报告题目：Ultrafast dynamics of low-energy collective excitations in a 2D antiferromagnet MnBi2Te4

报告时间：12月5日 周二 中午12:00

报告地点：唐仲英楼B501

报告摘要：The atomically thin MnBi2Te4 crystal is a novel magnetic topological insulator, exhibiting exotic quantum physics. In this work, using time-resolved optical techniques, we report a systematic investigation of coherent interlayer phonons, ultrafast (de)magnetization and coherent magnon dynamics in few-layer MnBi2Te4 as a function of layer number, temperature and applied magnetic field. Pronounced coherent phonon oscillations from the interlayer breathing mode are directly observed in the time domain and further confirmed by ultralow-frequency Raman spectroscopy measurements. Below the Neel temperature, we observe laser-induced (de)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. Surprisingly, the magnetic state dependence and magnons are observed not only in time-resolved Kerr rotation and but also in time-resolved reflectivity measurements, indicating a strong correlation between the magnetic state and the electronic structure. These measurements present the first comprehensive overview of ultrafast interlayer phonon and spin dynamics in this novel 2D antiferromagnet, paving 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.

[1] Bartram et al., npj Quantum Materials 7, 84 (2022).

[2] Bartram et al., Science Bulletin (2023)

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. 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.