1
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Watanabe H, Yanase Y. Magnetic parity violation and parity-time-reversal-symmetric magnets. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:373001. [PMID: 38899401 DOI: 10.1088/1361-648x/ad52dd] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2024] [Accepted: 05/31/2024] [Indexed: 06/21/2024]
Abstract
Parity-time-reversal symmetry (PTsymmetry), a symmetry for the combined operations of space inversion (P) and time reversal (T), is a fundamental concept of physics and characterizes the functionality of materials as well asPandTsymmetries. In particular, thePT-symmetric systems can be found in the centrosymmetric crystals undergoing the parity-violating magnetic order which we call the odd-parity magnetic multipole order. While this spontaneous order leavesPTsymmetry intact, the simultaneous violation ofPandTsymmetries gives rise to various emergent responses that are qualitatively different from those allowed by the nonmagneticP-symmetry breaking or by the ferromagnetic order. In this review, we introduce candidates hosting the intriguing spontaneous order and overview the characteristic physical responses. Various off-diagonal and/or nonreciprocal responses are identified, which are closely related to the unusual electronic structures such as hidden spin-momentum locking and asymmetric band dispersion.
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Affiliation(s)
- Hikaru Watanabe
- Research Center for Advanced Science and Technology, University of Tokyo, Meguro-ku, Tokyo 153-8904, Japan
| | - Youichi Yanase
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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2
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Lohmann M, Wickramaratne D, Moon J, Noyan M, Chuang HJ, Jonker BT, Li CH. Highly Efficient Spin-Orbit Torque Switching in Bi 2Se 3/Fe 3GeTe 2 van der Waals Heterostructures. ACS NANO 2024; 18:680-690. [PMID: 38109771 DOI: 10.1021/acsnano.3c09041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2023]
Abstract
Topological insulators (TIs) have shown promise as a spin-generating layer to switch the magnetization state of ferromagnets via spin-orbit torque (SOT) due to charge-to-spin conversion efficiency of the TI surface states that arises from spin-momentum locking. However, when TIs are interfaced with conventional bulk ferromagnetic metals, the combination of charge transfer and hybridization can potentially destroy the spin texture and hamper the possibility of accessing the TI surface states. Here, we fabricate an all van der Waals (vdW) heterostructure consisting of molecular beam epitaxy grown bulk-insulating Bi2Se3 and exfoliated 2D metallic ferromagnet Fe3GeTe2 (FGT) with perpendicular anisotropy. By detecting the magnetization state of the FGT via anomalous Hall effect and magneto-optical Kerr effect measurements, we determine the critical switching current density for magnetization switching to be Jc ≈ 1.2 × 106 A/cm2, the lowest reported for the switching of a perpendicular anisotropy ferromagnet using Bi2Se3. From second harmonic Hall measurements, we further determine the SOT efficiency (ξDL) to be in the range of 1.8 ± 0.3 and 1.4 ± 0.08 between 5 and 150 K, comparable to the highest values reported for Bi2Se3. Our density functional theory calculations find that the weak interlayer interactions at the Bi2Se3/FGT interface lead to a weakened dipole at the interface and suppress the proximity induced magnetic moment on Bi2Se3. This enables direct access to the TI surface states contributed by the first quintuple layer, where the spins are singly degenerate with significant net in-plane spin polarization. Our results highlight the clear advantage of all-vdW heterostructures with weak interlayer interactions that can enhance SOT efficiency and minimize critical current density, an important step toward realizing next generation low-power nonvolatile memory and spintronic devices.
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Affiliation(s)
- Mark Lohmann
- Materials Science and Technology Division, Naval Research Laboratory, Washington, D.C. 20375, United States
- American Society for Engineering Education, Washington, D.C. 20036, United States
| | - Darshana Wickramaratne
- Materials Science and Technology Division, Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Jisoo Moon
- Materials Science and Technology Division, Naval Research Laboratory, Washington, D.C. 20375, United States
- National Research Council, Washington, D.C. 20001, United States
| | - Mehmet Noyan
- Materials Science and Technology Division, Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Hsun-Jen Chuang
- Materials Science and Technology Division, Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Berend T Jonker
- Materials Science and Technology Division, Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Connie H Li
- Materials Science and Technology Division, Naval Research Laboratory, Washington, D.C. 20375, United States
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3
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Yuan W, Zhou LJ, Yang K, Zhao YF, Zhang R, Yan Z, Zhuo D, Mei R, Wang Y, Yi H, Chan MHW, Kayyalha M, Liu CX, Chang CZ. Electrical switching of the edge current chirality in quantum anomalous Hall insulators. NATURE MATERIALS 2024; 23:58-64. [PMID: 37857889 DOI: 10.1038/s41563-023-01694-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2023] [Accepted: 09/18/2023] [Indexed: 10/21/2023]
Abstract
A quantum anomalous Hall (QAH) insulator is a topological phase in which the interior is insulating but electrical current flows along the edges of the sample in either a clockwise or counterclockwise direction, as dictated by the spontaneous magnetization orientation. Such a chiral edge current eliminates any backscattering, giving rise to quantized Hall resistance and zero longitudinal resistance. Here we fabricate mesoscopic QAH sandwich Hall bar devices and succeed in switching the edge current chirality through thermally assisted spin-orbit torque (SOT). The well-quantized QAH states before and after SOT switching with opposite edge current chiralities are demonstrated through four- and three-terminal measurements. We show that the SOT responsible for magnetization switching can be generated by both surface and bulk carriers. Our results further our understanding of the interplay between magnetism and topological states and usher in an easy and instantaneous method to manipulate the QAH state.
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Affiliation(s)
- Wei Yuan
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Ling-Jie Zhou
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Kaijie Yang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Yi-Fan Zhao
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Ruoxi Zhang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Zijie Yan
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Deyi Zhuo
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Ruobing Mei
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Yang Wang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Hemian Yi
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Moses H W Chan
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Morteza Kayyalha
- Department of Electrical Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Chao-Xing Liu
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
| | - Cui-Zu Chang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
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4
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Jain R, Stanley M, Bose A, Richardella AR, Zhang XS, Pillsbury T, Muller DA, Samarth N, Ralph DC. Thermally generated spin current in the topological insulator Bi 2Se 3. SCIENCE ADVANCES 2023; 9:eadi4540. [PMID: 38091392 PMCID: PMC10848729 DOI: 10.1126/sciadv.adi4540] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Accepted: 11/14/2023] [Indexed: 02/12/2024]
Abstract
We present measurements of thermally generated transverse spin currents in the topological insulator Bi2Se3, thereby completing measurements of interconversions among the full triad of thermal gradients, charge currents, and spin currents. We accomplish this by comparing the spin Nernst magneto-thermopower to the spin Hall magnetoresistance for bilayers of Bi2Se3/CoFeB. We find that Bi2Se3 does generate substantial thermally driven spin currents. A lower bound for the ratio of spin current density to thermal gradient is [Formula: see text] = (4.9 ± 0.9) × 106 [Formula: see text], and a lower bound for the magnitude of the spin Nernst ratio is -0.61 ± 0.11. The spin Nernst ratio for Bi2Se3 is the largest among all materials measured to date, two to three times larger compared to previous measurements for the heavy metals Pt and W. Strong thermally generated spin currents in Bi2Se3 can be understood via Mott relations to be due to an overall large spin Hall conductivity and its dependence on electron energy.
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Affiliation(s)
- Rakshit Jain
- Department of Physics, Cornell University, Ithaca, NY 14853, USA
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
| | - Max Stanley
- Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA
| | - Arnab Bose
- Department of Physics, Cornell University, Ithaca, NY 14853, USA
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
| | - Anthony R. Richardella
- Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA
| | - Xiyue S. Zhang
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
| | - Timothy Pillsbury
- Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA
| | - David A. Muller
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
| | - Nitin Samarth
- Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA
| | - Daniel C. Ralph
- Department of Physics, Cornell University, Ithaca, NY 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
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5
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Binda F, Fedel S, Alvarado SF, Noël P, Gambardella P. Spin-Orbit Torques and Spin Hall Magnetoresistance Generated by Twin-Free and Amorphous Bi 0.9 Sb 0.1 Topological Insulator Films. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2304905. [PMID: 37568279 DOI: 10.1002/adma.202304905] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 07/28/2023] [Indexed: 08/13/2023]
Abstract
Topological insulators have attracted great interest as generators of spin-orbit torques (SOTs) in spintronic devices. Bi1-x Sbx is a prominent topological insulator that has a high charge-to-spin conversion efficiency. However, the origin and magnitude of the SOTs induced by current-injection in Bi1-x Sbx remain controversial. Here, the investigation of the SOTs and spin Hall magnetoresistance resulting from charge-to-spin conversion in twin-free epitaxial layers of Bi0.9 Sb0.1 (0001) coupled to FeCo are investigated, and compared with those of amorphous Bi0.9 Sb0.1 . A large charge-to-spin conversion efficiency of 1 in the first case and less than 0.1 in the second is found, confirming crystalline Bi0.9 Sb0.1 as a strong spin-injector material. The SOTs and spin Hall magnetoresistance are independent of the direction of the electric current, indicating that charge-to-spin conversion in single-crystal Bi0.9 Sb0.1 (0001) is isotropic despite the strong anisotropy of the topological surface states. Further, it is found that the damping-like SOT has a non-monotonic temperature dependence with a minimum at 20 K. By correlating the SOT with resistivity and weak antilocalization measurements, charge-spin conversion is concluded to occur via thermally excited holes from the bulk states above 20 K, and conduction through the isotropic surface states with increasing spin polarization due to decreasing electron-electron scattering below 20 K.
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Affiliation(s)
- Federico Binda
- Department of Materials, ETH Zurich, CH-8093, Zurich, Switzerland
| | - Stefano Fedel
- Department of Materials, ETH Zurich, CH-8093, Zurich, Switzerland
| | | | - Paul Noël
- Department of Materials, ETH Zurich, CH-8093, Zurich, Switzerland
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6
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Jiang M, Asahara H, Ohya S, Tanaka M. Electric Field Control of Spin-Orbit Torque Magnetization Switching in a Spin-Orbit Ferromagnet Single Layer. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023; 10:e2301540. [PMID: 37329321 PMCID: PMC10460875 DOI: 10.1002/advs.202301540] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2023] [Revised: 04/29/2023] [Indexed: 06/19/2023]
Abstract
To achieve a desirable magnitude of spin-orbit torque (SOT) for magnetization switching and realize multifunctional spin logic and memory devices utilizing SOT, controlling the SOT manipulation is vitally important. In conventional SOT bilayer systems, researchers have tried to control the magnetization switching behavior via interfacial oxidization, modulation of spin-orbit effective field, and effective spin Hall angle; however, the switching efficiency is limited by the interface quality. A current-induced effective magnetic field in a single layer of a ferromagnet with strong spin-orbit interactions, the so-called spin-orbit ferromagnet, can be utilized to induce SOT. In spin-orbit ferromagnet systems, electric field application has the potential for manipulating the spin-orbit interactions via carrier concentration modulation. In this work, it is demonstrated that SOT magnetization switching can be successfully controlled via an external electric field using a (Ga, Mn)As single layer. By applying a gate voltage, the switching current density can be solidly and reversibly manipulated with a large ratio of 14.5%, which is ascribed to the successful modulation of the interfacial electric field. The findings of this work help further the understanding of the magnetization switching mechanism and advance the development of gate-controlled SOT devices.
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Affiliation(s)
- Miao Jiang
- School of Materials Science and EngineeringBeijing Institute of TechnologyZhongguancun South Street No.5, HaidianBeijing100081China
- Department of Electrical Engineering and Information SystemsThe University of Tokyo7‐3‐1 Hongo, Bunkyo‐kuTokyo113‐8656Japan
| | - Hirokatsu Asahara
- Department of Electrical Engineering and Information SystemsThe University of Tokyo7‐3‐1 Hongo, Bunkyo‐kuTokyo113‐8656Japan
| | - Shinobu Ohya
- Department of Electrical Engineering and Information SystemsThe University of Tokyo7‐3‐1 Hongo, Bunkyo‐kuTokyo113‐8656Japan
- Center for Spintronics Research Network (CSRN)Graduate School of EngineeringThe University of Tokyo7‐3‐1 Hongo, Bunkyo‐kuTokyo113‐8656Japan
| | - Masaaki Tanaka
- Department of Electrical Engineering and Information SystemsThe University of Tokyo7‐3‐1 Hongo, Bunkyo‐kuTokyo113‐8656Japan
- Center for Spintronics Research Network (CSRN)Graduate School of EngineeringThe University of Tokyo7‐3‐1 Hongo, Bunkyo‐kuTokyo113‐8656Japan
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7
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Yokouchi T, Ikeda Y, Morimoto T, Shiomi Y. Giant Magnetochiral Anisotropy in Weyl Semimetal WTe_{2} Induced by Diverging Berry Curvature. PHYSICAL REVIEW LETTERS 2023; 130:136301. [PMID: 37067327 DOI: 10.1103/physrevlett.130.136301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Accepted: 03/08/2023] [Indexed: 06/19/2023]
Abstract
The concept of Berry curvature is essential for various transport phenomena. However, an effect of the Berry curvature on magnetochiral anisotropy, i.e., nonreciprocal magnetotransport, is still elusive. Here, we report that the Berry curvature induces the large magnetochiral anisotropy. In Weyl semimetal WTe_{2}, we observe the strong enhancement of the magnetochiral anisotropy when the Fermi level is located near the Weyl points. Notably, the maximal figure of merit γ[over ¯] reaches 1.2×10^{-6} m^{2} T^{-1} A^{-1}, which is the largest ever reported in bulk materials. Our semiclassical calculation shows that the diverging Berry curvature at the Weyl points strongly enhances the magnetochiral anisotropy.
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Affiliation(s)
- Tomoyuki Yokouchi
- Department of Basic Science, The University of Tokyo, Tokyo 152-8902, Japan
| | - Yuya Ikeda
- Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
| | - Takahiro Morimoto
- Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
| | - Yuki Shiomi
- Department of Basic Science, The University of Tokyo, Tokyo 152-8902, Japan
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8
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Zhang Y, Kalappattil V, Liu C, Mehraeen M, Zhang SSL, Ding J, Erugu U, Chen Z, Tian J, Liu K, Tang J, Wu M. Large magnetoelectric resistance in the topological Dirac semimetal α-Sn. SCIENCE ADVANCES 2022; 8:eabo0052. [PMID: 35905193 PMCID: PMC9337753 DOI: 10.1126/sciadv.abo0052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Accepted: 06/14/2022] [Indexed: 06/15/2023]
Abstract
The spin-momentum locking of surface states in topological materials can produce a resistance that scales linearly with magnetic and electric fields. Such a bilinear magnetoelectric resistance (BMER) effect offers a new approach for information reading and field sensing applications, but the effects demonstrated so far are too weak or for low temperatures. This article reports the first observation of BMER effects in topological Dirac semimetals; the BMER responses were measured at room temperature and were substantially stronger than those reported previously. The experiments used topological Dirac semimetal α-Sn thin films grown on silicon substrates. The films showed BMER responses that are 106 times larger than previously measured at room temperature and are also larger than those previously obtained at low temperatures. These results represent a major advance toward realistic BMER applications. Significantly, the data also yield the first characterization of three-dimensional Fermi-level spin texture of topological surface states in α-Sn.
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Affiliation(s)
- Yuejie Zhang
- Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
- School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | | | - Chuanpu Liu
- Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
| | - M. Mehraeen
- Department of Physics, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Steven S.-L. Zhang
- Department of Physics, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Jinjun Ding
- Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
| | - Uppalaiah Erugu
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
| | - Zhijie Chen
- Physics Department, Georgetown University, Washington, DC 20057, USA
| | - Jifa Tian
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
| | - Kai Liu
- Physics Department, Georgetown University, Washington, DC 20057, USA
| | - Jinke Tang
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
| | - Mingzhong Wu
- Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
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9
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Zhao YF, Zhang R, Zhou LJ, Mei R, Yan ZJ, Chan MHW, Liu CX, Chang CZ. Zero Magnetic Field Plateau Phase Transition in Higher Chern Number Quantum Anomalous Hall Insulators. PHYSICAL REVIEW LETTERS 2022; 128:216801. [PMID: 35687436 DOI: 10.1103/physrevlett.128.216801] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Accepted: 05/06/2022] [Indexed: 06/15/2023]
Abstract
The plateau-to-plateau transition in quantum Hall effect under high magnetic fields is a celebrated quantum phase transition between two topological states. It can be achieved by either sweeping the magnetic field or tuning the carrier density. The recent realization of the quantum anomalous Hall (QAH) insulators with tunable Chern numbers introduces the channel degree of freedom to the dissipation-free chiral edge transport and makes the study of the quantum phase transition between two topological states under zero magnetic field possible. Here, we synthesized the magnetic topological insulator (TI)/TI pentalayer heterostructures with different Cr doping concentrations in the middle magnetic TI layers using molecular beam epitaxy. By performing transport measurements, we found a potential plateau phase transition between C=1 and C=2 QAH states under zero magnetic field. In tuning the transition, the Hall resistance monotonically decreases from h/e^{2} to h/2e^{2}, concurrently, the longitudinal resistance exhibits a maximum at the critical point. Our results show that the ratio between the Hall resistance and the longitudinal resistance is greater than 1 at the critical point, which indicates that the original chiral edge channel from the C=1 QAH state coexists with the dissipative bulk conduction channels. Subsequently, these bulk conduction channels appear to self-organize and form the second chiral edge channel in completing the plateau phase transition. Our study will motivate further investigations of this novel Chern number change-induced quantum phase transition and advance the development of the QAH chiral edge current-based electronic and spintronic devices.
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Affiliation(s)
- Yi-Fan Zhao
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Ruoxi Zhang
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Ling-Jie Zhou
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Ruobing Mei
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Zi-Jie Yan
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Moses H W Chan
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Chao-Xing Liu
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Cui-Zu Chang
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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10
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Fan T, Khang NHD, Nakano S, Hai PN. Ultrahigh efficient spin orbit torque magnetization switching in fully sputtered topological insulator and ferromagnet multilayers. Sci Rep 2022; 12:2998. [PMID: 35194059 PMCID: PMC8863830 DOI: 10.1038/s41598-022-06779-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2021] [Accepted: 02/07/2022] [Indexed: 11/09/2022] Open
Abstract
Spin orbit torque (SOT) magnetization switching of ferromagnets with large perpendicular magnetic anisotropy has a great potential for the next generation non-volatile magnetoresistive random-access memory (MRAM). It requires a high performance pure spin current source with a large spin Hall angle and high electrical conductivity, which can be fabricated by a mass production technique. In this work, we demonstrate ultrahigh efficient and robust SOT magnetization switching in fully sputtered BiSb topological insulator and perpendicularly magnetized Co/Pt multilayers. Despite fabricated by the magnetron sputtering instead of the laboratory molecular beam epitaxy, the topological insulator layer, BiSb, shows a large spin Hall angle of θSH = 10.7 and high electrical conductivity of σ = 1.5 × 105 Ω-1 m-1. Our results demonstrate the feasibility of BiSb topological insulator for implementation of ultralow power SOT-MRAM and other SOT-based spintronic devices.
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Affiliation(s)
- Tuo Fan
- Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8550, Japan
| | - Nguyen Huynh Duy Khang
- Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8550, Japan
- Department of Physics, Ho Chi Minh City University of Education, 280 An Duong Vuong Street, District 5, Ho Chi Minh City, 738242, Vietnam
| | - Soichiro Nakano
- Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8550, Japan
| | - Pham Nam Hai
- Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8550, Japan.
- Center for Spintronics Research Network (CSRN), The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-8656, Japan.
- CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.
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11
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Ngabonziza P. Quantum transport and potential of topological states for thermoelectricity in Bi 2Te 3thin films. NANOTECHNOLOGY 2022; 33:192001. [PMID: 35081521 DOI: 10.1088/1361-6528/ac4f17] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 01/26/2022] [Indexed: 06/14/2023]
Abstract
This paper reviews recent developments in quantum transport and it presents current efforts to explore the contribution of topological insulator boundary states to thermoelectricity in Bi2Te3thin films. Although Bi2Te3has been used as a thermoelectric material for many years, it is only recently that thin films of this material have been synthesized as 3D topological insulators with interesting physics and potential applications related to topologically protected surface states. A major bottleneck in Bi2Te3thin films has been eliminating its bulk conductivity while increasing its crystal quality. The ability to grow epitaxial films with high crystal quality and to fabricate sophisticated Bi2Te3-based devices is attractive for implementing a variety of topological quantum devices and exploring the potential of topological states to improve thermoelectric properties. Special emphasis is laid on preparing low-defect-density Bi2Te3epitaxial films, gate-tuning of normal-state transport and Josephson supercurrent in topological insulator/superconductor hybrid devices. Prospective quantum transport experiments on Bi2Te3thin-film devices are discussed as well. Finally, an overview of current progress on the contribution of topological insulator boundary states to thermoelectricity is presented. Future explorations to reveal the potential of topological states for improving thermoelectric properties of Bi2Te3films and realizing high-performance thermoelectric devices are discussed.
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Affiliation(s)
- Prosper Ngabonziza
- Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany
- Department of Physics, University of Johannesburg, PO Box 524, Auckland Park 2006, Johannesburg, South Africa
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12
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Ye C, Xie X, Lv W, Huang K, Yang AJ, Jiang S, Liu X, Zhu D, Qiu X, Tong M, Zhou T, Hsu CH, Chang G, Lin H, Li P, Yang K, Wang Z, Jiang T, Renshaw Wang X. Nonreciprocal Transport in a Bilayer of MnBi 2Te 4 and Pt. NANO LETTERS 2022; 22:1366-1373. [PMID: 35073094 DOI: 10.1021/acs.nanolett.1c04756] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
MnBi2Te4 (MBT) is the first intrinsic magnetic topological insulator with the interaction of spin-momentum locked surface electrons and intrinsic magnetism, and it exhibits novel magnetic and topological phenomena. Recent studies suggested that the interaction of electrons and magnetism can be affected by the Mn-doped Bi2Te3 phase at the surface due to inevitable structural defects. Here, we report an observation of nonreciprocal transport, that is, current-direction-dependent resistance, in a bilayer composed of antiferromagnetic MBT and nonmagnetic Pt. The emergence of the nonreciprocal response below the Néel temperature confirms a correlation between nonreciprocity and intrinsic magnetism in the surface state of MBT. The angular dependence of the nonreciprocal transport indicates that nonreciprocal response originates from the asymmetry scattering of electrons at the surface of MBT mediated by magnon. Our work provides an insight into nonreciprocity arising from the correlation between magnetism and Dirac surface electrons in intrinsic magnetic topological insulators.
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Affiliation(s)
- Chen Ye
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link 637371, Singapore
| | - Xiangnan Xie
- State Key Laboratory of High Performance Computing, College of Computer Science and Technology, National University of Defense Technology, Changsha 410073, P.R. China
| | - Wenxing Lv
- Physics Laboratory, Industrial Training Center, Shenzhen Polytechnic, Shenzhen, Guangdong 518055, P.R. China
| | - Ke Huang
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link 637371, Singapore
| | - Allen Jian Yang
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link 637371, Singapore
| | - Sicong Jiang
- Department of NanoEngineering and Program of Chemical Engineering, University of California San Diego, La Jolla, California 92093-0448, United States
- Program of Materials Science and Engineering, University of California San Diego, La Jolla, California 92093-0418, United States
| | - Xue Liu
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link 637371, Singapore
- Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, P.R. China
| | - Dapeng Zhu
- Fert Beijing Institute, MIIT Key Laboratory of Spintronics, School of Integrated Circuit Science and Engineering, Beihang University, Beijing 100191, P.R. China
- Beihang-Goertek Joint Microelectronics Institute, Qingdao Research Institute, Beihang University, Qingdao 266000, P.R. China
| | - Xuepeng Qiu
- Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology and School of Physics Science and Engineering, Tongji University, Shanghai 200092, P.R. China
| | - Mingyu Tong
- College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, P.R. China
| | - Tong Zhou
- State Key Laboratory of High Performance Computing, College of Computer Science and Technology, National University of Defense Technology, Changsha 410073, P.R. China
| | - Chuang-Han Hsu
- Insitute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Guoqing Chang
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link 637371, Singapore
| | - Hsin Lin
- Insitute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Peisen Li
- College of Intelligence Science and Technology, National University of Defense Technology, Changsha 410073, P.R. China
| | - Kesong Yang
- Department of NanoEngineering and Program of Chemical Engineering, University of California San Diego, La Jolla, California 92093-0448, United States
- Program of Materials Science and Engineering, University of California San Diego, La Jolla, California 92093-0418, United States
| | - Zhenyu Wang
- State Key Laboratory of High Performance Computing, College of Computer Science and Technology, National University of Defense Technology, Changsha 410073, P.R. China
- National Innovation Institute of Defense Technology, Academy of Military Sciences PLA China, Beijing 100010, P.R. China
- Beijing Academy of Quantum Information Sciences, Beijing 100084, P.R. China
| | - Tian Jiang
- State Key Laboratory of High Performance Computing, College of Computer Science and Technology, National University of Defense Technology, Changsha 410073, P.R. China
- Beijing Institute for Advanced Study, National University of Defense Technology, Changsha 410073, P.R. China
| | - Xiao Renshaw Wang
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link 637371, Singapore
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore
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13
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Freimuth F, Blügel S, Mokrousov Y. Theory of unidirectional magnetoresistance and nonlinear Hall effect. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 34:055301. [PMID: 34678787 DOI: 10.1088/1361-648x/ac327f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Accepted: 10/22/2021] [Indexed: 06/13/2023]
Abstract
We study the unidirectional magnetoresistance (UMR) and the nonlinear Hall effect (NLHE) in the ferromagnetic Rashba model. For this purpose we derive expressions to describe the response of the electric current quadratic in the applied electric field. We compare two different formalisms, namely the standard Keldysh nonequilibrium formalism and the Moyal-Keldysh formalism, to derive the nonlinear conductivities of UMR and NLHE. We find that both formalisms lead to identical numerical results when applied to the ferromagnetic Rashba model. The UMR and the NLHE nonlinear conductivities tend to be comparable in magnitude according to our calculations. Additionally, their dependencies on the Rashba parameter and on the quasiparticle broadening are similar. The nonlinear zero-frequency response considered here is several orders of magnitude higher than the one at optical frequencies that describes the photocurrent generation in the ferromagnetic Rashba model. Additionally, we compare our Keldysh nonequilibrium expression in the independent-particle approximation to literature expressions of the UMR that have been obtained within the constant relaxation time approximation of the Boltzmann formalism. We find that both formalisms converge to the same analytical formula in the limit of infinite relaxation time. However, remarkably, we find that the Boltzmann result does not correspond to the intraband term of the Keldysh expression. Instead, the Boltzmann result corresponds to the sum of the intraband term and an interband term that can be brought into the form of an effective intraband term due to thef-sum rule.
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Affiliation(s)
- Frank Freimuth
- 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
| | - Stefan Blügel
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - 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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14
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Abstract
Giant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 105 A cm−2 have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiency θSH in TIs is quantified by both the SOT-induced shift of the magnetic switching field (θSH = 1.59) and the SOT-induced ferromagnetic resonance (ST-FMR) (θSH = 1.02), which is one order of magnitude larger than that in conventional heavy metals. These results inspire a revolution of SOT-MRAM from classical to quantum materials, with great potential to further reduce the energy consumption. It remains challenging to integrate topological insulators (TI) with magnetic tunnel junctions (MTJ) for spintronics applications. Here, the authors achieve a large tunneling magnetoresistance ratio and a low switching current density in a TI-MTJ device at room temperature, very promising for TI-driven magnetic memory.
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15
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Tang W, Liu H, Li Z, Pan A, Zeng Y. Spin-Orbit Torque in Van der Waals-Layered Materials and Heterostructures. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2021; 8:e2100847. [PMID: 34323390 PMCID: PMC8456225 DOI: 10.1002/advs.202100847] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Revised: 06/03/2021] [Indexed: 06/13/2023]
Abstract
Spin-orbit torque (SOT) opens an efficient and versatile avenue for the electrical manipulation of magnetization in spintronic devices. The enhancement of SOT efficiency and reduction of power consumption are key points for the implementation of high-performance SOT devices, which strongly rely on the spin-orbit coupling (SOC) strength and magnetic properties of ferromagnetic/non-magnetic heterostructures. Recently, van der Waals-layered materials have shown appealing properties for use in efficient SOT applications. On the one hand, transition-metal dichalcogenides, topological insulators, and graphene-based heterostructures possess appreciable SOC strength. This feature can efficiently converse the charge current into spin current and result in large SOT. On the other hand, the newly discovered layered magnetic materials provide ultra-thin and gate-tunable ferromagnetic candidates for high-performance SOT devices. In this review, the latest advancements of SOT research in various layered materials are summarized. First, a brief introduction of SOT is given. Second, SOT studies of various layered materials and heterostructures are summarized. Subsequently, progresses on SOT-induced magnetization switching are presented. Finally, current challenges and prospects for future development are suggested.
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Affiliation(s)
- Wei Tang
- Key laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong ProvinceCollege of Physics and Optoelectronic EngineeringShenzhen UniversityShenzhen518060China
| | - Haoliang Liu
- State Key Laboratory on Tunable Laser TechnologyMinistry of Industry and Information Technology Key Lab of Micro‐Nano Optoelectronic Information SystemSchool of ScienceHarbin Institute of TechnologyShenzhen518055China
| | - Zhe Li
- State Key Laboratory on Tunable Laser TechnologyMinistry of Industry and Information Technology Key Lab of Micro‐Nano Optoelectronic Information SystemSchool of ScienceHarbin Institute of TechnologyShenzhen518055China
| | - Anlian Pan
- Key Laboratory for Micro‐Nano Physics and Technology of Hunan ProvinceCollege of Materials Science and EngineeringHunan UniversityChangsha410082China
| | - Yu‐Jia Zeng
- Key laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong ProvinceCollege of Physics and Optoelectronic EngineeringShenzhen UniversityShenzhen518060China
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16
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Ding J, Liu C, Kalappattil V, Zhang Y, Mosendz O, Erugu U, Yu R, Tian J, DeMann A, Field SB, Yang X, Ding H, Tang J, Terris B, Fert A, Chen H, Wu M. Switching of a Magnet by Spin-Orbit Torque from a Topological Dirac Semimetal. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2005909. [PMID: 33938060 DOI: 10.1002/adma.202005909] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Indexed: 06/12/2023]
Abstract
Recent experiments show that topological surface states (TSS) in topological insulators (TI) can be exploited to manipulate magnetic ordering in ferromagnets. In principle, TSS should also exist for other topological materials, but it remains unexplored as to whether such states can also be utilized to manipulate ferromagnets. Herein, current-induced magnetization switching enabled by TSS in a non-TI topological material, namely, a topological Dirac semimetal α-Sn, is reported. The experiments use an α-Sn/Ag/CoFeB trilayer structure. The magnetization in the CoFeB layer can be switched by a charge current at room temperature, without an external magnetic field. The data show that the switching is driven by the TSS of the α-Sn layer, rather than spin-orbit coupling in the bulk of the α-Sn layer or current-produced heating. The switching efficiency is as high as in TI systems. This shows that the topological Dirac semimetal α-Sn is as promising as TI materials in terms of spintronic applications.
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Affiliation(s)
- Jinjun Ding
- Department of Physics, Colorado State University, Fort Collins, CO, 80523, USA
| | - Chuanpu Liu
- Department of Physics, Colorado State University, Fort Collins, CO, 80523, USA
| | | | - Yuejie Zhang
- Department of Physics, Colorado State University, Fort Collins, CO, 80523, USA
- School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Oleksandr Mosendz
- Western Digital Research Center, Western Digital Corporation, San Jose, CA, 95119, USA
| | - Uppalaiah Erugu
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY, 82071, USA
| | - Rui Yu
- Department of Physics, Colorado State University, Fort Collins, CO, 80523, USA
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing, Jiangsu, 210093, China
| | - Jifa Tian
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY, 82071, USA
| | - August DeMann
- Department of Physics, Colorado State University, Fort Collins, CO, 80523, USA
| | - Stuart B Field
- Department of Physics, Colorado State University, Fort Collins, CO, 80523, USA
| | - Xiaofei Yang
- School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Haifeng Ding
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing, Jiangsu, 210093, China
| | - Jinke Tang
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY, 82071, USA
| | - Bruce Terris
- Western Digital Research Center, Western Digital Corporation, San Jose, CA, 95119, USA
| | - Albert Fert
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, Palaiseau, 91767, France
| | - Hua Chen
- Department of Physics, Colorado State University, Fort Collins, CO, 80523, USA
- School of Advanced Materials Discovery, Colorado State University, Fort Collins, CO, 80523, USA
| | - Mingzhong Wu
- Department of Physics, Colorado State University, Fort Collins, CO, 80523, USA
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17
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Current-induced switching of proximity-induced ferromagnetic surface states in a topological insulator. Nat Commun 2021; 12:1404. [PMID: 33658496 PMCID: PMC7930265 DOI: 10.1038/s41467-021-21672-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Accepted: 02/07/2021] [Indexed: 11/08/2022] Open
Abstract
Electrical manipulation of magnetization could be an essential function for energy-efficient spintronics technology. A magnetic topological insulator, possessing a magnetically gapped surface state with spin-polarized electrons, not only exhibits exotic topological phases relevant to the quantum anomalous Hall state but also enables the electrical control of its magnetic state at the surface. Here, we demonstrate efficient current-induced switching of the surface ferromagnetism in hetero-bilayers consisting of the topological insulator (Bi1-xSbx)2Te3 and the ferromagnetic insulator Cr2Ge2Te6, where the proximity-induced ferromagnetic surface states play two roles: efficient charge-to-spin current conversion and emergence of large anomalous Hall effect. The sign reversal of the surface ferromagnetic states with current injection is clearly observed, accompanying the nearly full magnetization reversal in the adjacent insulating Cr2Ge2Te6 layer of an optimal thickness range. The present results may facilitate an electrical control of dissipationless topological-current circuits. Electrical manipulation of magnetization in devices made of topological materials may be an essential route towards future spintronics technology. Here, Mogi et al. show efficient current-induced switching of surface ferromagnetism in hetero-bilayers of topological insulator (Bi1-xSbx)2Te3 and ferromagnetic insulator Cr2Ge2Te6.
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18
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Shao Q, Li P, Liu L, Yang H, Fukami S, Razavi A, Wu H, Wang K, Freimuth F, Mokrousov Y, Stiles MD, Emori S, Hoffmann A, Åkerman J, Roy K, Wang JP, Yang SH, Garello K, Zhang W. Roadmap of spin-orbit torques. IEEE TRANSACTIONS ON MAGNETICS 2021; 57:10.48550/arXiv.2104.11459. [PMID: 37057056 PMCID: PMC10091395 DOI: 10.48550/arxiv.2104.11459] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Spin-orbit torque (SOT) is an emerging technology that enables the efficient manipulation of spintronic devices. The initial processes of interest in SOTs involved electric fields, spin-orbit coupling, conduction electron spins and magnetization. More recently interest has grown to include a variety of other processes that include phonons, magnons, or heat. Over the past decade, many materials have been explored to achieve a larger SOT efficiency. Recently, holistic design to maximize the performance of SOT devices has extended material research from a nonmagnetic layer to a magnetic layer. The rapid development of SOT has spurred a variety of SOT-based applications. In this Roadmap paper, we first review the theories of SOTs by introducing the various mechanisms thought to generate or control SOTs, such as the spin Hall effect, the Rashba-Edelstein effect, the orbital Hall effect, thermal gradients, magnons, and strain effects. Then, we discuss the materials that enable these effects, including metals, metallic alloys, topological insulators, two-dimensional materials, and complex oxides. We also discuss the important roles in SOT devices of different types of magnetic layers, such as magnetic insulators, antiferromagnets, and ferrimagnets. Afterward, we discuss device applications utilizing SOTs. We discuss and compare three-terminal and two-terminal SOT-magnetoresistive random-access memories (MRAMs); we mention various schemes to eliminate the need for an external field. We provide technological application considerations for SOT-MRAM and give perspectives on SOT-based neuromorphic devices and circuits. In addition to SOT-MRAM, we present SOT-based spintronic terahertz generators, nano-oscillators, and domain wall and skyrmion racetrack memories. This paper aims to achieve a comprehensive review of SOT theory, materials, and applications, guiding future SOT development in both the academic and industrial sectors.
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Affiliation(s)
- Qiming Shao
- Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology
| | - Peng Li
- Department of Electrical and Computer Engineering, Auburn University
| | - Luqiao Liu
- Electrical Engineering and Computer Science, Massachusetts Institute of Technology
| | - Hyunsoo Yang
- Department of Electrical and Computer Engineering, National University of Singapore
| | - Shunsuke Fukami
- Research Institute of Electrical Communication, Tohoku University
| | - Armin Razavi
- Department of Electrical and Computer Engineering, University of California, Los Angeles
| | - Hao Wu
- Department of Electrical and Computer Engineering, University of California, Los Angeles
| | - Kang Wang
- Department of Electrical and Computer Engineering, University of California, Los Angeles
| | | | | | - Mark D Stiles
- Alternative Computing Group, National Institute of Standards and Technology
| | | | - Axel Hoffmann
- Department of Materials Science and Engineering, University of Illinois Urbana-Champaign
| | | | - Kaushik Roy
- Department of Electrical and Computer Engineering, Purdue University
| | - Jian-Ping Wang
- Electrical and Computer Engineering Department, University of Minnesota
| | | | - Kevin Garello
- IMEC, Leuven, Belgium; CEA-Spintec, Grenoble, France
| | - Wei Zhang
- Physics Department, Oakland University
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19
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Ryu J, Lee S, Lee KJ, Park BG. Current-Induced Spin-Orbit Torques for Spintronic Applications. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e1907148. [PMID: 32141681 DOI: 10.1002/adma.201907148] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 12/13/2019] [Indexed: 06/10/2023]
Abstract
Control of magnetization in magnetic nanostructures is essential for development of spintronic devices because it governs fundamental device characteristics such as energy consumption, areal density, and operation speed. In this respect, spin-orbit torque (SOT), which originates from the spin-orbit interaction, has been widely investigated due to its efficient manipulation of the magnetization using in-plane current. SOT spearheads novel spintronic applications including high-speed magnetic memories, reconfigurable logics, and neuromorphic computing. Herein, recent advances in SOT research, highlighting the considerable benefits and challenges of SOT-based spintronic devices, are reviewed. First, the materials and structural engineering that enhances SOT efficiency are discussed. Then major experimental results for field-free SOT switching of perpendicular magnetization are summarized, which includes the introduction of an internal effective magnetic field and the generation of a distinct spin current with out-of-plane spin polarization. Finally, advanced SOT functionalities are presented, focusing on the demonstration of reconfigurable and complementary operation in spin logic devices.
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Affiliation(s)
- Jeongchun Ryu
- Department of Materials Science and Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Soogil Lee
- Department of Materials Science and Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Kyung-Jin Lee
- Department of Materials Science and Engineering and KU-KIST Graduate School of Converging Science and Technology, Korea University, 145 Anam-ro, Anam-dong, Seongbuk-gu, Seoul, 02841, Republic of Korea
| | - Byong-Guk Park
- Department of Materials Science and Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
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20
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Fei F, Zhang S, Zhang M, Shah SA, Song F, Wang X, Wang B. The Material Efforts for Quantized Hall Devices Based on Topological Insulators. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e1904593. [PMID: 31840308 DOI: 10.1002/adma.201904593] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Revised: 09/09/2019] [Indexed: 06/10/2023]
Abstract
A topological insulator (TI) is a kind of novel material hosting a topological band structure and plenty of exotic topological quantum effects. Achieving quantized electrical transport, including the quantum Hall effect (QHE) and the quantum anomalous Hall effect (QAHE), is an important aspect of realizing quantum devices based on TI materials. Intense efforts are made in this field, in which the most essential research is based on the optimization of realistic TI materials. Herein, the TI material development process is reviewed, focusing on the realization of quantized transport. Especially, for QHE, the strategies to increase the surface transport ratio and decrease the threshold magnetic field of QHE are examined. For QAHE, the evolution history of magnetic TIs is introduced, and the recently discovered magnetic TI candidates with intrinsic magnetizations are discussed in detail. Moreover, future research perspectives on these novel topological quantum effects are also evaluated.
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Affiliation(s)
- Fucong Fei
- National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Shuai Zhang
- National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Minhao Zhang
- National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Syed Adil Shah
- National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Fengqi Song
- National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Xuefeng Wang
- National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China
| | - Baigeng Wang
- National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
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21
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Che X, Pan Q, Vareskic B, Zou J, Pan L, Zhang P, Yin G, Wu H, Shao Q, Deng P, Wang KL. Strongly Surface State Carrier-Dependent Spin-Orbit Torque in Magnetic Topological Insulators. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e1907661. [PMID: 32108391 DOI: 10.1002/adma.201907661] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Revised: 01/28/2020] [Indexed: 06/10/2023]
Abstract
The topological surface states (TSS) in topological insulators (TIs) can exert strong spin-orbit torque (SOT) on adjacent magnetization, offering great potential in implementing energy-efficient magnetic memory devices. However, there are large discrepancies among the reported spin Hall angle values in TIs, and its temperature dependence still remains elusive. Here, the spin Hall angle in a modulation-doped Cr-Bix Sb2- x Te3 (Cr-BST) film is quantitatively determined via both transport and optic approaches, where consistent results are obtained. A large spin Hall angle of ≈90 in the modulation-doped Cr-BST film is demonstrated at 2.5 K, and the spin Hall angle drastically decreases to 0.3-0.5 as the temperature increases. Moreover, by tuning the top TSS carrier concentration, a competition between the top and bottom TSS in contributing to SOT is observed. The above phenomena can account for the large discrepancies among the previously reported spin Hall angle values and reveal the unique role of TSS in generating SOT.
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Affiliation(s)
- Xiaoyu Che
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Quanjun Pan
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Božo Vareskic
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Jingyi Zou
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Lei Pan
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Peng Zhang
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Gen Yin
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Hao Wu
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Qiming Shao
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
- Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 999077, China
| | - Peng Deng
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
| | - Kang L Wang
- Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA
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Chi Z, Lau YC, Xu X, Ohkubo T, Hono K, Hayashi M. The spin Hall effect of Bi-Sb alloys driven by thermally excited Dirac-like electrons. SCIENCE ADVANCES 2020; 6:eaay2324. [PMID: 32181344 PMCID: PMC7060068 DOI: 10.1126/sciadv.aay2324] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 11/27/2019] [Indexed: 05/26/2023]
Abstract
We have studied the charge to spin conversion in Bi1-x Sb x /CoFeB heterostructures. The spin Hall conductivity (SHC) of the sputter-deposited heterostructures exhibits a high plateau at Bi-rich compositions, corresponding to the topological insulator phase, followed by a decrease of SHC for Sb-richer alloys, in agreement with the calculated intrinsic spin Hall effect of Bi1-x Sb x . The SHC increases with increasing Bi1-x Sb x thickness before it saturates, indicating that it is the bulk of the alloy that predominantly contributes to the generation of spin current; the topological surface states, if present, play little role. Unexpectedly, the SHC is found to increase with increasing temperature, following the trend of carrier density. These results suggest that the large SHC at room temperature, with a spin Hall efficiency exceeding 1 and an extremely large spin current mobility, is due to increased number of thermally excited Dirac-like electrons in the L valley of the narrow gap Bi1-x Sb x alloy.
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Affiliation(s)
- Zhendong Chi
- Department of Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
| | - Yong-Chang Lau
- Department of Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
- Institute for Materials Research (IMR), Tohoku University, Sendai 980-8577, Japan
| | - Xiandong Xu
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
| | - Tadakatsu Ohkubo
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
| | - Kazuhiro Hono
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
| | - Masamitsu Hayashi
- Department of Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
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Bhalla P, MacDonald AH, Culcer D. Resonant Photovoltaic Effect in Doped Magnetic Semiconductors. PHYSICAL REVIEW LETTERS 2020; 124:087402. [PMID: 32167346 DOI: 10.1103/physrevlett.124.087402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Accepted: 02/05/2020] [Indexed: 06/10/2023]
Abstract
The rectified nonlinear response of a clean, time-reversal symmetric, undoped semiconductor to an ac electric field includes a well known intrinsic shift current. We show that when Kramers degeneracy is broken, a distinct second order rectified response appears due to Bloch state anomalous velocities in a system with an oscillating Fermi surface. This effect, which we refer to as the resonant photovoltaic effect, produces a resonant galvanic current peak at the interband absorption threshold in doped semiconductors or semimetals with approximate particle-hole symmetry. We evaluate the resonant photovoltaic effect for a model of the surface states of a magnetized topological insulator.
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Affiliation(s)
- Pankaj Bhalla
- Beijing Computational Science Research Center, Beijing 100193, China
- School of Physics, University of New South Wales, Sydney 2052, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, University of New South Wales Node, Sydney 2052, Australia
| | - Allan H MacDonald
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Dimitrie Culcer
- School of Physics, University of New South Wales, Sydney 2052, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, University of New South Wales Node, Sydney 2052, Australia
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24
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Wu H, Zhang P, Deng P, Lan Q, Pan Q, Razavi SA, Che X, Huang L, Dai B, Wong K, Han X, Wang KL. Room-Temperature Spin-Orbit Torque from Topological Surface States. PHYSICAL REVIEW LETTERS 2019; 123:207205. [PMID: 31809108 DOI: 10.1103/physrevlett.123.207205] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2019] [Indexed: 06/10/2023]
Abstract
Spin-momentum locked surface states in topological insulators (TIs) provide a promising route for achieving high spin-orbit torque (SOT) efficiency beyond the bulk spin-orbit coupling in heavy metals (HMs). However, in previous works, there is a huge discrepancy among the quantitative SOTs from TIs in various systems determined by different methods. Here, we systematically study the SOT in the TI(HM)/Ti/CoFeB/MgO systems by the same method, and make a conclusive assessment of SOT efficiency for TIs and HMs. Our results demonstrate that TIs show more than one order of magnitude higher SOT efficiency than HMs even at room temperature, at the same time the switching current density as low as 5.2×10^{5} A cm^{-2} is achieved with (Bi_{1-x}Sb_{x})_{2}Te_{3}. Furthermore, we investigate the relationship between SOT efficiency and the position of Fermi level in (Bi_{1-x}Sb_{x})_{2}Te_{3}, where the SOT efficiency is significantly enhanced near the Dirac point, with the most insulating bulk and conducting surface states, indicating the dominating SOT contribution from topological surface states. This work unambiguously demonstrates the ultrahigh SOT efficiency from topological surface states.
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Affiliation(s)
- Hao Wu
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Peng Zhang
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Peng Deng
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Qianqian Lan
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, Jülich 52425, Germany
| | - Quanjun Pan
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Seyed Armin Razavi
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Xiaoyu Che
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Li Huang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Bingqian Dai
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Kin Wong
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Xiufeng Han
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Kang L Wang
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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25
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Arabikhah M, Saffarzadeh A. Surface state transport in double-gated and magnetized topological insulators with hexagonal warping effects. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:445001. [PMID: 31379355 DOI: 10.1088/1361-648x/ab31f4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We explore the scattering of Dirac electrons in a double-gated topological insulator in the presence of magnetic proximity effects and warped surface states. It is found that a magnetic field can shift the Dirac cone in momentum space and deform the constant-energy contour, or opens up a band gap at the Dirac point, depending on the magnetization orientation. The double gate voltage induces quantum wells and/or quantum barriers on the surface of topological insulators, generating surface resonant tunnelling states. It is found that the hexagonal warping effect can increase the electronic transport at high energies when the constant-energy contour exhibits a snowflake shape. The energy-dependent conductances in the parallel and antiparallel magnetic configurations exhibit out-of-phase oscillations due to the quantum interference of propagating waves in the region between the two magnetized segments. Although the conductance spectrum of the double-well structure is higher than that of the double-barrier structure, the magnetoresistance ratio versus the separation distance between the two magnetized barriers exhibits pronounced oscillations due to the resonant tunnelling states. We show that the surface state transport can be controlled by the exchange field and gate voltage without breaking time reversal symmetry, suggesting that the double gated and magnetized topological insulators can be utilized to achieve a large magnetoresistance ratio with a tunable sign.
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Affiliation(s)
- Masomeh Arabikhah
- Department of Physics, Payame Noor University, PO Box 19395-3697 Tehran, Iran
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26
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Wu H, Xu Y, Deng P, Pan Q, Razavi SA, Wong K, Huang L, Dai B, Shao Q, Yu G, Han X, Rojas-Sánchez JC, Mangin S, Wang KL. Spin-Orbit Torque Switching of a Nearly Compensated Ferrimagnet by Topological Surface States. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1901681. [PMID: 31282067 DOI: 10.1002/adma.201901681] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2019] [Revised: 05/07/2019] [Indexed: 06/09/2023]
Abstract
Utilizing spin-orbit torque (SOT) to switch a magnetic moment provides a promising route for low-power-dissipation spintronic devices. Here, the SOT switching of a nearly compensated ferrimagnet Gdx (FeCo)1- x by the topological insulator [Bi2 Se3 and (BiSb)2 Te3 ] is investigated at room temperature. The switching current density of (BiSb)2 Te3 (1.20 × 105 A cm-2 ) is more than one order of magnitude smaller than that in conventional heavy-metal-based structures, which indicates the ultrahigh efficiency of charge-spin conversion (>1) in topological surface states. By tuning the net magnetic moment of Gdx (FeCo)1- x via changing the composition, the SOT efficiency has a significant enhancement (6.5 times) near the magnetic compensation point, and at the same time the switching speed can be as fast as several picoseconds. Combining the topological surface states and the nearly compensated ferrimagnets provides a promising route for practical energy-efficient and high-speed spintronic devices.
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Affiliation(s)
- Hao Wu
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095, USA
| | - Yong Xu
- Institut Jean Lamour, CNRS UMR 7198, Université de Lorraine, Nancy, F-54500, France
| | - Peng Deng
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095, USA
| | - Quanjun Pan
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095, USA
| | - Seyed Armin Razavi
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095, USA
| | - Kin Wong
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095, USA
| | - Li Huang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Bingqian Dai
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095, USA
| | - Qiming Shao
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095, USA
| | - Guoqiang Yu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Xiufeng Han
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | | | - Stéphane Mangin
- Institut Jean Lamour, CNRS UMR 7198, Université de Lorraine, Nancy, F-54500, France
| | - Kang L Wang
- Department of Electrical and Computer Engineering, and Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095, USA
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27
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Li P, Kally J, Zhang SSL, Pillsbury T, Ding J, Csaba G, Ding J, Jiang JS, Liu Y, Sinclair R, Bi C, DeMann A, Rimal G, Zhang W, Field SB, Tang J, Wang W, Heinonen OG, Novosad V, Hoffmann A, Samarth N, Wu M. Magnetization switching using topological surface states. SCIENCE ADVANCES 2019; 5:eaaw3415. [PMID: 31497642 PMCID: PMC6716955 DOI: 10.1126/sciadv.aaw3415] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Accepted: 07/31/2019] [Indexed: 05/19/2023]
Abstract
Topological surface states (TSSs) in a topological insulator are expected to be able to produce a spin-orbit torque that can switch a neighboring ferromagnet. This effect may be absent if the ferromagnet is conductive because it can completely suppress the TSSs, but it should be present if the ferromagnet is insulating. This study reports TSS-induced switching in a bilayer consisting of a topological insulator Bi2Se3 and an insulating ferromagnet BaFe12O19. A charge current in Bi2Se3 can switch the magnetization in BaFe12O19 up and down. When the magnetization is switched by a field, a current in Bi2Se3 can reduce the switching field by ~4000 Oe. The switching efficiency at 3 K is 300 times higher than at room temperature; it is ~30 times higher than in Pt/BaFe12O19. These strong effects originate from the presence of more pronounced TSSs at low temperatures due to enhanced surface conductivity and reduced bulk conductivity.
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Affiliation(s)
- Peng Li
- Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
| | - James Kally
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Steven S.-L. Zhang
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Timothy Pillsbury
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Jinjun Ding
- Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
| | - Gyorgy Csaba
- Faculty of Information Technology and Bionics, Pazmany Peter Catholic University, Budapest, Hungary
| | - Junjia Ding
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - J. S. Jiang
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Yunzhi Liu
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
| | - Robert Sinclair
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
| | - Chong Bi
- Department of Physics, University of Arizona, Tucson, AZ 85721, USA
| | - August DeMann
- Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
| | - Gaurab Rimal
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
| | - Wei Zhang
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
- Department of Physics, Oakland University, Rochester, MI 48309, USA
| | - Stuart B. Field
- Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
| | - Jinke Tang
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
| | - Weigang Wang
- Department of Physics, University of Arizona, Tucson, AZ 85721, USA
| | - Olle G. Heinonen
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Valentine Novosad
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Axel Hoffmann
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Nitin Samarth
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Mingzhong Wu
- Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
- Corresponding author.
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28
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He P, Zhang SSL, Zhu D, Shi S, Heinonen OG, Vignale G, Yang H. Nonlinear Planar Hall Effect. PHYSICAL REVIEW LETTERS 2019; 123:016801. [PMID: 31386424 DOI: 10.1103/physrevlett.123.016801] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Revised: 05/07/2019] [Indexed: 06/10/2023]
Abstract
An intriguing property of a three-dimensional (3D) topological insulator (TI) is the existence of surface states with spin-momentum locking, which offers a new frontier of exploration in spintronics. Here, we report the observation of a new type of Hall effect in a 3D TI Bi_{2}Se_{3} film. The Hall resistance scales linearly with both the applied electric and magnetic fields and exhibits a π/2 angle offset with respect to its longitudinal counterpart, in contrast to the usual angle offset of π/4 between the linear planar Hall effect and the anisotropic magnetoresistance. This novel nonlinear planar Hall effect originates from the conversion of a nonlinear transverse spin current to a charge current due to the concerted actions of spin-momentum locking and time-reversal symmetry breaking, which also exists in a wide class of noncentrosymmetric materials with a large span of magnitude. It provides a new way to characterize and utilize the nonlinear spin-to-charge conversion in a variety of topological quantum materials.
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Affiliation(s)
- Pan He
- Department of Electrical and Computer Engineering, and NUSNNI, National University of Singapore, 117576 Singapore
| | - Steven S-L Zhang
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
| | - Dapeng Zhu
- Department of Electrical and Computer Engineering, and NUSNNI, National University of Singapore, 117576 Singapore
| | - Shuyuan Shi
- Department of Electrical and Computer Engineering, and NUSNNI, National University of Singapore, 117576 Singapore
| | - Olle G Heinonen
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Giovanni Vignale
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
| | - Hyunsoo Yang
- Department of Electrical and Computer Engineering, and NUSNNI, National University of Singapore, 117576 Singapore
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29
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Fan Y, Shao Q, Pan L, Che X, He Q, Yin G, Zheng C, Yu G, Nie T, Masir MR, MacDonald AH, Wang KL. Unidirectional Magneto-Resistance in Modulation-Doped Magnetic Topological Insulators. NANO LETTERS 2019; 19:692-698. [PMID: 30685979 DOI: 10.1021/acs.nanolett.8b03702] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Nonlinear unidirectional spin Hall magnetoresistance (USMR) has been reported in heavy metal/ferromagnet bilayers, which could be employed as an effective method in detecting the magnetization orientation in spintronic devices with two-terminal geometry. Recently, another unidirectional magnetoresistance (UMR) was reported in magnetic topological insulator (TI)-based heterostructures at cryogenic temperature, whose amplitude is orders of magnitude larger than the USMR measured in heavy metal-based magnetic heterostructures at room temperature. Here, we report the UMR effect in the modulation-doped magnetic TI structures. This UMR arises due to the interplay between the magnetic dopant's magnetization and the current-induced surface spin polarization, when they are parallel or antiparallel to each other in the TI material. By varying the dopant's position in the structure, we reveal that the UMR is mainly originating from the interaction between the magnetization and the surface spin-polarized carriers (not bulk carriers). Furthermore, from the magnetic field-, the angular rotation-, and the temperature-dependence, we highlight the correlation between the UMR effect and the magnetism in the structures. The large UMR versus current ratio in TI-based magnetic bilayers promises the easy readout in TI-based spintronic devices with two-terminal geometry.
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Affiliation(s)
- Yabin Fan
- Department of Electrical and Computer Engineering , University of California , Los Angeles , California 90095 , United States
- Microsystems Technology Laboratories , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - Qiming Shao
- Department of Electrical and Computer Engineering , University of California , Los Angeles , California 90095 , United States
| | - Lei Pan
- Department of Electrical and Computer Engineering , University of California , Los Angeles , California 90095 , United States
| | - Xiaoyu Che
- Department of Electrical and Computer Engineering , University of California , Los Angeles , California 90095 , United States
| | - Qinglin He
- Department of Electrical and Computer Engineering , University of California , Los Angeles , California 90095 , United States
| | - Gen Yin
- Department of Electrical and Computer Engineering , University of California , Los Angeles , California 90095 , United States
| | - Cheng Zheng
- Department of Electrical and Computer Engineering , University of California , Los Angeles , California 90095 , United States
| | - Guoqiang Yu
- Department of Electrical and Computer Engineering , University of California , Los Angeles , California 90095 , United States
| | - Tianxiao Nie
- Fert Beijing Institute, BDBC, and School of Electronic and Information Engineering , Beihang University , Beijing 100191 , China
| | - Massoud R Masir
- Department of Physics and Center for Complex Quantum Systems , University of Texas at Austin , Austin , Texas 78712-0264 , United States
| | - Allan H MacDonald
- Department of Physics and Center for Complex Quantum Systems , University of Texas at Austin , Austin , Texas 78712-0264 , United States
| | - Kang L Wang
- Department of Electrical and Computer Engineering , University of California , Los Angeles , California 90095 , United States
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30
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Yoshimi R, Yasuda K, Tsukazaki A, Takahashi KS, Kawasaki M, Tokura Y. Current-driven magnetization switching in ferromagnetic bulk Rashba semiconductor (Ge,Mn)Te. SCIENCE ADVANCES 2018; 4:eaat9989. [PMID: 30539144 PMCID: PMC6286171 DOI: 10.1126/sciadv.aat9989] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 11/06/2018] [Indexed: 06/09/2023]
Abstract
Multiferroic materials with both ferroelectric and ferromagnetic orders provide a promising arena for the electrical manipulation of magnetization through the mutual correlation between those ferroic orders. Such a concept of multiferroics may expand to semiconductor with both broken symmetries of spatial inversion and time reversal, that is, polar ferromagnetic semiconductors. Here, we report the observation of current-driven magnetization switching in one such example, (Ge,Mn)Te thin films. The ferromagnetism caused by Mn doping opens an exchange gap in original massless Dirac band of the polar semiconductor GeTe with Rashba-type spin-split bands. The anomalous Hall conductivity is enhanced with increasing hole carrier density, indicating that the contribution of the Berry phase is maximized as the Fermi level approaches the exchange gap. By means of pulse-current injection, the electrical switching of the magnetization is observed in the (Ge,Mn)Te thin films as thick as 200 nm, pointing to the Rashba-Edelstein effect of bulk origin. The efficiency of this effect strongly depends on the Fermi-level position owing to the efficient spin accumulation at around the gap. The magnetic bulk Rashba system will be a promising platform for exploring the functional correlations among electric polarization, magnetization, and current.
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Affiliation(s)
- R. Yoshimi
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - K. Yasuda
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656, Japan
| | - A. Tsukazaki
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - K. S. Takahashi
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
- PRESTO, Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0075, Japan
| | - M. Kawasaki
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656, Japan
| | - Y. Tokura
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656, Japan
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31
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Wang X, Cheng L, Zhu D, Wu Y, Chen M, Wang Y, Zhao D, Boothroyd CB, Lam YM, Zhu JX, Battiato M, Song JCW, Yang H, Chia EEM. Ultrafast Spin-to-Charge Conversion at the Surface of Topological Insulator Thin Films. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1802356. [PMID: 30370615 DOI: 10.1002/adma.201802356] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Revised: 09/20/2018] [Indexed: 06/08/2023]
Abstract
Strong spin-orbit coupling, resulting in the formation of spin-momentum-locked surface states, endows topological insulators with superior spin-to-charge conversion characteristics, though the dynamics that govern it have remained elusive. Here, an all-optical method is presented, which enables unprecedented tracking of the ultrafast dynamics of spin-to-charge conversion in a prototypical topological insulator Bi2 Se3 /ferromagnetic Co heterostructure, down to the sub-picosecond timescale. Compared to pure Bi2 Se3 or Co, a giant terahertz emission is observed in the heterostructure that originates from spin-to-charge conversion, in which the topological surface states play a crucial role. A 0.12 ps timescale is identified that sets a technological speed limit of spin-to-charge conversion processes in topological insulators. In addition, it is shown that the spin-to-charge conversion efficiency is temperature independent in Bi2 Se3 as expected from the nature of the surface states, paving the way for designing next-generation high-speed optospintronic devices based on topological insulators at room temperature.
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Affiliation(s)
- Xinbo Wang
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Liang Cheng
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Dapeng Zhu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Yang Wu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Mengji Chen
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Yi Wang
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Daming Zhao
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Chris B Boothroyd
- School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Yeng Ming Lam
- School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Jian-Xin Zhu
- Theoretical Division and Center for Integrated Nanotechnologies, Los Alamos National Laboratory, NM, 87545, USA
| | - Marco Battiato
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
- Institute of Solid State Physics, Vienna University of Technology, 1040, Vienna, Austria
| | - Justin C W Song
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
- Institute of High Performance Computing, Agency for Science, Technology, and Research, Singapore, 138632, Singapore
| | - Hyunsoo Yang
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Elbert E M Chia
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
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32
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Spin-momentum locking and spin-orbit torques in magnetic nano-heterojunctions composed of Weyl semimetal WTe 2. Nat Commun 2018; 9:3990. [PMID: 30266960 PMCID: PMC6162210 DOI: 10.1038/s41467-018-06518-1] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2018] [Accepted: 09/10/2018] [Indexed: 11/23/2022] Open
Abstract
Spin–orbit torque has recently been intensively investigated for the purposes of manipulating the magnetization in magnetic nano-devices and understanding fundamental physics. Therefore, the search for novel materials or material combinations that exhibit a strong enough spin-torque effect has become one of the top priorities in this field of spintronics. Weyl semimetal, a new topological material that features open Fermi arc with strong spin–orbit coupling and spin–momentum locking effect, is naturally expected to exhibit an enhanced spin-torque effect in magnetic nano-devices. Here we observe a significantly enhanced spin conductivity, which is associated with the field-like torque at low temperatures. The enhancement is obtained in the b-axis WTe2/Py bilayers of nano-devices but not observed in the a-axis of WTe2/Py nano-devices, which can be ascribed to the enhanced spin accumulation by the spin–momentum locking effect of the Fermi arcs of the Weyl semimetal WTe2. The Fermi arcs, topological surface states of Weyl semimetals can enable the intriguing spin control and facilitate topological spintronics. Here the authors report the spin-orbit torque at the interface of WTe2/Py and attribute it to the enhanced spin accumulation by the spin-momentum locking effect of the Fermi arcs of WTe2.
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33
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Avci CO, Mendil J, Beach GSD, Gambardella P. Origins of the Unidirectional Spin Hall Magnetoresistance in Metallic Bilayers. PHYSICAL REVIEW LETTERS 2018; 121:087207. [PMID: 30192570 DOI: 10.1103/physrevlett.121.087207] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Indexed: 06/08/2023]
Abstract
Recent studies evidenced the emergence of asymmetric electron transport in layered conductors owing to the interplay between electrical conductivity, magnetization, and the spin Hall or Rashba-Edelstein effects. Here, we investigate the unidirectional magnetoresistance (UMR) caused by the current-induced spin accumulation in Co/Pt and CoCr/Pt bilayers. We identify three competing mechanisms underpinning the resistance asymmetry, namely, interface and bulk spin-dependent electron scattering and electron-magnon scattering. Our measurements provide a consistent description of the current, magnetic field, and temperature dependence of the UMR and show that both positive and negative UMR can be obtained by tuning the interface and bulk spin-dependent scattering.
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Affiliation(s)
- Can Onur Avci
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Johannes Mendil
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - Geoffrey S D Beach
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Yokouchi T, Hoshino S, Kanazawa N, Kikkawa A, Morikawa D, Shibata K, Arima TH, Taguchi Y, Kagawa F, Nagaosa N, Tokura Y. Current-induced dynamics of skyrmion strings. SCIENCE ADVANCES 2018; 4:eaat1115. [PMID: 30105304 PMCID: PMC6086615 DOI: 10.1126/sciadv.aat1115] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Accepted: 06/29/2018] [Indexed: 05/29/2023]
Abstract
Dynamics of string-like objects is an important issue in a broad range of physical systems, including vortex lines in superconductors, viscoelastic polymers, and superstrings in elementary particle physics. In noncentrosymmetric magnets, string forms of magnetic skyrmions are present as topological spin objects, and their current-induced dynamics has recently attracted intense interest. We show in the chiral magnet MnSi that the current-induced deformation dynamics of skyrmion strings results in transport response associated with the real-space Berry phase. Prominent nonlinear Hall signals emerge above the threshold current only in the skyrmion phase. We clarify the mechanism for these nonlinear Hall signals by adopting spin density wave picture to describe the moving skyrmion lattice; deformation of skyrmion strings occurs in an asymmetric manner due to the Dzyaloshinskii-Moriya interaction, which leads to the nonreciprocal nonlinear Hall response originating from an emergent electromagnetic field. This finding reveals the dynamical nature of string-like objects and consequent transport outcomes in noncentrosymmetric systems.
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Affiliation(s)
- Tomoyuki Yokouchi
- Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
| | | | - Naoya Kanazawa
- Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
| | - Akiko Kikkawa
- RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
| | | | - Kiyou Shibata
- RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
| | - Taka-hisa Arima
- RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
- Department of Advanced Materials Science, The University of Tokyo, Kashiwa 277-8561, Japan
| | | | - Fumitaka Kagawa
- RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
| | - Naoto Nagaosa
- Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
- RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
| | - Yoshinori Tokura
- Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
- RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
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Wang X, Wan C, Kong W, Zhang X, Xing Y, Fang C, Tao B, Yang W, Huang L, Wu H, Irfan M, Han X. Field-Free Programmable Spin Logics via Chirality-Reversible Spin-Orbit Torque Switching. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1801318. [PMID: 29931713 DOI: 10.1002/adma.201801318] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 05/15/2018] [Indexed: 06/08/2023]
Abstract
Spin-orbit torque (SOT)-induced magnetization switching exhibits chirality (clockwise or counterclockwise), which offers the prospect of programmable spin-logic devices integrating nonvolatile spintronic memory cells with logic functions. Chirality is usually fixed by an applied or effective magnetic field in reported studies. Herein, utilizing an in-plane magnetic layer that is also switchable by SOT, the chirality of a perpendicular magnetic layer that is exchange-coupled with the in-plane layer can be reversed in a purely electrical way. In a single Hall bar device designed from this multilayer structure, three logic gates including AND, NAND, and NOT are reconfigured, which opens a gateway toward practical programmable spin-logic devices.
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Affiliation(s)
- Xiao Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Caihua Wan
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Wenjie Kong
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Xuan Zhang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Yaowen Xing
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Chi Fang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Bingshan Tao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Wenlong Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Li Huang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Hao Wu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Muhammad Irfan
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
| | - Xiufeng Han
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, China
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36
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Liu Y, Besbas J, Wang Y, He P, Chen M, Zhu D, Wu Y, Lee JM, Wang L, Moon J, Koirala N, Oh S, Yang H. Direct visualization of current-induced spin accumulation in topological insulators. Nat Commun 2018; 9:2492. [PMID: 29950680 PMCID: PMC6021425 DOI: 10.1038/s41467-018-04939-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2017] [Accepted: 06/07/2018] [Indexed: 11/08/2022] Open
Abstract
Charge-to-spin conversion in various materials is the key for the fundamental understanding of spin-orbitronics and efficient magnetization manipulation. Here we report the direct spatial imaging of current-induced spin accumulation at the channel edges of Bi2Se3 and BiSbTeSe2 topological insulators as well as Pt by a scanning photovoltage microscope at room temperature. The spin polarization is along the out-of-plane direction with opposite signs for the two channel edges. The accumulated spin direction reverses sign upon changing the current direction and the detected spin signal shows a linear dependence on the magnitude of currents, indicating that our observed phenomena are current-induced effects. The spin Hall angle of Bi2Se3, BiSbTeSe2, and Pt is determined to be 0.0085, 0.0616, and 0.0085, respectively. Our results open up the possibility of optically detecting the current-induced spin accumulations, and thus point towards a better understanding of the interaction between spins and circularly polarized light.
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Affiliation(s)
- Yang Liu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Jean Besbas
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Yi Wang
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Pan He
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Mengji Chen
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Dapeng Zhu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Yang Wu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Jong Min Lee
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore
| | - Lan Wang
- RMIT University, School of Science, Department of Physics, Melbourne, VIC, 3001, Australia
| | - Jisoo Moon
- Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ, 08854, USA
| | - Nikesh Koirala
- Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ, 08854, USA
| | - Seongshik Oh
- Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ, 08854, USA
| | - Hyunsoo Yang
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore.
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Yasuda K, Mogi M, Yoshimi R, Tsukazaki A, Takahashi KS, Kawasaki M, Kagawa F, Tokura Y. Quantized chiral edge conduction on domain walls of a magnetic topological insulator. Science 2018; 358:1311-1314. [PMID: 29217573 DOI: 10.1126/science.aan5991] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2017] [Accepted: 10/24/2017] [Indexed: 11/02/2022]
Abstract
Electronic ordering in magnetic and dielectric materials forms domains with different signs of order parameters. The control of configuration and motion of the domain walls (DWs) enables nonvolatile responses against minute external fields. Here, we realize chiral edge states (CESs) on the magnetic DWs of a magnetic topological insulator. We design and fabricate the magnetic domains in the quantum anomalous Hall state with the tip of a magnetic force microscope and prove the existence of the chiral one-dimensional edge conduction along the prescribed DWs through transport measurements. The proof-of-concept devices based on reconfigurable CESs and Landauer-Büttiker formalism are realized for multiple-domain configurations with well-defined DW channels. Our results may lead to the realization of low-power-consumption spintronic devices.
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Affiliation(s)
- K Yasuda
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656, Japan
| | - M Mogi
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656, Japan
| | - R Yoshimi
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - A Tsukazaki
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - K S Takahashi
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.,Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0075, Japan
| | - M Kawasaki
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656, Japan.,RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - F Kagawa
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - Y Tokura
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656, Japan.,RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
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38
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Mogi M, Kawamura M, Tsukazaki A, Yoshimi R, Takahashi KS, Kawasaki M, Tokura Y. Tailoring tricolor structure of magnetic topological insulator for robust axion insulator. SCIENCE ADVANCES 2017; 3:eaao1669. [PMID: 28989967 PMCID: PMC5630236 DOI: 10.1126/sciadv.aao1669] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Accepted: 09/15/2017] [Indexed: 05/23/2023]
Abstract
Exploration of novel electromagnetic phenomena is a subject of great interest in topological quantum materials. One of the unprecedented effects to be experimentally verified is the topological magnetoelectric (TME) effect originating from an unusual coupling of electric and magnetic fields in materials. A magnetic heterostructure of topological insulator (TI) hosts such exotic magnetoelectric coupling and can be expected to realize the TME effect as an axion insulator. We designed a magnetic TI with a tricolor structure where a nonmagnetic layer of (Bi, Sb)2Te3 is sandwiched by a soft ferromagnetic Cr-doped (Bi, Sb)2Te3 and a hard ferromagnetic V-doped (Bi, Sb)2Te3. Accompanied by the quantum anomalous Hall (QAH) effect, we observe zero Hall conductivity plateaus, which are a hallmark of the axion insulator state, in a wide range of magnetic fields between the coercive fields of Cr- and V-doped layers. The resistance of the axion insulator state reaches as high as 109 ohms, leading to a gigantic magnetoresistance ratio exceeding 10,000,000% upon the transition from the QAH state. The tricolor structure of the TI may not only be an ideal arena for the topologically distinct phenomena but can also provide magnetoresistive applications for advancing dissipation-less topological electronics.
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Affiliation(s)
- Masataka Mogi
- Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Minoru Kawamura
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
| | - Atsushi Tsukazaki
- Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan
| | - Ryutaro Yoshimi
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
| | - Kei S. Takahashi
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
- PRESTO, Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0075, Japan
| | - Masashi Kawasaki
- Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
| | - Yoshinori Tokura
- Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
- RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
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