报告人：Prof. Junwei Liu（The Hong Kong University of Science and Technology）

时 间：2023年9月19日（星期二）下午14：00-15：30

地 点：良乡校区 物理实验中心229会议室

摘要：

In this talk, I will take our recently proposed new type of spin-valley locking (SVL), named C-paired SVL, in antiferromagnetic systems. It directly connects the spin/valley space with the real space, and hence enables both static and dynamical controls of spin and valley to realize a multifunctional antiferromagnetic material. The new emergent quantum degree of freedom in the C-paired SVL is comprised of spin-polarized valleys related by a crystal symmetry instead of the time-reversal symmetry. Thus, both spin and valley can be accessed by simply breaking the corresponding crystal symmetry. Typically, one can use a strain field to induce a large net valley polarization/magnetization and use a charge current to generate a large noncollinear spin current. We predict the realization of the C-paired SVL in monolayer V2Se2O, which indeed exhibits giant piezomagnetism and can generate a large transverse spin current. Based on symmetry analysis and first-principles calculations, we also found C-paired SVL can exist in the following experimentally verified AFM materials, NaOsO3, LaMnO3, LaCrO3, TbFeO3, MnTe, RuO2, MnF2, FeF2, CoF2, and NiF2. All these predicted phenomena have been confirmed in recent experiments in RuO2 and MnTe. Our findings provide new opportunities to integrate various controls of spin and valley with nonvolatile information storage in a single material, which is highly desirable for versatile fundamental research and device applications.

Reference: Nature Communications 12, 2846 (2021)

简历：

Prof. Liu obtained his Bachelor of Science from Xi'an Jiaotong University in 2009 and PhD from Tsinghua University in 2014. After spending three years for his postdoctoral research work in MIT, Prof. Liu then joined the Department of Physics in HKUST in 2017. With his collaborators, Prof. Liu has made the following progresses in the past several years, and he even received the award “National Natural Science Foundation of China Excellent Young Scientist 2020”.

Prof. Liu has a very broad interest in condensed matter physics and quantum physics, varying from the traditional phenomena like ferroelectricity to the exotic topological phases like quantum spin Hall insulators. Currently, his research focuses on two parts: 1) explore new phase of quantum matter including both symmetry-breaking phases and topological phases, and their novel properties, material realizations, experimental signatures and potential applications; 2) combination of advanced machine learning techniques and quantum physics, especially the combination of machine learning techniques and quantum Monte Carlo simulations and all optical neural networks.

联系方式：ygyao@bit.edu.cn

邀请人： 姚裕贵 教授

网 址：http://physics.bit.edu.cn/

承办单位：物理学院、先进光电量子结构设计与测量教育部重点实验室