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Xue Q, Sun Y, Zhou J. Nonlinear Optics-Driven Spin Reorientation in Ferromagnetic Materials. ACS NANO 2024. [PMID: 39172468 DOI: 10.1021/acsnano.4c06453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/23/2024]
Abstract
Based on nonlinear optics, we propose that light irradiation could induce a nonequilibrium steady state magnetization variation. We formulize a band theory to elucidate its general microscopic mechanisms, which are rooted by the quantum geometric structure and topological nature of electronic Bloch wave functions. The existence is determined by the light polarization and specific material symmetry, based on the magnetic group theory. In general, for a magnetic system, both circularly and linearly polarized light could exert an effective magnetic field and a magnetic "velocity" (magnetization variation rate over time, serving as an effective torque) to reorient the magnetization direction. They are contributed by spin and orbital angular momenta simultaneously. Aided by group theory and first-principles calculations, we illustrate this theory using a showcase example of monolayer NiCl2, showing that light irradiation effectively generates an out-of-plane effective magnetic torque, which lifts its in-plane easy magnetization. According to magnetic dynamic simulations, under light with a modest intensity, this switching could occur on the order of 0.1-1 ns time scale, demonstrating its ultrafast nature that is desirable for quantum manipulation.
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Affiliation(s)
- Qianqian Xue
- Center for Alloy Innovation and Design, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China
| | - Yan Sun
- Center for Alloy Innovation and Design, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China
| | - Jian Zhou
- Center for Alloy Innovation and Design, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China
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Li J, Zhang A, Liu Y, Liu Q. Group Theory on Quasisymmetry and Protected Near Degeneracy. PHYSICAL REVIEW LETTERS 2024; 133:026402. [PMID: 39073939 DOI: 10.1103/physrevlett.133.026402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Accepted: 05/23/2024] [Indexed: 07/31/2024]
Abstract
In solid state systems, group representation theory is powerful in characterizing the behavior of quasiparticles, notably the energy degeneracy. While conventional group theory is effective in answering yes-or-no questions related to symmetry breaking, its application to determining the magnitude of energy splitting resulting from symmetry lowering is limited. Here, we propose a theory on quasisymmetry and near degeneracy, thereby expanding the applicability of group theory to address questions regarding large-or-small energy splitting. Defined within the degenerate subspace of an unperturbed Hamiltonian, quasisymmetries form an enlarged symmetry group eliminating the first-order splitting. This framework ensures that the magnitude of splitting arises as a second-order effect of symmetry-lowering perturbations, such as external fields and spin-orbit coupling. We systematically tabulate the quasisymmetry groups within 32 crystallographic point groups and find all the possible unitary quasisymmetry group structures regarding double degeneracy. Applying our theory to the realistic material AgLa, we predict a "quasi-Dirac semimetal" phase characterized by two tiny-gap band anticrossings.
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Zheng H, Zhai D, Xiao C, Yao W. Interlayer Electric Multipoles Induced by In-Plane Field from Quantum Geometric Origins. NANO LETTERS 2024; 24:8017-8023. [PMID: 38899935 DOI: 10.1021/acs.nanolett.4c01657] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/21/2024]
Abstract
We show that interlayer charge transfer in 2D materials can be driven by an in-plane electric field, giving rise to electrical multipole generation in linear and second order in-plane field. The linear and nonlinear effects have quantum geometric origins in the Berry curvature and quantum metric, respectively, defined in extended parameter spaces characteristic of layered materials. We elucidate their symmetry characters and demonstrate sizable dipole and quadrupole polarizations, respectively, in twisted bilayers and trilayers of transition metal dichalcogenides. Furthermore, we show that this effect is strongly enhanced during the topological phase transition tuned by interlayer translation. The effects point to a new electric control on the layer quantum degree of freedom.
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Affiliation(s)
- Huiyuan Zheng
- New Cornerstone Science Laboratory, Department of Physics, The University of Hong Kong, Hong Kong, China
- HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong, Hong Kong, China
| | - Dawei Zhai
- New Cornerstone Science Laboratory, Department of Physics, The University of Hong Kong, Hong Kong, China
- HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong, Hong Kong, China
| | - Cong Xiao
- HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong, Hong Kong, China
- Institute of Applied Physics and Materials Engineering, University of Macau, Taipa, Macau, China
| | - Wang Yao
- New Cornerstone Science Laboratory, Department of Physics, The University of Hong Kong, Hong Kong, China
- HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong, Hong Kong, China
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Tang J, Cheng R. Lossless Spin-Orbit Torque in Antiferromagnetic Topological Insulator MnBi_{2}Te_{4}. PHYSICAL REVIEW LETTERS 2024; 132:136701. [PMID: 38613287 DOI: 10.1103/physrevlett.132.136701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2023] [Revised: 08/22/2023] [Accepted: 02/23/2024] [Indexed: 04/14/2024]
Abstract
We formulate and quantify the spin-orbit torque (SOT) in intrinsic antiferromagnetic topological insulator MnBi_{2}Te_{4} of a few septuple-layer thick in charge-neutral condition, which exhibits pronounced layer-resolved characteristics and even-odd contrast. Contrary to traditional current-induced torques, our SOT is not accompanied by Ohm's currents, thus being devoid of Joule heating. We study the SOT-induced magnetic resonances, where in the tri-septuple-layer case we identify a peculiar exchange mode that is blind to microwaves but can be exclusively driven by the predicted SOT. As an inverse effect, the dynamical magnetic moments generate a pure adiabatic current, which occurs concomitantly with the SOT and gives rise to an overall reactance for the MnBi_{2}Te_{4}, enabling a lossless conversion of electric power into magnetic dynamics.
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Affiliation(s)
- Junyu Tang
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - Ran Cheng
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
- Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA
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Xiao C, Wu W, Wang H, Huang YX, Feng X, Liu H, Guo GY, Niu Q, Yang SA. Time-Reversal-Even Nonlinear Current Induced Spin Polarization. PHYSICAL REVIEW LETTERS 2023; 130:166302. [PMID: 37154629 DOI: 10.1103/physrevlett.130.166302] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2022] [Accepted: 03/23/2023] [Indexed: 05/10/2023]
Abstract
We propose a time-reversal-even spin generation in second order of electric fields, which dominates the current induced spin polarization in a wide class of centrosymmetric nonmagnetic materials, and leads to a novel nonlinear spin-orbit torque in magnets. We reveal a quantum origin of this effect from the momentum space dipole of the anomalous spin polarizability. First-principles calculations predict sizable spin generations in several nonmagnetic hcp metals, in monolayer TiTe_{2}, and in ferromagnetic monolayer MnSe_{2}, which can be detected in experiment. Our work opens up the broad vista of nonlinear spintronics in both nonmagnetic and magnetic systems.
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Affiliation(s)
- Cong Xiao
- Department of Physics, The University of Hong Kong, Hong Kong, People's Republic of China
- HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong, Hong Kong, China
| | - Weikang Wu
- Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061, People's Republic of China
| | - Hui Wang
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
| | - Yue-Xin Huang
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
| | - Xiaolong Feng
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
| | - Huiying Liu
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
- School of Physics, Beihang University, Beijing 100191, China
| | - Guang-Yu Guo
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan, Republic of China
- Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan, Republic of China
| | - Qian Niu
- School of Physics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
| | - Shengyuan A Yang
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
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