1
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Mishra SS, Lourembam J, Lin DJX, Singh R. Active ballistic orbital transport in Ni/Pt heterostructure. Nat Commun 2024; 15:4568. [PMID: 38811558 PMCID: PMC11137139 DOI: 10.1038/s41467-024-48891-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2024] [Accepted: 05/15/2024] [Indexed: 05/31/2024] Open
Abstract
Orbital current, defined as the orbital character of Bloch states in solids, can travel with larger coherence length through a broader range of materials than its spin counterpart, facilitating a robust, higher density and energy efficient information transmission. Hence, active control of orbital transport plays a pivotal role in the progress of the evolving field of quantum information technology. Unlike spin angular momentum, orbital angular momentum couples to phonon angular momentum efficiently via orbital-crystal momentum (L-k) coupling, allowing us to control orbital transport through crystal field potential mediated angular momentum transfer. Here, leveraging the orbital dependant efficient L-k coupling, we have experimentally demonstrated the active control of orbital current velocity in Ni/Pt heterostructure. We observe terahertz emission from Ni/Pt heterostructure via long-range ballistic orbital transport, as evidenced by the delay, and chirping in the emitted THz pulse correlating with increased Pt thickness. Additionally, we also have identified a critical energy density required to overcome collisions in orbital transport, enabling a swifter flow of orbital current. Femtosecond light driven active control of the ballistic orbital transport lays the foundation for the development of dynamic optorbitronics for transmitting information over extended distance.
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Affiliation(s)
- Sobhan Subhra Mishra
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore
- Centre for Disruptive Photonic Technologies, The Photonics Institute, Nanyang Technological University, Singapore, 639798, Singapore
| | - James Lourembam
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, Singapore, 138364, Singapore
| | - Dennis Jing Xiong Lin
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, Singapore, 138364, Singapore
| | - Ranjan Singh
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore.
- Centre for Disruptive Photonic Technologies, The Photonics Institute, Nanyang Technological University, Singapore, 639798, Singapore.
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2
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Li R, Zou X, Chen Z, Feng X, Huang B, Dai Y, Niu C. Floquet engineering of the orbital Hall effect and valleytronics in two-dimensional topological magnets. MATERIALS HORIZONS 2024. [PMID: 38805308 DOI: 10.1039/d4mh00237g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2024]
Abstract
We show that circularly polarized light is a versatile way to manipulate both the orbital Hall effect and band topology in two-dimensional ferromagnets. Employing the hexagonal lattice, we proposed that interactions between light and matter allow for the modulation of the valley polarization effect, and then band inversions, accompanied by the band gap closing and reopening processes, can be achieved subsequently at two valleys. Remarkably, the distribution of orbital angular momentum can be controlled by the band inversions, leading to the Floquet engineering of the orbital Hall effect, as well as the topological phase transition from a second-order topological insulator to a Chern insulator with in-plane magnetization, and then to a normal insulator. Furthermore, first-principles calculations validate the feasibility with the 2H-ScI2 monolayer as a candidate material, paving a technological avenue to bridge the orbitronics and nontrivial topology using Floquet engineering.
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Affiliation(s)
- Runhan Li
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Xiaorong Zou
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Zhiqi Chen
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Xiaoran Feng
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Baibiao Huang
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Ying Dai
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Chengwang Niu
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
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3
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Go G, An D, Lee HW, Kim SK. Magnon Orbital Nernst Effect in Honeycomb Antiferromagnets without Spin-Orbit Coupling. NANO LETTERS 2024; 24:5968-5974. [PMID: 38682941 PMCID: PMC11117403 DOI: 10.1021/acs.nanolett.4c00430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Revised: 04/24/2024] [Accepted: 04/25/2024] [Indexed: 05/01/2024]
Abstract
Recently, topological responses of magnons have emerged as a central theme in magnetism and spintronics. However, resulting Hall responses are typically weak and infrequent, since, according to present understanding, they arise from effective spin-orbit couplings, which are weaker compared to the exchange energy. Here, by investigating transport properties of magnon orbital moments, we predict that the magnon orbital Nernst effect is an intrinsic characteristic of the honeycomb antiferromagnet and therefore, it manifests even in the absence of spin-orbit coupling. For the electric detection, we propose an experimental scheme based on the magnetoelectric effect. Our results break the conventional wisdom that the Hall transport of magnons requires spin-orbit coupling by predicting the magnon orbital Nernst effect in a system without it, which leads us to envision that our work initiates the intensive search for various magnon Hall effects in generic magnetic systems with no reliance on spin-orbit coupling.
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Affiliation(s)
- Gyungchoon Go
- Department
of Physics, Korea Advanced Institute of
Science and Technology, Daejeon 34141, Korea
| | - Daehyeon An
- Department
of Physics, Korea Advanced Institute of
Science and Technology, Daejeon 34141, Korea
| | - Hyun-Woo Lee
- Department
of Physics, Pohang University of Science
and Technology, Pohang 37673, Korea
| | - Se Kwon Kim
- Department
of Physics, Korea Advanced Institute of
Science and Technology, Daejeon 34141, Korea
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4
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Liu H, Culcer D. Dominance of Extrinsic Scattering Mechanisms in the Orbital Hall Effect: Graphene, Transition Metal Dichalcogenides, and Topological Antiferromagnets. PHYSICAL REVIEW LETTERS 2024; 132:186302. [PMID: 38759195 DOI: 10.1103/physrevlett.132.186302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2023] [Revised: 03/06/2024] [Accepted: 04/02/2024] [Indexed: 05/19/2024]
Abstract
The theory of the orbital Hall effect (OHE), a transverse flow of orbital angular momentum (OAM) in response to an electric field, has concentrated on intrinsic mechanisms. Here, using a quantum kinetic formulation, we determine the full OHE in the presence of short-range disorder using 2D massive Dirac fermions as a prototype. We find that, in doped systems, extrinsic effects associated with the Fermi surface (skew scattering and side jump) provide ≈95% of the OHE. This suggests that, at experimentally relevant transport densities, the OHE is primarily extrinsic.
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Affiliation(s)
- Hong Liu
- School of Physics and Australian Research Council Centre of Excellence in Low-Energy Electronics Technologies, UNSW Node, The University of New South Wales, Sydney 2052, Australia
| | - Dimitrie Culcer
- School of Physics and Australian Research Council Centre of Excellence in Low-Energy Electronics Technologies, UNSW Node, The University of New South Wales, Sydney 2052, Australia
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5
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Chen Z, Li R, Bai Y, Mao N, Zeer M, Go D, Dai Y, Huang B, Mokrousov Y, Niu C. Topology-Engineered Orbital Hall Effect in Two-Dimensional Ferromagnets. NANO LETTERS 2024. [PMID: 38619844 DOI: 10.1021/acs.nanolett.3c05129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/16/2024]
Abstract
Recent advances in the manipulation of the orbital angular momentum (OAM) within the paradigm of orbitronics presents a promising avenue for the design of future electronic devices. In this context, the recently observed orbital Hall effect (OHE) occupies a special place. Here, focusing on both the second-order topological and quantum anomalous Hall insulators in two-dimensional ferromagnets, we demonstrate that topological phase transitions present an efficient and straightforward way to engineer the OHE, where the OAM distribution can be controlled by the nature of the band inversion. Using first-principles calculations, we identify Janus RuBrCl and three septuple layers of MnBi2Te4 as experimentally feasible examples of the proposed mechanism of OHE engineering by topology. With our work, we open up new possibilities for innovative applications in topological spintronics and orbitronics.
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Affiliation(s)
- Zhiqi Chen
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
| | - Runhan Li
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
| | - Yingxi Bai
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
| | - Ning Mao
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
| | - Mahmoud Zeer
- Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany
- Department of Physics, RWTH Aachen University, 52056 Aachen, Germany
| | - Dongwook Go
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
| | - Ying Dai
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
| | - Baibiao Huang
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
| | - Yuriy Mokrousov
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
| | - Chengwang Niu
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
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6
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Xu Y, Zhang F, Fert A, Jaffres HY, Liu Y, Xu R, Jiang Y, Cheng H, Zhao W. Orbitronics: light-induced orbital currents in Ni studied by terahertz emission experiments. Nat Commun 2024; 15:2043. [PMID: 38448561 PMCID: PMC10917802 DOI: 10.1038/s41467-024-46405-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2023] [Accepted: 02/26/2024] [Indexed: 03/08/2024] Open
Abstract
Orbitronics is based on the use of orbital currents as information carriers. Orbital currents can be generated from the conversion of charge or spin currents, and inversely, they could be converted back to charge or spin currents. Here we demonstrate that orbital currents can also be generated by femtosecond light pulses on Ni. In multilayers associating Ni with oxides and nonmagnetic metals such as Cu, we detect the orbital currents by their conversion into charge currents and the resulting terahertz emission. We show that the orbital currents extraordinarily predominate the light-induced spin currents in Ni-based systems, whereas only spin currents can be detected with CoFeB-based systems. In addition, the analysis of the time delays of the terahertz pulses leads to relevant information on the velocity and propagation length of orbital carriers. Our finding of light-induced orbital currents and our observation of their conversion into charge currents opens new avenues in orbitronics, including the development of orbitronic terahertz devices.
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Affiliation(s)
- Yong Xu
- National Key Lab of Spintronics, International Innovation Institute, Beihang University, Hangzhou, 311115, China
- Fert Beijing Institute, School of Integrated Circuit Science and Engineering, Beihang University, Beijing, 100191, China
- Hefei Innovation Research Institute, Beihang University, Hefei, 230013, China
| | - Fan Zhang
- Hefei Innovation Research Institute, Beihang University, Hefei, 230013, China
| | - Albert Fert
- Fert Beijing Institute, School of Integrated Circuit Science and Engineering, Beihang University, Beijing, 100191, China.
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, Palaiseau, 91767, France.
| | - Henri-Yves Jaffres
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, Palaiseau, 91767, France
| | - Yongshan Liu
- Fert Beijing Institute, School of Integrated Circuit Science and Engineering, Beihang University, Beijing, 100191, China
- Hefei Innovation Research Institute, Beihang University, Hefei, 230013, China
| | - Renyou Xu
- Fert Beijing Institute, School of Integrated Circuit Science and Engineering, Beihang University, Beijing, 100191, China
- Hefei Innovation Research Institute, Beihang University, Hefei, 230013, China
| | - Yuhao Jiang
- Fert Beijing Institute, School of Integrated Circuit Science and Engineering, Beihang University, Beijing, 100191, China
| | - Houyi Cheng
- Fert Beijing Institute, School of Integrated Circuit Science and Engineering, Beihang University, Beijing, 100191, China
- Hefei Innovation Research Institute, Beihang University, Hefei, 230013, China
| | - Weisheng Zhao
- National Key Lab of Spintronics, International Innovation Institute, Beihang University, Hangzhou, 311115, China.
- Fert Beijing Institute, School of Integrated Circuit Science and Engineering, Beihang University, Beijing, 100191, China.
- Hefei Innovation Research Institute, Beihang University, Hefei, 230013, China.
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7
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Adamantopoulos T, Merte M, Go D, Freimuth F, Blügel S, Mokrousov Y. Orbital Rashba Effect as a Platform for Robust Orbital Photocurrents. PHYSICAL REVIEW LETTERS 2024; 132:076901. [PMID: 38427860 DOI: 10.1103/physrevlett.132.076901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Revised: 07/03/2023] [Accepted: 01/09/2024] [Indexed: 03/03/2024]
Abstract
Orbital current has emerged over the past years as one of the key novel concepts in magnetotransport. Here, we demonstrate that laser pulses can be used to generate large and robust nonrelativistic orbital currents in systems where the inversion symmetry is broken by the orbital Rashba effect. By referring to model and first principles tools, we demonstrate that orbital Rashba effect, accompanied by crystal field splitting, can mediate robust orbital photocurrents without a need for spin-orbit interaction even in metallic systems. We show that such nonrelativistic orbital photocurrents are translated into derivative photocurrents of spin when relativistic effects are taken into account. We thus promote orbital photocurrents as a promising platform for optical generation of currents of angular momentum, and discuss their possible applications.
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Affiliation(s)
- T Adamantopoulos
- Peter Grünberg Institut, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
- Department of Physics, RWTH Aachen University, 52056 Aachen, Germany
| | - M Merte
- Peter Grünberg Institut, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
- Department of Physics, RWTH Aachen University, 52056 Aachen, Germany
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
| | - D Go
- Peter Grünberg Institut, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
| | - F Freimuth
- Peter Grünberg Institut, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
| | - S Blügel
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
| | - Y Mokrousov
- Peter Grünberg Institut, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
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8
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Zheng Z, Zeng T, Zhao T, Shi S, Ren L, Zhang T, Jia L, Gu Y, Xiao R, Zhou H, Zhang Q, Lu J, Wang G, Zhao C, Li H, Tay BK, Chen J. Effective electrical manipulation of a topological antiferromagnet by orbital torques. Nat Commun 2024; 15:745. [PMID: 38272914 PMCID: PMC10811228 DOI: 10.1038/s41467-024-45109-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2023] [Accepted: 01/09/2024] [Indexed: 01/27/2024] Open
Abstract
The electrical control of the non-trivial topology in Weyl antiferromagnets is of great interest for the development of next-generation spintronic devices. Recent studies suggest that the spin Hall effect can switch the topological antiferromagnetic order. However, the switching efficiency remains relatively low. Here, we demonstrate the effective manipulation of antiferromagnetic order in the Weyl semimetal Mn3Sn using orbital torques originating from either metal Mn or oxide CuOx. Although Mn3Sn can convert orbital current to spin current on its own, we find that inserting a heavy metal layer, such as Pt, of appropriate thickness can effectively reduce the critical switching current density by one order of magnitude. In addition, we show that the memristor-like switching behaviour of Mn3Sn can mimic the potentiation and depression processes of a synapse with high linearity-which may be beneficial for constructing accurate artificial neural networks. Our work paves a way for manipulating the topological antiferromagnetic order and may inspire more high-performance antiferromagnetic functional devices.
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Affiliation(s)
- Zhenyi Zheng
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Tao Zeng
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Tieyang Zhao
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Shu Shi
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Lizhu Ren
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Tongtong Zhang
- Centre for Micro- and Nano-Electronics (CMNE), School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore, Singapore
| | - Lanxin Jia
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Youdi Gu
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Rui Xiao
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Hengan Zhou
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Qihan Zhang
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Jiaqi Lu
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
| | - Guilei Wang
- Beijing Superstring Academy of Memory Technology, Beijing, 100176, China
| | - Chao Zhao
- Beijing Superstring Academy of Memory Technology, Beijing, 100176, China
| | - Huihui Li
- Beijing Superstring Academy of Memory Technology, Beijing, 100176, China.
| | - Beng Kang Tay
- Centre for Micro- and Nano-Electronics (CMNE), School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore, Singapore.
| | - Jingsheng Chen
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore.
- Chongqing Research Institute, National University of Singapore, Chongqing, 401120, China.
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9
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Tazai R, Yamakawa Y, Kontani H. Charge-loop current order and Z 3 nematicity mediated by bond order fluctuations in kagome metals. Nat Commun 2023; 14:7845. [PMID: 38030600 PMCID: PMC10687221 DOI: 10.1038/s41467-023-42952-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 10/25/2023] [Indexed: 12/01/2023] Open
Abstract
Recent experiments on geometrically frustrated kagome metal AV3Sb5 (A = K, Rb, Cs) have revealed the emergence of the charge loop current (cLC) order near the bond order (BO) phase. However, the origin of the cLC and its interplay with other phases have been uncovered. Here, we propose a novel mechanism of the cLC state, by focusing on the BO phase common in kagome metals. The BO fluctuations in kagome metals, which emerges due to the Coulomb interaction and the electron-phonon coupling, mediate the odd-parity particle-hole condensation that gives rise to the topological current order. Furthermore, the predicted cLC+BO phase gives rise to the Z3-nematic state in addition to the giant anomalous Hall effect. The present theory predicts the close relationship between the cLC, the BO, and the nematicity, which is significant to understand the cascade of quantum electron states in kagome metals. The present scenario provides a natural understanding.
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Grants
- JP20K22328 Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- JP22K14003 Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- JP19H05825 Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- JP20K03858 Ministry of Education, Culture, Sports, Science and Technology (MEXT)
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Affiliation(s)
- Rina Tazai
- Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, 606-8502, Japan.
| | - Youichi Yamakawa
- Department of Physics, Nagoya University, Furo-cho, Nagoya, 464-8602, Japan
| | - Hiroshi Kontani
- Department of Physics, Nagoya University, Furo-cho, Nagoya, 464-8602, Japan
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10
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Xie H, Zhang N, Ma Y, Chen X, Ke L, Wu Y. Efficient Noncollinear Antiferromagnetic State Switching Induced by the Orbital Hall Effect in Chromium. NANO LETTERS 2023; 23:10274-10281. [PMID: 37909311 DOI: 10.1021/acs.nanolett.3c02797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2023]
Abstract
Recently, orbital Hall current has attracted attention as an alternative method to switch the magnetization of ferromagnets. Here we present our findings on electrical switching of the antiferromagnetic state in Mn3Sn/Cr, where despite the much smaller spin Hall angle of Cr, the switching current density is comparable to heavy metal-based heterostructures. However, the inverse process, i.e., spin-to-charge conversion in Cr-based heterostructures, is much less efficient than the Pt-based equivalents, as manifested in the 1 order of magnitude smaller terahertz emission intensity and spin current-induced magnetoresistance. These results in combination with the slow decay of terahertz emission against Cr thickness (diffusion length of ∼11 nm) suggest that the observed magnetic switching can be attributed to orbital current generation in Cr, followed by efficient conversion to spin current. Our work demonstrates the potential of light metals like Cr as efficient orbital/spin current sources for antiferromagnetic spintronics.
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Affiliation(s)
- Hang Xie
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
| | - Nan Zhang
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 138634, Singapore
| | - Yuteng Ma
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
- National University of Singapore (Chong Qing) Research Institute, Chongqing Liang Jiang New Area, Chongqing 401123, China
| | - Xin Chen
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
| | - Lin Ke
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 138634, Singapore
| | - Yihong Wu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
- National University of Singapore (Chong Qing) Research Institute, Chongqing Liang Jiang New Area, Chongqing 401123, China
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11
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Cheng Q, Yan Z, Song W, Kong J, Li D, Xu W, Xie Y, Liang X, Zhao Z. Evolution of local edge state braiding and spin topological transport characterization of Te-doped monolayer 1T'-MoS 2. Phys Chem Chem Phys 2023; 25:29633-29640. [PMID: 37880996 DOI: 10.1039/d3cp03566b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2023]
Abstract
We conducted first-principles calculations to investigate the dynamic braiding of local edge states and the spin topological transport mechanism in a strong topological MoS1.75Te0.25 matrix. The presence of type-II Van Hove singularity in the middle of the X-S path indicates a strong cohesive interaction and a paring condensation mechanism within the matrix. The surface state data of MoS1.75Te0.25 clearly demonstrate the characteristic features of strong regular loop braiding in spin transport. The spin Hall conductivity of the matrix was determined from the anisotropic characteristics of the spin Berry curvature. The phase transition of the spin Hall conductivity was evidenced by the positive sign of local spin polarization strength, primarily contributed by the dz2 orbital of Mo atoms, and the negative sign of spin polarization strength, mainly contributed by the p-px orbitals of S atoms. Moreover, the inclusion of Te selectively tuned the spin transport efficiency of the dz2 and px orbitals. Comprehensive braiding and readout of edge states can be achieved using an artificially designed MoS1.75Te0.25 spintronic device. This 2D fractional braiding holds significant potential for applications in topological quantum computation.
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Affiliation(s)
- Qian Cheng
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China.
| | - Zhengxin Yan
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China.
| | - Wei Song
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China.
| | - Juntao Kong
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China.
| | - Dongxin Li
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China.
| | - Wuyue Xu
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China.
| | - You Xie
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China.
| | - Xingkun Liang
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China.
| | - Zehua Zhao
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China.
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12
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Lyalin I, Alikhah S, Berritta M, Oppeneer PM, Kawakami RK. Magneto-Optical Detection of the Orbital Hall Effect in Chromium. PHYSICAL REVIEW LETTERS 2023; 131:156702. [PMID: 37897779 DOI: 10.1103/physrevlett.131.156702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Accepted: 09/07/2023] [Indexed: 10/30/2023]
Abstract
The orbital Hall effect has been theoretically predicted but its direct observation is a challenge. Here, we report the magneto-optical detection of current-induced orbital accumulation at the surface of a light 3d transition metal, Cr. The orbital polarization is in-plane, transverse to the current direction, and scales linearly with current density, consistent with the orbital Hall effect. Comparing the thickness-dependent magneto-optical measurements with ab initio calculations, we estimate an orbital diffusion length in Cr of 6.6±0.6 nm.
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Affiliation(s)
- Igor Lyalin
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Sanaz Alikhah
- Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-75120 Uppsala, Sweden
| | - Marco Berritta
- Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-75120 Uppsala, Sweden
- Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, United Kingdom
| | - Peter M Oppeneer
- Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-75120 Uppsala, Sweden
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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13
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Li T, Liu L, Li X, Zhao X, An H, Ando K. Giant Orbital-to-Spin Conversion for Efficient Current-Induced Magnetization Switching of Ferrimagnetic Insulator. NANO LETTERS 2023; 23:7174-7179. [PMID: 37466330 DOI: 10.1021/acs.nanolett.3c02104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2023]
Abstract
It has long been believed that the attachment of two heavy metals such as Ta and Pt with opposite spin Hall angles results in a weakened net torque generation efficiency in magnetization switching devices. Here, we report a giant orbital-to-spin conversion in Ta/Pt/Tm3Fe5O12 (TmIG) heterostructures. We show that the torque generation efficiency is enhanced by an order of magnitude in the Ta/Pt/TmIG trilayer compared to that in the Pt/TmIG bilayer. This enhancement is further evidenced by the fact that the critical current density for the magnetization switching of the Ta/Pt/TmIG is an order of magnitude smaller than that of the Pt/TmIG. It is found that the orbital current generated from Ta through the orbital Hall effect (OHE) is converted to the spin current in the interior of Pt. Our discovery offers an extraordinary approach to enhance the torque generation for magnetization switching of insulators and provides an important piece of information for orbitronics.
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Affiliation(s)
- Tianhui Li
- College of New Materials and New Energies, Shenzhen Technology University, Shenzhen 518118, P. R. China
| | - Long Liu
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P. R. China
| | - Xiaoguang Li
- College of Engineering Physics, Shenzhen Technology University, Shenzhen 518118, P. R. China
| | - Xiaotian Zhao
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P. R. China
| | - Hongyu An
- College of New Materials and New Energies, Shenzhen Technology University, Shenzhen 518118, P. R. China
| | - Kazuya Ando
- Department of Applied Physics and Physico-Informatics, Keio University, Yokohama 223-8522, Japan
- Keio Institute of Pure and Applied Science, Keio University, Yokohama 223-8522, Japan
- Center for Spintronics Research Network, Keio University, Yokohama 223-8522, Japan
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14
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Choi YG, Jo D, Ko KH, Go D, Kim KH, Park HG, Kim C, Min BC, Choi GM, Lee HW. Observation of the orbital Hall effect in a light metal Ti. Nature 2023; 619:52-56. [PMID: 37407680 DOI: 10.1038/s41586-023-06101-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Accepted: 04/19/2023] [Indexed: 07/07/2023]
Abstract
The orbital Hall effect1 refers to the generation of electron orbital angular momentum flow transverse to an external electric field. Contrary to the common belief that the orbital angular momentum is quenched in solids, theoretical studies2,3 predict that the orbital Hall effect can be strong and is a fundamental origin of the spin Hall effect4-7 in many transition metals. Despite the growing circumstantial evidence8-11, its direct detection remains elusive. Here we report the magneto-optical observation of the orbital Hall effect in the light metal titanium (Ti). The Kerr rotation by the orbital magnetic moment accumulated at Ti surfaces owing to the orbital Hall current is measured, and the result agrees with theoretical calculations semi-quantitatively and is supported by the orbital torque12 measurement in Ti-based magnetic heterostructures. This result confirms the orbital Hall effect and indicates that the orbital angular momentum is an important dynamic degree of freedom in solids. Moreover, this calls for renewed studies of the orbital effect on other degrees of freedom such as spin2,3,13,14, valley15,16, phonon17-19 and magnon20,21 dynamics.
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Affiliation(s)
- Young-Gwan Choi
- Department of Energy Science, Sungkyunkwan University, Suwon, Korea
| | - Daegeun Jo
- Department of Physics, Pohang University of Science and Technology, Pohang, Korea
| | - Kyung-Hun Ko
- Department of Energy Science, Sungkyunkwan University, Suwon, Korea
| | - Dongwook Go
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, Julich, Germany
- Institute of Physics, Johannes Gutenberg University Mainz, Mainz, Germany
| | - Kyung-Han Kim
- Department of Physics, Pohang University of Science and Technology, Pohang, Korea
| | - Hee Gyum Park
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, Korea
| | - Changyoung Kim
- Department of Physics and Astronomy, Seoul National University, Seoul, Korea
- Center for Correlated Electron Systems, Institute for Basic Science, Seoul, Korea
| | - Byoung-Chul Min
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, Korea
| | - Gyung-Min Choi
- Department of Energy Science, Sungkyunkwan University, Suwon, Korea.
- Center for Integrated Nanostructure Physics, Institute for Basic Science, Suwon, Korea.
| | - Hyun-Woo Lee
- Department of Physics, Pohang University of Science and Technology, Pohang, Korea.
- Asia Pacific Center for Theoretical Physics, Pohang, Korea.
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15
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Go D, Jo D, Kim KW, Lee S, Kang MG, Park BG, Blügel S, Lee HW, Mokrousov Y. Long-Range Orbital Torque by Momentum-Space Hotspots. PHYSICAL REVIEW LETTERS 2023; 130:246701. [PMID: 37390424 DOI: 10.1103/physrevlett.130.246701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 05/16/2022] [Accepted: 05/16/2023] [Indexed: 07/02/2023]
Abstract
While it is often assumed that the orbital response is suppressed and short ranged due to strong crystal field potential and orbital quenching, we show that the orbital response can be remarkably long ranged in ferromagnets. In a bilayer consisting of a nonmagnet and a ferromagnet, spin injection from the interface results in spin accumulation and torque in the ferromagnet, which rapidly oscillate and decay by spin dephasing. In contrast, even when an external electric field is applied only on the nonmagnet, we find substantially long-ranged induced orbital angular momentum in the ferromagnet, which can go far beyond the spin dephasing length. This unusual feature is attributed to nearly degenerate orbital characters imposed by the crystal symmetry, which form hotspots for the intrinsic orbital response. Because only the states near the hotspots contribute dominantly, the induced orbital angular momentum does not exhibit destructive interference among states with different momentum as in the case of the spin dephasing. This gives rise to a distinct type of orbital torque on the magnetization, increasing with the thickness of the ferromagnet. Such behavior may serve as critical long-sought evidence of orbital transport to be directly tested in experiments. Our findings open the possibility of using long-range orbital response in orbitronic device applications.
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Affiliation(s)
- Dongwook Go
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
| | - Daegeun Jo
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Kyoung-Whan Kim
- Center for Spintronics, Korea Institute of Science and Technology, Seoul 02792, Korea
| | - Soogil Lee
- Department of Materials Science and Engineering and KI for Nanocentury, KAIST, Daejeon 34141, Korea
| | - Min-Gu Kang
- Department of Materials Science and Engineering and KI for Nanocentury, KAIST, Daejeon 34141, Korea
- Department of Materials, ETH Zurich, 8093 Zurich, Switzerland
| | - Byong-Guk Park
- Department of Materials Science and Engineering and KI for Nanocentury, KAIST, Daejeon 34141, Korea
| | - Stefan Blügel
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Hyun-Woo Lee
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Yuriy Mokrousov
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
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16
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Han S, Lee HW, Kim KW. Orbital Dynamics in Centrosymmetric Systems. PHYSICAL REVIEW LETTERS 2022; 128:176601. [PMID: 35570433 DOI: 10.1103/physrevlett.128.176601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Accepted: 04/07/2022] [Indexed: 06/15/2023]
Abstract
Orbital dynamics in time-reversal-symmetric centrosymmetric systems is examined theoretically. Contrary to common belief, we demonstrate that many aspects of orbital dynamics are qualitatively different from spin dynamics because the algebraic properties of the orbital and spin angular momentum operators are different. This difference generates interesting orbital responses, which do not have spin counterparts. For instance, the orbital angular momentum expectation values may oscillate even without breaking neither the time-reversal nor the inversion symmetry. Our quantum Boltzmann approach reproduces the previous result on the orbital Hall effect and reveals additional orbital dynamics phenomena, whose detection schemes are discussed briefly. Our work will be useful for the experimental differentiation of the orbital dynamics from the spin dynamics.
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Affiliation(s)
- Seungyun Han
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Hyun-Woo Lee
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Kyoung-Whan Kim
- Center for Spintronics, Korea Institute of Science and Technology, Seoul 02792, Korea
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17
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Zhu X, Xu Y, Cao C, Shang T, Xie Y, Zhan Q. Recent developments on the magnetic and electrical transport properties of FeRh- and Rh-based heterostructures. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:144004. [PMID: 35026751 DOI: 10.1088/1361-648x/ac4b28] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 01/13/2022] [Indexed: 06/14/2023]
Abstract
It is fascinating how the binary alloy FeRh has been the subject of a vast number of studies almost solely for a single-phase transition. This is, however, reasonable, considering how various degrees of freedom are intertwined around this phase transition. Furthermore, the tunability of this phase transition-the large response to tuning parameters, such as electric field and strain-endows FeRh huge potential in applications. Compared to the bulk counterpart, FeRh in the thin-film form is superior in many aspects: materials in thin-film form are often more technologically relevant in the first place; in addition, the substrates add extra dimensions to the tunability, especially when the substrate itself is multiferroic. Here we review recent developments on the magnetic and transport properties of heterostructures based on FeRh and its end-member Rh, with the latter providing a new route to exploiting spin-orbit interactions in functional spintronic heterostructures other than the more often employed 5dmetals. The methods utilized in the investigation of the physical properties in these systems, and the design principles employed in the engineering thereof may conceivably be extended to similar phase transitions to other magnetic materials.
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Affiliation(s)
- Xiaoyan Zhu
- Key Laboratory of Polar Materials and Devices (MOE), School of Physics and Electronic Science, East China Normal University, Shanghai 200241, People's Republic of China
| | - Yang Xu
- Key Laboratory of Polar Materials and Devices (MOE), School of Physics and Electronic Science, East China Normal University, Shanghai 200241, People's Republic of China
| | - Cuimei Cao
- Key Laboratory of Polar Materials and Devices (MOE), School of Physics and Electronic Science, East China Normal University, Shanghai 200241, People's Republic of China
| | - Tian Shang
- Key Laboratory of Polar Materials and Devices (MOE), School of Physics and Electronic Science, East China Normal University, Shanghai 200241, People's Republic of China
| | - Yali Xie
- Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, People's Republic of China
| | - Qingfeng Zhan
- Key Laboratory of Polar Materials and Devices (MOE), School of Physics and Electronic Science, East China Normal University, Shanghai 200241, People's Republic of China
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18
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Lee D, Go D, Park HJ, Jeong W, Ko HW, Yun D, Jo D, Lee S, Go G, Oh JH, Kim KJ, Park BG, Min BC, Koo HC, Lee HW, Lee O, Lee KJ. Orbital torque in magnetic bilayers. Nat Commun 2021; 12:6710. [PMID: 34795204 PMCID: PMC8602295 DOI: 10.1038/s41467-021-26650-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2021] [Accepted: 10/18/2021] [Indexed: 11/20/2022] Open
Abstract
The orbital Hall effect describes the generation of the orbital current flowing in a perpendicular direction to an external electric field, analogous to the spin Hall effect. As the orbital current carries the angular momentum as the spin current does, injection of the orbital current into a ferromagnet can result in torque on the magnetization, which provides a way to detect the orbital Hall effect. With this motivation, we examine the current-induced spin-orbit torques in various ferromagnet/heavy metal bilayers by theory and experiment. Analysis of the magnetic torque reveals the presence of the contribution from the orbital Hall effect in the heavy metal, which competes with the contribution from the spin Hall effect. In particular, we find that the net torque in Ni/Ta bilayers is opposite in sign to the spin Hall theory prediction but instead consistent with the orbital Hall theory, which unambiguously confirms the orbital torque generated by the orbital Hall effect. Our finding opens a possibility of utilizing the orbital current for spintronic device applications, and it will invigorate researches on spin-orbit-coupled phenomena based on orbital engineering.
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Affiliation(s)
- Dongjoon Lee
- grid.222754.40000 0001 0840 2678KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841 Korea ,grid.35541.360000000121053345Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792 Korea
| | - Dongwook Go
- grid.494742.8Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany ,grid.5802.f0000 0001 1941 7111Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
| | - Hyeon-Jong Park
- grid.222754.40000 0001 0840 2678KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841 Korea
| | - Wonmin Jeong
- grid.35541.360000000121053345Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792 Korea ,grid.222754.40000 0001 0840 2678Department of Materials Science and Engineering, Korea University, Seoul, 02841 Korea
| | - Hye-Won Ko
- grid.37172.300000 0001 2292 0500Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141 Korea
| | - Deokhyun Yun
- grid.35541.360000000121053345Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792 Korea ,grid.222754.40000 0001 0840 2678Department of Electrical Engineering, Korea University, Seoul, 02841 Korea
| | - Daegeun Jo
- grid.49100.3c0000 0001 0742 4007Department of Physics, Pohang University of Science and Technology, Pohang, 37673 Korea
| | - Soogil Lee
- grid.37172.300000 0001 2292 0500Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141 Korea
| | - Gyungchoon Go
- grid.37172.300000 0001 2292 0500Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141 Korea
| | - Jung Hyun Oh
- grid.222754.40000 0001 0840 2678Department of Materials Science and Engineering, Korea University, Seoul, 02841 Korea
| | - Kab-Jin Kim
- grid.37172.300000 0001 2292 0500Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141 Korea
| | - Byong-Guk Park
- grid.37172.300000 0001 2292 0500Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141 Korea
| | - Byoung-Chul Min
- grid.35541.360000000121053345Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792 Korea
| | - Hyun Cheol Koo
- grid.222754.40000 0001 0840 2678KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841 Korea ,grid.35541.360000000121053345Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792 Korea
| | - Hyun-Woo Lee
- Department of Physics, Pohang University of Science and Technology, Pohang, 37673, Korea. .,Asia Pacific Center for Theoretical Physics, Pohang, 37673, Korea.
| | - OukJae Lee
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, Korea.
| | - Kyung-Jin Lee
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Korea.
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19
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Spin-orbit torques in normal metal/Nb/ferromagnet heterostructures. Sci Rep 2021; 11:21081. [PMID: 34702943 PMCID: PMC8548299 DOI: 10.1038/s41598-021-99745-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Accepted: 09/27/2021] [Indexed: 11/08/2022] Open
Abstract
Quantifying the spin–orbit torque (SOT) efficiency with changing the layer thickness is crucial for understanding the physical background of SOT. This study investigates the Nb-thickness-dependent SOT efficiency of two types of layered heterostructures: Ta/Nb/CoFeB and Pt/Nb/CoFeB. We find that the Nb thickness dependence of the SOT efficiency in the two samples is quite different. In the Pt/Nb series, the SOT sign changes according to the thickness variation because Pt and Nb have different spin–orbit coupling signs. We observe the resulting reversal in switching polarity through current-induced SOT switching experiments. However, due to the same spin–orbit coupling signs of Ta and Nb, no such polarity reversal was observed in Ta/Nb series. Further, we extract the spin diffusion length of Nb in each heterostructure. These results provide a systematic understanding of the material- and thickness-dependent SOT characteristics.
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20
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Koo HC, Kim SB, Kim H, Park TE, Choi JW, Kim KW, Go G, Oh JH, Lee DK, Park ES, Hong IS, Lee KJ. Rashba Effect in Functional Spintronic Devices. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e2002117. [PMID: 32930418 DOI: 10.1002/adma.202002117] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 05/28/2020] [Indexed: 06/11/2023]
Abstract
Exploiting spin transport increases the functionality of electronic devices and enables such devices to overcome physical limitations related to speed and power. Utilizing the Rashba effect at the interface of heterostructures provides promising opportunities toward the development of high-performance devices because it enables electrical control of the spin information. Herein, the focus is mainly on progress related to the two most compelling devices that exploit the Rashba effect: spin transistors and spin-orbit torque devices. For spin field-effect transistors, the gate-voltage manipulation of the Rashba effect and subsequent control of the spin precession are discussed, including for all-electric spin field-effect transistors. For spin-orbit torque devices, recent theories and experiments on interface-generated spin current are discussed. The future directions of manipulating the Rashba effect to realize fully integrated spin logic and memory devices are also discussed.
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Affiliation(s)
- Hyun Cheol Koo
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, South Korea
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, South Korea
| | - Seong Been Kim
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, South Korea
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, South Korea
| | - Hansung Kim
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, South Korea
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, South Korea
| | - Tae-Eon Park
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, South Korea
| | - Jun Woo Choi
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, South Korea
| | - Kyoung-Whan Kim
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, South Korea
| | - Gyungchoon Go
- Department of Materials Science and Engineering, Korea University, Seoul, 02841, South Korea
| | - Jung Hyun Oh
- Department of Materials Science and Engineering, Korea University, Seoul, 02841, South Korea
| | - Dong-Kyu Lee
- Department of Materials Science and Engineering, Korea University, Seoul, 02841, South Korea
| | - Eun-Sang Park
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02792, South Korea
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, South Korea
| | - Ik-Sun Hong
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, South Korea
| | - Kyung-Jin Lee
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, South Korea
- Department of Materials Science and Engineering, Korea University, Seoul, 02841, South Korea
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21
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Amin VP, Haney PM, Stiles MD. Interfacial spin-orbit torques. JOURNAL OF APPLIED PHYSICS 2020; 128:10.1063/5.0024019. [PMID: 34121763 PMCID: PMC8194107 DOI: 10.1063/5.0024019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Accepted: 09/30/2020] [Indexed: 06/12/2023]
Abstract
Spin-orbit torques offer a promising mechanism for electrically controlling magnetization dynamics in nanoscale heterostructures. While spin-orbit torques occur predominately at interfaces, the physical mechanisms underlying these torques can originate in both the bulk layers and at interfaces. Classifying spin-orbit torques based on the region that they originate in provides clues as to how to optimize the effect. While most bulk spin-orbit torque contributions are well studied, many of the interfacial contributions allowed by symmetry have yet to be fully explored theoretically and experimentally. To facilitate progress, we review interfacial spin-orbit torques from a semiclassical viewpoint and relate these contributions to recent experimental results. Within the same model, we show the relationship between different interface transport parameters. For charges and spins flowing perpendicular to the interface, interfacial spin-orbit coupling both modifies the mixing conductance of magnetoelectronic circuit theory and gives rise to spin memory loss. For in-plane electric fields, interfacial spin-orbit coupling gives rise to torques described by spin-orbit filtering, spin swapping and precession. In addition, these same interfacial processes generate spin currents that flow into the non-magnetic layer. For in-plane electric fields in trilayer structures, the spin currents generated at the interface between one ferromagnetic layer and the non-magnetic spacer layer can propagate through the non-magnetic layer to produce novel torques on the other ferromagnetic layer.
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Affiliation(s)
- V. P. Amin
- Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - P. M. Haney
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - M. D. Stiles
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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22
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Choi GM, Oh JH, Lee DK, Lee SW, Kim KW, Lim M, Min BC, Lee KJ, Lee HW. Optical spin-orbit torque in heavy metal-ferromagnet heterostructures. Nat Commun 2020; 11:1482. [PMID: 32198358 PMCID: PMC7083953 DOI: 10.1038/s41467-020-15247-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Accepted: 02/21/2020] [Indexed: 11/23/2022] Open
Abstract
Spin current generation through the spin-orbit interaction in non-magnetic materials lies at the heart of spintronics. When the generated spin current is injected to a ferromagnet, it produces spin-orbit torque and manipulates magnetization efficiently. Optically generated spin currents are expected to be superior to their electrical counterparts in terms of the manipulation speed. Here we report optical spin-orbit torques in heavy metal/ferromagnet heterostructures. The strong spin-orbit coupling of heavy metals induces photo-excited carriers to be spin-polarized, and their transport from heavy metals to ferromagnets induces a torque on magnetization. Our results demonstrate that heavy metals can generate spin-orbit torque not only electrically but also optically. It is known that torques can be exerted on spins in a ferromagnet (FM) layer when an in-plane electric current is injected into a heavy metal (HM) layer in contact with the FM layer. Here, the authors demonstrate that torques can be generated without the current injection by shining instead circularly polarized light on the HM.
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Affiliation(s)
- Gyung-Min Choi
- Department of Energy Science, Sungkyunkwan University, Suwon, 16419, Korea. .,Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon, 16419, Korea. .,Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02972, Korea.
| | - Jung Hyun Oh
- Department of Materials Science and Engineering, Korea University, Seoul, 02841, Korea
| | - Dong-Kyu Lee
- Department of Materials Science and Engineering, Korea University, Seoul, 02841, Korea
| | - Seo-Won Lee
- Department of Materials Science and Engineering, Korea University, Seoul, 02841, Korea
| | - Kun Woo Kim
- Center for Theoretical Physics of Complex Systems, Institute for Basic Science (IBS), Daejeon, 34051, Korea
| | - Mijin Lim
- Department of Physics, Pohang University of Science and Technology, Pohang, 37673, Korea
| | - Byoung-Chul Min
- Center for Spintronics, Korea Institute of Science and Technology, Seoul, 02972, Korea
| | - Kyung-Jin Lee
- Department of Materials Science and Engineering, Korea University, Seoul, 02841, Korea. .,KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, Korea.
| | - Hyun-Woo Lee
- Department of Physics, Pohang University of Science and Technology, Pohang, 37673, Korea.
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23
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Go D, Freimuth F, Hanke JP, Xue F, Gomonay O, Lee KJ, Blügel S, Haney PM, Lee HW, Mokrousov Y. Theory of Current-Induced Angular Momentum Transfer Dynamics in Spin-Orbit Coupled Systems. PHYSICAL REVIEW RESEARCH 2020; 2:10.1103/physrevresearch.2.033401. [PMID: 33655217 PMCID: PMC7919697 DOI: 10.1103/physrevresearch.2.033401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Motivated by the importance of understanding various competing mechanisms to the current-induced spin-orbit torque on magnetization in complex magnets, we develop a theory of current-induced spin-orbital coupled dynamics in magnetic heterostructures. The theory describes angular momentum transfer between different degrees of freedom in solids, e.g., the electron orbital and spin, the crystal lattice, and the magnetic order parameter. Based on the continuity equations for the spin and orbital angular momenta, we derive equations of motion that relate spin and orbital current fluxes and torques describing the transfer of angular momentum between different degrees of freedom, achieved in a steady state under an applied external electric field. We then propose a classification scheme for the mechanisms of the current-induced torque in magnetic bilayers. We evaluate the sources of torque using density functional theory, effectively capturing the impact of the electronic structure on these quantities. We apply our formalism to two different magnetic bilayers, Fe/W(110) and Ni/W(110), which are chosen such that the orbital and spin Hall effects in W have opposite sign and the resulting spin- and orbital-mediated torques can compete with each other. We find that while the spin torque arising from the spin Hall effect of W is the dominant mechanism of the current-induced torque in Fe/W(110), the dominant mechanism in Ni/W(110) is the orbital torque originating in the orbital Hall effect of the non-magnetic substrate. Thus the effective spin Hall angles for the total torque are negative and positive in the two systems. Our prediction can be experimentally identified in moderately clean samples, where intrinsic contributions dominate. This clearly demonstrates that our formalism is ideal for studying the angular momentum transfer dynamics in spin-orbit coupled systems as it goes beyond the "spin current picture" by naturally incorporating the spin and orbital degrees of freedom on an equal footing. Our calculations reveal that, in addition to the spin and orbital torque, other contributions such as the interfacial torque and self-induced anomalous torque within the ferromagnet are not negligible in both material systems.
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Affiliation(s)
- Dongwook Go
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
- Basic Science Research Institute, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Frank Freimuth
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Jan-Philipp Hanke
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Fei Xue
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Institute for Research in Electronics and Applied Physics & Maryland Nanocenter, University of Maryland, College Park, MD 20742
| | - Olena Gomonay
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
| | - Kyung-Jin Lee
- Department of Materials Science and Engineering, Korea University, Seoul 02841, Korea
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, Korea
| | - Stefan Blügel
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Paul M. Haney
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Hyun-Woo Lee
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Yuriy Mokrousov
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
- Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
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24
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Phong VT, Addison Z, Ahn S, Min H, Agarwal R, Mele EJ. Optically Controlled Orbitronics on a Triangular Lattice. PHYSICAL REVIEW LETTERS 2019; 123:236403. [PMID: 31868486 DOI: 10.1103/physrevlett.123.236403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 07/09/2019] [Indexed: 06/10/2023]
Abstract
The propagation of electrons in an orbital multiplet dispersing on a lattice can support anomalous transport phenomena deriving from an orbitally induced Berry curvature. In striking contrast to the related situation in graphene, we find that anomalous transport for an L=1 multiplet on the primitive 2D triangular lattice is activated by easily implemented on site and optically tunable potentials. We demonstrate this for dynamics in a Bloch band where point degeneracies carrying opposite winding numbers are generically offset in energy, allowing both an anomalous charge Hall conductance with the sign selected by off-resonance coupling to circularly polarized light and a related anomalous orbital Hall conductance activated by layer buckling.
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Affiliation(s)
- Võ Tiến Phong
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Zachariah Addison
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Seongjin Ahn
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, South Korea
| | - Hongki Min
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, South Korea
| | - Ritesh Agarwal
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - E J Mele
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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25
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Crasto de Lima F, Ferreira GJ, Miwa RH. Orbital Pseudospin-Momentum Locking in Two-Dimensional Chiral Borophene. NANO LETTERS 2019; 19:6564-6568. [PMID: 31424949 DOI: 10.1021/acs.nanolett.9b02802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Recently, orbital-textures have been found in Rashba and topological insulator (TI) surface states as a result of the spin-orbit coupling (SOC). Here, we predict a px/py orbital texture, in linear dispersive Dirac bands, arising at the K/K' points of χ-h0 borophene chiral monolayer. Combining "first-principles" calculations with effective Hamiltonians, we show that the orbital pseudospin has its direction locked with the momentum in a similar way as TIs' spin-textures. Additionally, considering a layer pseudospin degree of freedom, this lattice allows stackings of layers with equivalent or opposite chiralities. In turn, we show a control of the orbital textures and layer localization through the designed stacking and external electric field. For instance, for the opposite chirality stacking, the electric field allows for an on/off switch of the orbital-textured Dirac cone.
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Affiliation(s)
- F Crasto de Lima
- Instituto de Física , Universidade Federal de Uberlândia , C.P. 593, 38400-902 , Uberlândia , MG Brazil
| | - G J Ferreira
- Instituto de Física , Universidade Federal de Uberlândia , C.P. 593, 38400-902 , Uberlândia , MG Brazil
| | - R H Miwa
- Instituto de Física , Universidade Federal de Uberlândia , C.P. 593, 38400-902 , Uberlândia , MG Brazil
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26
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Go D, Jo D, Kim C, Lee HW. Intrinsic Spin and Orbital Hall Effects from Orbital Texture. PHYSICAL REVIEW LETTERS 2018; 121:086602. [PMID: 30192574 DOI: 10.1103/physrevlett.121.086602] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2018] [Revised: 07/11/2018] [Indexed: 06/08/2023]
Abstract
We show theoretically that both the intrinsic spin Hall effect (SHE) and orbital Hall effect (OHE) can arise in centrosymmetric systems through momentum-space orbital texture, which is ubiquitous even in centrosymmetric systems unlike spin texture. The OHE occurs even without spin-orbit coupling (SOC) and is converted into the SHE through SOC. The resulting spin Hall conductivity is large (comparable to that of Pt) but depends on the SOC strength in a nonmonotonic way. This mechanism is stable against orbital quenching. This work suggests a path for an ongoing search for materials with stronger SHE. It also calls for experimental efforts to probe orbital degrees of freedom in the OHE and SHE. Possible ways for experimental detection are briefly discussed.
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Affiliation(s)
- Dongwook Go
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Daegeun Jo
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Changyoung Kim
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea
- Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea
| | - Hyun-Woo Lee
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
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27
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Dushenko S, Hokazono M, Nakamura K, Ando Y, Shinjo T, Shiraishi M. Tunable inverse spin Hall effect in nanometer-thick platinum films by ionic gating. Nat Commun 2018; 9:3118. [PMID: 30087340 PMCID: PMC6081370 DOI: 10.1038/s41467-018-05611-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 07/16/2018] [Indexed: 11/29/2022] Open
Abstract
Electric gating can strongly modulate a wide variety of physical properties in semiconductors and insulators, such as significant changes of conductivity in silicon, appearance of superconductivity in SrTiO3, the paramagnet–ferromagnet transition in (In,Mn)As, and so on. The key to such modulation is charge accumulation in solids. Thus, it has been believed that such modulation is out of reach for conventional metals where the number of carriers is too large. However, success in tuning the Curie temperature of ultrathin cobalt gave hope of finally achieving such a degree of control even in metallic materials. Here, we show reversible modulation of up to two orders of magnitude of the inverse spin Hall effect—a phenomenon that governs interconversion between spin and charge currents—in ultrathin platinum. Spin-to-charge conversion enables the generation and use of electric and spin currents in the same device, which is crucial for the future of spintronics and electronics. The ability to electrically control spintronic materials significantly widens their potential for integration into devices, but it is difficult to achieve in metals with high carrier densities. Here the authors demonstrate ionic liquid gated control of the inverse spin Hall effect in platinum.
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Affiliation(s)
- Sergey Dushenko
- Department of Electronic Science and Engineering, Kyoto University, Kyoto, 615-8510, Japan.
| | - Masaya Hokazono
- Department of Electronic Science and Engineering, Kyoto University, Kyoto, 615-8510, Japan
| | - Kohji Nakamura
- Department of Physics Engineering, Mie University, Mie, 514-8507, Japan
| | - Yuichiro Ando
- Department of Electronic Science and Engineering, Kyoto University, Kyoto, 615-8510, Japan
| | - Teruya Shinjo
- Department of Electronic Science and Engineering, Kyoto University, Kyoto, 615-8510, Japan
| | - Masashi Shiraishi
- Department of Electronic Science and Engineering, Kyoto University, Kyoto, 615-8510, Japan.
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28
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Qiu HS, Kato K, Hirota K, Sarukura N, Yoshimura M, Nakajima M. Layer thickness dependence of the terahertz emission based on spin current in ferromagnetic heterostructures. OPTICS EXPRESS 2018; 26:15247-15254. [PMID: 30114774 DOI: 10.1364/oe.26.015247] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 05/27/2018] [Indexed: 06/08/2023]
Abstract
The emission with a bandwidth of 1.5 terahertz based on the spin current in the ferromagnetic heterostructure Co/Pt is demonstrated. The spin transient launched by the NIR femtosecond laser pulse in the Co/Pt is converted into the in-plane charge current due to the inverse spin Hall effect, which gives rise to the terahertz emission towards free space. The dependence of the terahertz emission on the Pt-layer thickness is investigated. To optimize the geometry structure of the new type of emitter, we developed the theoretical model by carefully analyzing the spin transport. Our model reveals the importance to take into account the interfacial spin loss. It can be used to analyze more complex heterostructures.
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29
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Theory of Large Intrinsic Spin Hall Effect in Iridate Semimetals. Sci Rep 2018; 8:8052. [PMID: 29795233 PMCID: PMC5966394 DOI: 10.1038/s41598-018-26355-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 05/08/2018] [Indexed: 11/08/2022] Open
Abstract
We theoretically investigate the mechanism to generate large intrinsic spin Hall effect in iridates or more broadly in 5d transition metal oxides with strong spin-orbit coupling. We demonstrate such a possibility by taking the example of orthorhombic perovskite iridate with nonsymmorphic lattice symmetry, SrIrO3, which is a three-dimensional semimetal with nodal line spectrum. It is shown that large intrinsic spin Hall effect arises in this system via the spin-Berry curvature originating from the nearly degenerate electronic spectra surrounding the nodal line. This effect exists even when the nodal line is gently gapped out, due to the persistent nearly degenerate electronic structure. The magnitude of the spin Hall conductivity is shown to be comparable to the best known example such as doped topological insulators and the biggest in any transition metal oxides. To gain further insight, we compute the intrinsic spin Hall conductivity in both bulk and thin film systems. We find that the geometric confinement in thin films leads to significant modifications of the electronic states, leading to even bigger spin Hall conductivity in certain cases. We compare our findings with the recent experimental report on the discovery of large spin Hall effect in SrIrO3 thin films.
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30
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Freeman R, Zholud A, Dun Z, Zhou H, Urazhdin S. Evidence for Dyakonov-Perel-like Spin Relaxation in Pt. PHYSICAL REVIEW LETTERS 2018; 120:067204. [PMID: 29481219 DOI: 10.1103/physrevlett.120.067204] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 10/30/2017] [Indexed: 06/08/2023]
Abstract
We utilize nanoscale spin valves with Pt spacer layers to characterize spin relaxation in Pt. Analysis of the spin lifetime indicates that Elliott-Yafet spin scattering is dominant at room temperature, but an unexpected intrinsic Dyakonov-Perel-like spin relaxation becomes dominant at cryogenic temperatures. We also observe suppression of spin relaxation in a Pt layer interfaced with a ferromagnet, likely caused by the competition between the effective exchange and spin-orbit fields.
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Affiliation(s)
- Ryan Freeman
- Department of Physics, Emory University, Atlanta, Georgia 30322, USA
| | - Andrei Zholud
- Department of Physics, Emory University, Atlanta, Georgia 30322, USA
| | - Zhiling Dun
- Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Haidong Zhou
- Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Sergei Urazhdin
- Department of Physics, Emory University, Atlanta, Georgia 30322, USA
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31
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Go D, Hanke JP, Buhl PM, Freimuth F, Bihlmayer G, Lee HW, Mokrousov Y, Blügel S. Toward surface orbitronics: giant orbital magnetism from the orbital Rashba effect at the surface of sp-metals. Sci Rep 2017; 7:46742. [PMID: 28440289 PMCID: PMC5404270 DOI: 10.1038/srep46742] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 03/27/2017] [Indexed: 11/09/2022] Open
Abstract
As the inversion symmetry is broken at a surface, spin-orbit interaction gives rise to spin-dependent energy shifts - a phenomenon which is known as the spin Rashba effect. Recently, it has been recognized that an orbital counterpart of the spin Rashba effect - the orbital Rashba effect - can be realized at surfaces even without spin-orbit coupling. Here, we propose a mechanism for the orbital Rashba effect based on sp orbital hybridization, which ultimately leads to the electric polarization of surface states. For the experimentally well-studied system of a BiAg2 monolayer, as a proof of principle, we show from first principles that this effect leads to chiral orbital textures in k-space. In predicting the magnitude of the orbital moment arising from the orbital Rashba effect, we demonstrate the crucial role played by the Berry phase theory for the magnitude and variation of the orbital textures. As a result, we predict a pronounced manifestation of various orbital effects at surfaces, and proclaim the orbital Rashba effect to be a key platform for surface orbitronics.
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Affiliation(s)
- Dongwook Go
- Peter Grünberg Institut and Institute of Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany.,Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Jan-Philipp Hanke
- Peter Grünberg Institut and Institute of Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Patrick M Buhl
- Peter Grünberg Institut and Institute of Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Frank Freimuth
- Peter Grünberg Institut and Institute of Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Gustav Bihlmayer
- Peter Grünberg Institut and Institute of Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Hyun-Woo Lee
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Yuriy Mokrousov
- Peter Grünberg Institut and Institute of Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Stefan Blügel
- Peter Grünberg Institut and Institute of Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
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32
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Weiler M, Shaw JM, Nembach HT, Silva TJ. Phase-sensitive detection of spin pumping via the ac inverse spin Hall effect. PHYSICAL REVIEW LETTERS 2014; 113:157204. [PMID: 25375738 DOI: 10.1103/physrevlett.113.157204] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Indexed: 06/04/2023]
Abstract
We use a phase-sensitive, quantitative technique to separate inductive and ac inverse spin Hall effect (ISHE) voltages observed in Ni(81)Fe(19)/normal metal multilayers under the condition of ferromagnetic resonance. For Ni(81)Fe(19)/Pt thin film bilayers and at microwave frequencies from 7 to 20 GHz, we observe an ac ISHE magnitude that is much larger than that expected from the dc spin Hall angle Θ(SH)(Pt) = 0.1. Furthermore, at these frequencies, we find an unexpected, ≈ 110° phase of the ac ISHE signal relative to the in-plane component of the resonant magnetization precession. We attribute our findings to a dominant intrinsic ac ISHE in Pt.
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Affiliation(s)
- Mathias Weiler
- Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA
| | - Justin M Shaw
- Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA
| | - Hans T Nembach
- Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA
| | - Thomas J Silva
- Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA
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33
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Current-induced spin polarization on metal surfaces probed by spin-polarized positron beam. Sci Rep 2014; 4:4844. [PMID: 24776781 PMCID: PMC4003475 DOI: 10.1038/srep04844] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Accepted: 04/10/2014] [Indexed: 11/09/2022] Open
Abstract
Current-induced spin polarization (CISP) on the outermost surfaces of Au, Cu, Pt, Pd, Ta, and W nanoscaled films were studied using a spin-polarized positron beam. The Au and Cu surfaces showed no significant CISP. In contrast, the Pt, Pd, Ta, and W films exhibited large CISP (3~15% per input charge current of 105 A/cm2) and the CISP of Ta and W were opposite to those of Pt and Pd. The sign of the CISP obeys the same rule in spin Hall effect suggesting that the spin-orbit coupling is mainly responsible for the CISP. The magnitude of the CISP is explained by the Rashba-Edelstein mechanism rather than the diffusive spin Hall effect. This settles a controversy, that which of these two mechanisms dominates the large CISP on metal surfaces.
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34
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Niimi Y, Morota M, Wei DH, Deranlot C, Basletic M, Hamzic A, Fert A, Otani Y. Extrinsic spin Hall effect induced by iridium impurities in copper. PHYSICAL REVIEW LETTERS 2011; 106:126601. [PMID: 21517335 DOI: 10.1103/physrevlett.106.126601] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Indexed: 05/30/2023]
Abstract
We study the extrinsic spin Hall effect induced by Ir impurities in Cu by injecting a pure spin current into a CuIr wire from a lateral spin valve structure. While no spin Hall effect is observed without Ir impurity, the spin Hall resistivity of CuIr increases linearly with the impurity concentration. The spin Hall angle of CuIr, (2.1±0.6)% throughout the concentration range between 1% and 12%, is practically independent of temperature. These results represent a clear example of predominant skew scattering extrinsic contribution to the spin Hall effect in a nonmagnetic alloy.
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Affiliation(s)
- Y Niimi
- Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa, Chiba 277-8581, Japan.
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35
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Freimuth F, Blügel S, Mokrousov Y. Anisotropic spin Hall effect from first principles. PHYSICAL REVIEW LETTERS 2010; 105:246602. [PMID: 21231542 DOI: 10.1103/physrevlett.105.246602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2010] [Indexed: 05/30/2023]
Abstract
We report on first principles calculations of the anisotropy of the intrinsic spin Hall conductivity (SHC) in nonmagnetic hcp metals and in antiferromagnetic Cr. For most of the metals of this study we find large anisotropies. We derive the general relation between the SHC vector and the direction of spin polarization and discuss its consequences for hcp metals. Especially, it is predicted that for systems where the SHC changes sign due to the anisotropy the spin Hall effect may be tuned such that the spin polarization is parallel either to the electric field or to the spin current.
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Affiliation(s)
- Frank Freimuth
- Institut für Festkörperforschung and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
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36
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Kontani H, Goryo J, Hirashima DS. Intrinsic spin Hall Effect in the s-wave superconducting state: analysis of the Rashba model. PHYSICAL REVIEW LETTERS 2009; 102:086602. [PMID: 19257764 DOI: 10.1103/physrevlett.102.086602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2008] [Indexed: 05/27/2023]
Abstract
A general expression for spin Hall conductivity (SHC) in the s-wave superconducting state at finite temperatures is derived. Based on the expression, we study SHC in a two-dimensional electron gas model in the presence of Rashba spin-orbit interaction (SOI). SHC is zero in the normal state, whereas it takes a large negative value as soon as the superconductivity occurs, due to the change in the quasiparticle contributions. Since this remarkable behavior is independent of the strength of the SOI, it will be widely observed in thin films of superconductors with surface-induced Rashba SOI, or in various noncentrosymmetric superconductors.
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Affiliation(s)
- H Kontani
- Department of Physics, Nagoya University, Furo-cho, Nagoya 464-8602, Japan
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