature, we observe laser-induced magnetization processes that can be used to accurately track the distinct magnetic states in different magnetic field regimes, including showing clear odd-even layer number effects. In addition, strongly field-dependent antiferromagnetic magnon modes with tens of gigahertz frequencies are optically generated and directly observed in the time domain. These measurements pave the way for potential applications in 2D antiferromagnetic spintronics and magnonics as well as further studies of ultrafast control of both magnetization and topological quantum states.
In the second part, we study coherent magnon dynamics in topological kagome ferromagnet Co3Sn2S2. To our surprise, we directly observed two magnon modes in the terahertz range in the time domain for the first time. This marks the highest magnon resonance frequencies ever reported in ferromagnets. Supported by a microscopic model, we propose that these dual modes emerge from the low-energy collective excitations of coupled spin and orbital magnetic moments in the presence of ferromagnetic long-ranger order on the kagome lattice. Therefore, our work uncovers a novel type of magnons due to orbital magnetic moments and lays the foundation for the development of terahertz spintronic devices using topological kagome ferromagnets.
[1] Bartram et al., Science Bulletin 68, 2734-2742 (2023)
[2] Che et al., in preparation (2024)
报告地点：中国科学院物理研究所M253会议室
邀请人：孟 胜 研究员
联系人：万 源 研究员
汪非凡 副研究员
田春璐 cltian@iphy.ac.cn
主办方：中国科学院物理研究所、松山湖材料实验室