Altermagnet? Novel properties from the C-paired spin-valley locking
by
TDLI Meeting Room N499
Abstract
Antiferromagnetic (AFM) materials hold great promises in the next-generation information technology due to the zero stray field and ultra-fast dynamics, and how to detect and manipulate the AFM orders been becoming one of the bottlenecks. In this talk, I will present our works about our recently proposed new type of spin-valley locking (SVL), named C-paired SVL, which enables both static and dynamical controls of AFMs to realize a multifunctional antiferromagnetic material. Compared to the spin structure of 2D materials and the surface states of topological materials, C-paired SVL is enabled by a crystal symmetry instead of the time-reversal symmetry, and the large spin splitting is from the exchange coupling between itinerant electrons and local magnetic moments instead of spin-orbit coupling. 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. Based on symmetry analysis and first-principles calculations, we also predicted C-paired SVL can exist in V2Se2O, V2Te2O, MnTe, RuO2, MnF2, NaOsO3, LaMnO3, LaCrO3, TbFeO3, FeF2, CoF2, NiF2, etc. All these predicted phenomena have been confirmed in recent experiments in RbV2Te2O, RuO2 and MnTe [Nat. Commun. 12, 2846 (2021)]. These properties can also help us realize the electric readout and 180o deterministic switching of the Néel order, which has also been confirmed in our recent experimental work [Sci. Adv. 10, eadn0479 (2024)]. Due to the unique properties distinct from conventional ferromagnet and antiferromagnet, these materials were proposed to belong to a third type of magnets, named altermagnet in 2022 [Phys. Rev. X 12, 040501 (2022)]
Biography
Prof. Junwei Liu obtained his PhD in the department of physics, Tsinghua University, in 2014, and then he started his postdoctoral research in Massachusetts Institute of Technology. He joined Hong Kong University of Science and Technology in 2017 as an assistant professor (https://iascqt.hkust.edu.hk/junwei-liu) and was promoted to an associate professor in 2023.
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.
Division
Condensed Matter
Other information
Tencent Meeting link: https://meeting.tencent.com/dm/mQvLyeNTFlJd
Meeting ID: 708 672 757, no password.
