1
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Zhang Y, Tian H, Li H, Yoon C, Nelson RA, Li Z, Watanabe K, Taniguchi T, Smirnov D, Kawakami RK, Goldberger JE, Zhang F, Lau CN. Quantum octets in high mobility pentagonal two-dimensional PdSe 2. Nat Commun 2024; 15:761. [PMID: 38278796 PMCID: PMC10817936 DOI: 10.1038/s41467-024-44972-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Accepted: 01/11/2024] [Indexed: 01/28/2024] Open
Abstract
Two-dimensional (2D) materials have drawn immense interests in scientific and technological communities, owing to their extraordinary properties and their tunability by gating, proximity, strain and external fields. For electronic applications, an ideal 2D material would have high mobility, air stability, sizable band gap, and be compatible with large scale synthesis. Here we demonstrate air stable field effect transistors using atomically thin few-layer PdSe2 sheets that are sandwiched between hexagonal BN (hBN), with large saturation current > 350 μA/μm, and high field effect mobilities of ~ 700 and 10,000 cm2/Vs at 300 K and 2 K, respectively. At low temperatures, magnetotransport studies reveal unique octets in quantum oscillations that persist at all densities, arising from 2-fold spin and 4-fold valley degeneracies, which can be broken by in-plane and out-of-plane magnetic fields toward quantum Hall spin and orbital ferromagnetism.
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Affiliation(s)
- Yuxin Zhang
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
| | - Haidong Tian
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
| | - Huaixuan Li
- Department of Physics, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080-3021, USA
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Chiho Yoon
- Department of Physics, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080-3021, USA
| | - Ryan A Nelson
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210, USA
| | - Ziling Li
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Dmitry Smirnov
- National High Magnetic Field Laboratory, Tallahassee, FL, 32310, USA
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
| | - Joshua E Goldberger
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210, USA
| | - Fan Zhang
- Department of Physics, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080-3021, USA
| | - Chun Ning Lau
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA.
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2
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Lyalin I, Alikhah S, Berritta M, Oppeneer PM, Kawakami RK. Magneto-Optical Detection of the Orbital Hall Effect in Chromium. Phys Rev Lett 2023; 131:156702. [PMID: 37897779 DOI: 10.1103/physrevlett.131.156702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Accepted: 09/07/2023] [Indexed: 10/30/2023]
Abstract
The orbital Hall effect has been theoretically predicted but its direct observation is a challenge. Here, we report the magneto-optical detection of current-induced orbital accumulation at the surface of a light 3d transition metal, Cr. The orbital polarization is in-plane, transverse to the current direction, and scales linearly with current density, consistent with the orbital Hall effect. Comparing the thickness-dependent magneto-optical measurements with ab initio calculations, we estimate an orbital diffusion length in Cr of 6.6±0.6 nm.
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Affiliation(s)
- Igor Lyalin
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Sanaz Alikhah
- Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-75120 Uppsala, Sweden
| | - Marco Berritta
- Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-75120 Uppsala, Sweden
- Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, United Kingdom
| | - Peter M Oppeneer
- Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-75120 Uppsala, Sweden
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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3
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Cheng S, Nrisimhamurty M, Zhou T, Bagués N, Zhou W, Bishop AJ, Lyalin I, Jozwiak C, Bostwick A, Rotenberg E, McComb DW, Žutić I, Kawakami RK. Epitaxial Kagome Thin Films as a Platform for Topological Flat Bands. Nano Lett 2023; 23:7107-7113. [PMID: 37506350 DOI: 10.1021/acs.nanolett.3c01961] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/30/2023]
Abstract
Systems with flat bands are ideal for studying strongly correlated electronic states and related phenomena. Among them, kagome-structured metals such as CoSn have been recognized as promising candidates due to the proximity between the flat bands and the Fermi level. A key next step will be to realize epitaxial kagome thin films with flat bands to enable tuning of the flat bands across the Fermi level via electrostatic gating or strain. Here, we report the band structures of epitaxial CoSn thin films grown directly on the insulating substrates. Flat bands are observed by using synchrotron-based angle-resolved photoemission spectroscopy (ARPES). The band structure is consistent with density functional theory (DFT) calculations, and the transport properties are quantitatively explained by the band structure and semiclassical transport theory. Our work paves the way to realize flat band-induced phenomena through fine-tuning of flat bands in kagome materials.
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Affiliation(s)
- Shuyu Cheng
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - M Nrisimhamurty
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Tong Zhou
- Department of Physics, University at Buffalo, Buffalo, New York 14260, United States
| | - Núria Bagués
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, United States
| | - Wenyi Zhou
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Alexander J Bishop
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Igor Lyalin
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Chris Jozwiak
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Aaron Bostwick
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Eli Rotenberg
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - David W McComb
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, United States
| | - Igor Žutić
- Department of Physics, University at Buffalo, Buffalo, New York 14260, United States
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
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4
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Kunin A, Chernov S, Bakalis J, Li Z, Cheng S, Withers ZH, White MG, Schönhense G, Du X, Kawakami RK, Allison TK. Momentum-Resolved Exciton Coupling and Valley Polarization Dynamics in Monolayer WS_{2}. Phys Rev Lett 2023; 130:046202. [PMID: 36763432 DOI: 10.1103/physrevlett.130.046202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Accepted: 12/22/2022] [Indexed: 06/18/2023]
Abstract
Using time- and angle-resolved photoemission, we present momentum- and energy-resolved measurements of exciton coupling in monolayer WS_{2}. We observe strong intravalley coupling between the B_{1s} exciton and A_{n>1} states. Our measurements indicate that the dominant valley depolarization mechanism conserves the exciton binding energy and momentum. While this conservation is consistent with Coulomb exchange-driven valley depolarization, we do not observe a momentum or energy dependence to the depolarization rate as would be expected for the exchange-based mechanism.
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Affiliation(s)
- Alice Kunin
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
| | - Sergey Chernov
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
| | - Jin Bakalis
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
| | - Ziling Li
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Shuyu Cheng
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Zachary H Withers
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
| | - Michael G White
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Gerd Schönhense
- Johannes Gutenberg-Universität, Institut für Physik, D-55099 Mainz, Germany
| | - Xu Du
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Thomas K Allison
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
- Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
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5
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Repicky J, Wu PK, Liu T, Corbett JP, Zhu T, Cheng S, Ahmed AS, Takeuchi N, Guerrero-Sanchez J, Randeria M, Kawakami RK, Gupta JA. Atomic-scale visualization of topological spin textures in the chiral magnet MnGe. Science 2021; 374:1484-1487. [PMID: 34914516 DOI: 10.1126/science.abd9225] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
[Figure: see text].
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Affiliation(s)
- Jacob Repicky
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Po-Kuan Wu
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Tao Liu
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA.,University of Electronic Science and Technology of China, Chengdu 610054, China
| | - Joseph P Corbett
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Tiancong Zhu
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Shuyu Cheng
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Adam S Ahmed
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - N Takeuchi
- Centro de Nanociencias y Nanotecnologia, Universidad Nacional Autónoma de México, Apartado Postal 14, Ensenada Baja California, Código Postal 22800, Mexico
| | - J Guerrero-Sanchez
- Centro de Nanociencias y Nanotecnologia, Universidad Nacional Autónoma de México, Apartado Postal 14, Ensenada Baja California, Código Postal 22800, Mexico
| | - Mohit Randeria
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Jay A Gupta
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
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6
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Wang B, Bagués N, Liu T, Kawakami RK, McComb DW. Extracting weak magnetic contrast from complex background contrast in plan-view FeGe thin films. Ultramicroscopy 2021; 232:113395. [PMID: 34653891 DOI: 10.1016/j.ultramic.2021.113395] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 09/07/2021] [Accepted: 09/20/2021] [Indexed: 11/29/2022]
Abstract
The desire to design and build skyrmion-based devices has led to the need to characterize magnetic textures in thin films of functional materials. This can usually be achieved through the Lorentz transmission electron microscopy (LTEM) and the Lorentz scanning transmission electron microscopy (LSTEM) in thin film cross-section and single crystal specimens. However, direct imaging of the magnetic texture in plan-view samples of thin (< 50 nm) films has proved to be challenging due to the complex "background" contrast associated with the microstructure and defects, as well as contributions from bending of the specimens. Using a mechanically polished 35 nm plan-view FeGe thin film, we have explored three methods to extract magnetic contrast from the complex background contrast observed; (1) background subtraction in defocused LTEM images, (2) frequency filtered CoM-DPC reconstructed from LSTEM datasets and 3) registration of 4D-STEM datasets acquired at different tilt angles. Using these methods, we have successfully implemented real space imaging of both the helical phase and skyrmion phase. The ability to understand nanoscale magnetic behavior from plan-view thin films is a fundamental step towards development of highly integrated spin electronics.
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Affiliation(s)
- Binbin Wang
- Department of Materials Science and Engineering, The Ohio State University, OH 43210, United States; Center for Electron Microscopy and Analysis, The Ohio State University, OH 43212, United States.
| | - Núria Bagués
- Center for Electron Microscopy and Analysis, The Ohio State University, OH 43212, United States
| | - Tao Liu
- Department of Physics, The Ohio State University, OH 43212, United States
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, OH 43212, United States
| | - David W McComb
- Department of Materials Science and Engineering, The Ohio State University, OH 43210, United States; Center for Electron Microscopy and Analysis, The Ohio State University, OH 43212, United States.
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7
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Lyalin I, Cheng S, Kawakami RK. Spin-Orbit Torque in Bilayers of Kagome Ferromagnet Fe 3Sn 2 and Pt. Nano Lett 2021; 21:6975-6982. [PMID: 34380320 DOI: 10.1021/acs.nanolett.1c02270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Spin-orbit torque phenomena enable efficient manipulation of the magnetization in ferromagnet/heavy metal bilayer systems for prospective magnetic memory and logic applications. Kagome magnets are of particular interest for spin-orbit torque due to the interplay of magnetic order and the nontrivial band topology (e.g., flat bands and Dirac and Weyl points). Here we demonstrate spin-orbit torque and quantify its efficiency in a bilayer system of topological kagome ferromagnet Fe3Sn2 and platinum. We use two different techniques, one based on the quasistatic magneto-optic Kerr effect (MOKE) and another based on time-resolved MOKE, to quantify spin-orbit torque. Both techniques give a consistent value of the effective spin Hall angle of the Fe3Sn2/Pt system. Our work may lead to further advances in spintronics based on topological kagome magnets.
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Affiliation(s)
- Igor Lyalin
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Shuyu Cheng
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
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8
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Sierra JF, Fabian J, Kawakami RK, Roche S, Valenzuela SO. Van der Waals heterostructures for spintronics and opto-spintronics. Nat Nanotechnol 2021; 16:856-868. [PMID: 34282312 DOI: 10.1038/s41565-021-00936-x] [Citation(s) in RCA: 97] [Impact Index Per Article: 32.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 06/03/2021] [Indexed: 06/13/2023]
Abstract
The large variety of 2D materials and their co-integration in van der Waals heterostructures enable innovative device engineering. In addition, their atomically thin nature promotes the design of artificial materials by proximity effects that originate from short-range interactions. Such a designer approach is particularly compelling for spintronics, which typically harnesses functionalities from thin layers of magnetic and non-magnetic materials and the interfaces between them. Here we provide an overview of recent progress in 2D spintronics and opto-spintronics using van der Waals heterostructures. After an introduction to the forefront of spin transport research, we highlight the unique spin-related phenomena arising from spin-orbit and magnetic proximity effects. We further describe the ability to create multifunctional hybrid heterostructures based on van der Waals materials, combining spin, valley and excitonic degrees of freedom. We end with an outlook on perspectives and challenges for the design and production of ultracompact all-2D spin devices and their potential applications in conventional and quantum technologies.
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Affiliation(s)
- Juan F Sierra
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology (BIST), Barcelona, Spain.
| | - Jaroslav Fabian
- Institute for Theoretical Physics, University of Regensburg, Regensburg, Germany
| | | | - Stephan Roche
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology (BIST), Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
| | - Sergio O Valenzuela
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology (BIST), Barcelona, Spain.
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain.
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9
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Zhu T, Bishop AJ, Zhou T, Zhu M, O'Hara DJ, Baker AA, Cheng S, Walko RC, Repicky JJ, Liu T, Gupta JA, Jozwiak CM, Rotenberg E, Hwang J, Žutić I, Kawakami RK. Synthesis, Magnetic Properties, and Electronic Structure of Magnetic Topological Insulator MnBi 2Se 4. Nano Lett 2021; 21:5083-5090. [PMID: 34097421 DOI: 10.1021/acs.nanolett.1c00141] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The intrinsic magnetic topological insulators MnBi2Te4 and MnBi2Se4 support novel topological states related to symmetry breaking by magnetic order. Unlike MnBi2Te4, the study of MnBi2Se4 has been inhibited by the lack of bulk crystals, as the van der Waals (vdW) crystal is not the thermodynamic equilibrium phase. Here, we report the layer-by-layer synthesis of vdW MnBi2Se4 crystals using nonequilibrium molecular beam epitaxy. Atomic-resolution scanning transmission electron microscopy and scanning tunneling microscopy identify a well-ordered vdW crystal with septuple-layer base units. The magnetic properties agree with the predicted layered antiferromagnetic ordering but disagree with its predicted out-of-plane orientation. Instead, our samples exhibit an easy-plane anisotropy, which is explained by including dipole-dipole interactions. Angle-resolved photoemission spectroscopy reveals the gapless Dirac-like surface state, which demonstrates that MnBi2Se4 is a topological insulator above the magnetic-ordering temperature. These studies show that MnBi2Se4 is a promising candidate for exploring rich topological phases of layered antiferromagnetic topological insulators.
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Affiliation(s)
- Tiancong Zhu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Alexander J Bishop
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Tong Zhou
- Department of Physics, University at Buffalo, Buffalo, New York 14260, United States
| | - Menglin Zhu
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, United States
| | - Dante J O'Hara
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
- Materials Science and Engineering, University of California, Riverside, California 92521, United States
| | - Alexander A Baker
- Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Shuyu Cheng
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Robert C Walko
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Jacob J Repicky
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Tao Liu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Jay A Gupta
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Chris M Jozwiak
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Eli Rotenberg
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Jinwoo Hwang
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, United States
| | - Igor Žutić
- Department of Physics, University at Buffalo, Buffalo, New York 14260, United States
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
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10
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Corbett JP, Zhu T, Ahmed AS, Tjung SJ, Repicky JJ, Takeuchi T, Guerrero-Sanchez J, Takeuchi N, Kawakami RK, Gupta JA. Determining Surface Terminations and Chirality of Noncentrosymmetric FeGe Thin Films via Scanning Tunneling Microscopy. ACS Appl Mater Interfaces 2020; 12:9896-9901. [PMID: 31986007 DOI: 10.1021/acsami.9b19724] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Scanning tunneling microscopy was used to study the surfaces of 20-100 nm thick FeGe films grown by molecular beam epitaxy. An average surface lattice constant of ∼6.8 Å, in agreement with the bulk value, was observed via scanning tunneling microscopy, low energy electron diffraction, and reflection high energy electron diffraction. Each of the four possible chemical terminations in the FeGe films were identified by comparing atomic-resolution images, showing distinct contrast with simulations from density functional theory calculations. A detailed study of the atomic layering order and registry across step edges allows us to uniquely determine the grain orientation and chirality in these noncentrosymmetric films.
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Affiliation(s)
- Joseph P Corbett
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Tiancong Zhu
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Adam S Ahmed
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Steven J Tjung
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Jacob J Repicky
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Takahiro Takeuchi
- Integrated Graduate School of Medicine, Engineering, and Agricultural Science , University of Yamanashi , Kofu 400-8510 Japan
| | - Jonathan Guerrero-Sanchez
- Centro de Nanociencias y Nanotecnologia , Universidad Nacional Autónoma de México , Apartado Postal 14 , Ensenada , Baja California 22800 , Mexico
| | - Noboru Takeuchi
- Centro de Nanociencias y Nanotecnologia , Universidad Nacional Autónoma de México , Apartado Postal 14 , Ensenada , Baja California 22800 , Mexico
| | - Roland K Kawakami
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Jay A Gupta
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
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11
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Katoch J, Zhu T, Kochan D, Singh S, Fabian J, Kawakami RK. Transport Spectroscopy of Sublattice-Resolved Resonant Scattering in Hydrogen-Doped Bilayer Graphene. Phys Rev Lett 2018; 121:136801. [PMID: 30312090 DOI: 10.1103/physrevlett.121.136801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Indexed: 06/08/2023]
Abstract
We report the experimental observation of sublattice-resolved resonant scattering in bilayer graphene by performing simultaneous cryogenic atomic hydrogen doping and electron transport measurements in an ultrahigh vacuum. This allows us to monitor the hydrogen adsorption on the different sublattices of bilayer graphene without atomic-scale microscopy. Specifically, we detect two distinct resonant scattering peaks in the gate-dependent resistance, which evolve as a function of the atomic hydrogen dosage. Theoretical calculations show that one of the peaks originates from resonant scattering by hydrogen adatoms on the α sublattice (dimer site) while the other originates from hydrogen adatoms on the β sublattice (nondimer site), thereby enabling a method for characterizing the relative sublattice occupancy via transport measurements. Utilizing this new capability, we investigate the adsorption and thermal desorption of hydrogen adatoms via controlled annealing and conclude that hydrogen adsorption on the β sublattice is energetically favored. Through site-selective desorption from the α sublattice, we realize hydrogen doping with adatoms primarily on a single sublattice, which is highly desired for generating ferromagnetism.
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Affiliation(s)
- Jyoti Katoch
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
- Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Tiancong Zhu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Denis Kochan
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Simranjeet Singh
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
- Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Jaroslav Fabian
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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12
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Xu J, Zhu T, Luo YK, Lu YM, Kawakami RK. Strong and Tunable Spin-Lifetime Anisotropy in Dual-Gated Bilayer Graphene. Phys Rev Lett 2018; 121:127703. [PMID: 30296144 DOI: 10.1103/physrevlett.121.127703] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Indexed: 06/08/2023]
Abstract
We report the discovery of a strong and tunable spin-lifetime anisotropy with excellent out-of-plane spin lifetimes up to 7.8 ns at 100 K in dual-gated bilayer graphene. Remarkably, this realizes the manipulation of spins in graphene by electrically controlled spin-orbit fields, which is unexpected due to graphene's weak intrinsic spin-orbit coupling (∼12 μeV). We utilize both the in-plane magnetic field Hanle precession and oblique Hanle precession measurements to directly compare the lifetimes of out-of-plane vs in-plane spins. We find that near the charge neutrality point, the application of a perpendicular electric field opens a band gap and generates an out-of-plane spin-orbit field that stabilizes out-of-plane spins against spin relaxation, leading to a large spin-lifetime anisotropy (defined as the ratio between out-of-plane and in-plane spin lifetime) up to ∼12 at 100 K. This intriguing behavior occurs because of the unique spin-valley coupled band structure of bilayer graphene. Our results demonstrate the potential for highly tunable spintronic devices based on dual-gated 2D materials.
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Affiliation(s)
- Jinsong Xu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Tiancong Zhu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Yunqiu Kelly Luo
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Yuan-Ming Lu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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13
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Xu J, Singh S, Katoch J, Wu G, Zhu T, Žutić I, Kawakami RK. Spin inversion in graphene spin valves by gate-tunable magnetic proximity effect at one-dimensional contacts. Nat Commun 2018; 9:2869. [PMID: 30030444 PMCID: PMC6054683 DOI: 10.1038/s41467-018-05358-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Accepted: 06/11/2018] [Indexed: 11/08/2022] Open
Abstract
Graphene has remarkable opportunities for spintronics due to its high mobility and long spin diffusion length, especially when encapsulated in hexagonal boron nitride (h-BN). Here, we demonstrate gate-tunable spin transport in such encapsulated graphene-based spin valves with one-dimensional (1D) ferromagnetic edge contacts. An electrostatic backgate tunes the Fermi level of graphene to probe different energy levels of the spin-polarized density of states (DOS) of the 1D ferromagnetic contact, which interact through a magnetic proximity effect (MPE) that induces ferromagnetism in graphene. In contrast to conventional spin valves, where switching between high- and low-resistance configuration requires magnetization reversal by an applied magnetic field or a high-density spin-polarized current, we provide an alternative path with the gate-controlled spin inversion in graphene.
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Affiliation(s)
- Jinsong Xu
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
| | - Simranjeet Singh
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
| | - Jyoti Katoch
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
| | - Guanzhong Wu
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
| | - Tiancong Zhu
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
| | - Igor Žutić
- Department of Physics, University at Buffalo, State University of New York, Buffalo, New York, 14260, USA
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, OH, 43210, USA.
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14
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O'Hara DJ, Zhu T, Trout AH, Ahmed AS, Luo YK, Lee CH, Brenner MR, Rajan S, Gupta JA, McComb DW, Kawakami RK. Room Temperature Intrinsic Ferromagnetism in Epitaxial Manganese Selenide Films in the Monolayer Limit. Nano Lett 2018; 18:3125-3131. [PMID: 29608316 DOI: 10.1021/acs.nanolett.8b00683] [Citation(s) in RCA: 182] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Monolayer van der Waals (vdW) magnets provide an exciting opportunity for exploring two-dimensional (2D) magnetism for scientific and technological advances, but the intrinsic ferromagnetism has only been observed at low temperatures. Here, we report the observation of room temperature ferromagnetism in manganese selenide (MnSe x) films grown by molecular beam epitaxy (MBE). Magnetic and structural characterization provides strong evidence that, in the monolayer limit, the ferromagnetism originates from a vdW manganese diselenide (MnSe2) monolayer, while for thicker films it could originate from a combination of vdW MnSe2 and/or interfacial magnetism of α-MnSe(111). Magnetization measurements of monolayer MnSe x films on GaSe and SnSe2 epilayers show ferromagnetic ordering with a large saturation magnetization of ∼4 Bohr magnetons per Mn, which is consistent with the density functional theory calculations predicting ferromagnetism in monolayer 1T-MnSe2. Growing MnSe x films on GaSe up to a high thickness (∼40 nm) produces α-MnSe(111) and an enhanced magnetic moment (∼2×) compared to the monolayer MnSe x samples. Detailed structural characterization by scanning transmission electron microscopy (STEM), scanning tunneling microscopy (STM), and reflection high energy electron diffraction (RHEED) reveals an abrupt and clean interface between GaSe(0001) and α-MnSe(111). In particular, the structure measured by STEM is consistent with the presence of a MnSe2 monolayer at the interface. These results hold promise for potential applications in energy efficient information storage and processing.
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Affiliation(s)
- Dante J O'Hara
- Materials Science and Engineering , University of California , Riverside , California 92521 , United States
| | - Tiancong Zhu
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Amanda H Trout
- Center for Electron Microscopy and Analysis , The Ohio State University , Columbus , Ohio 43212 , United States
- Department of Materials Science and Engineering , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Adam S Ahmed
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Yunqiu Kelly Luo
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Choong Hee Lee
- Department of Electrical and Computer Engineering , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Mark R Brenner
- Department of Electrical and Computer Engineering , The Ohio State University , Columbus , Ohio 43210 , United States
- Semiconductor Epitaxy and Analysis Laboratory , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Siddharth Rajan
- Department of Materials Science and Engineering , The Ohio State University , Columbus , Ohio 43210 , United States
- Department of Electrical and Computer Engineering , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Jay A Gupta
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
| | - David W McComb
- Center for Electron Microscopy and Analysis , The Ohio State University , Columbus , Ohio 43212 , United States
- Department of Materials Science and Engineering , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Roland K Kawakami
- Materials Science and Engineering , University of California , Riverside , California 92521 , United States
- Department of Physics , The Ohio State University , Columbus , Ohio 43210 , United States
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15
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Singh S, Katoch J, Zhu T, Wu RJ, Ahmed AS, Amamou W, Wang D, Mkhoyan KA, Kawakami RK. Strontium Oxide Tunnel Barriers for High Quality Spin Transport and Large Spin Accumulation in Graphene. Nano Lett 2017; 17:7578-7585. [PMID: 29129075 DOI: 10.1021/acs.nanolett.7b03543] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The quality of the tunnel barrier at the ferromagnet/graphene interface plays a pivotal role in graphene spin valves by circumventing the impedance mismatch problem, decreasing interfacial spin dephasing mechanisms and decreasing spin absorption back into the ferromagnet. It is thus crucial to integrate superior tunnel barriers to enhance spin transport and spin accumulation in graphene. Here, we employ a novel tunnel barrier, strontium oxide (SrO), onto graphene to realize high quality spin transport as evidenced by room-temperature spin relaxation times exceeding a nanosecond in graphene on silicon dioxide substrates. Furthermore, the smooth and pinhole-free SrO tunnel barrier grown by molecular beam epitaxy (MBE), which can withstand large charge injection current densities, allows us to experimentally realize large spin accumulation in graphene at room temperature. This work puts graphene on the path to achieve efficient manipulation of nanomagnet magnetization using spin currents in graphene for logic and memory applications.
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Affiliation(s)
- Simranjeet Singh
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Jyoti Katoch
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Tiancong Zhu
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Ryan J Wu
- Department of Chemical Engineering and Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Adam S Ahmed
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Walid Amamou
- Program of Materials Science and Engineering, University of California , Riverside, California 92521, United States
| | - Dongying Wang
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - K Andre Mkhoyan
- Department of Chemical Engineering and Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Roland K Kawakami
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
- Program of Materials Science and Engineering, University of California , Riverside, California 92521, United States
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16
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Luo YK, Xu J, Zhu T, Wu G, McCormick EJ, Zhan W, Neupane MR, Kawakami RK. Opto-Valleytronic Spin Injection in Monolayer MoS 2/Few-Layer Graphene Hybrid Spin Valves. Nano Lett 2017; 17:3877-3883. [PMID: 28534400 DOI: 10.1021/acs.nanolett.7b01393] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Two-dimensional (2D) materials provide a unique platform for spintronics and valleytronics due to the ability to combine vastly different functionalities into one vertically stacked heterostructure, where the strengths of each of the constituent materials can compensate for the weaknesses of the others. Graphene has been demonstrated to be an exceptional material for spin transport at room temperature; however, it lacks a coupling of the spin and optical degrees of freedom. In contrast, spin/valley polarization can be efficiently generated in monolayer transition metal dichalcogenides (TMD) such as MoS2 via absorption of circularly polarized photons, but lateral spin or valley transport has not been realized at room temperature. In this Letter, we fabricate monolayer MoS2/few-layer graphene hybrid spin valves and demonstrate, for the first time, the opto-valleytronic spin injection across a TMD/graphene interface. We observe that the magnitude and direction of spin polarization is controlled by both helicity and photon energy. In addition, Hanle spin precession measurements confirm optical spin injection, spin transport, and electrical detection up to room temperature. Finally, analysis by a one-dimensional drift-diffusion model quantifies the optically injected spin current and the spin transport parameters. Our results demonstrate a 2D spintronic/valleytronic system that achieves optical spin injection and lateral spin transport at room temperature in a single device, which paves the way for multifunctional 2D spintronic devices for memory and logic applications.
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Affiliation(s)
- Yunqiu Kelly Luo
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Jinsong Xu
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Tiancong Zhu
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Guanzhong Wu
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Elizabeth J McCormick
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Wenbo Zhan
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Mahesh R Neupane
- Sensors and Electron Devices Directorate, U.S. Army Research Laboratory , Adelphi, Maryland 20783, United States
| | - Roland K Kawakami
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
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17
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Singh S, Katoch J, Zhu T, Meng KY, Liu T, Brangham JT, Yang F, Flatté ME, Kawakami RK. Strong Modulation of Spin Currents in Bilayer Graphene by Static and Fluctuating Proximity Exchange Fields. Phys Rev Lett 2017; 118:187201. [PMID: 28524685 DOI: 10.1103/physrevlett.118.187201] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Indexed: 06/07/2023]
Abstract
Two-dimensional materials provide a unique platform to explore the full potential of magnetic proximity-driven phenomena, which can be further used for applications in next-generation spintronic devices. Of particular interest is to understand and control spin currents in graphene by the magnetic exchange field of a nearby ferromagnetic material in graphene-ferromagnetic-insulator (FMI) heterostructures. Here, we present the experimental study showing the strong modulation of spin currents in graphene layers by controlling the direction of the exchange field due to FMI magnetization. Owing to clean interfaces, a strong magnetic exchange coupling leads to the experimental observation of complete spin modulation at low externally applied magnetic fields in short graphene channels. Additionally, we discover that the graphene spin current can be fully dephased by randomly fluctuating exchange fields. This is manifested as an unusually strong temperature dependence of the nonlocal spin signals in graphene, which is due to spin relaxation by thermally induced transverse fluctuations of the FMI magnetization.
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Affiliation(s)
- Simranjeet Singh
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Jyoti Katoch
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Tiancong Zhu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Keng-Yuan Meng
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Tianyu Liu
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Jack T Brangham
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Fengyuan Yang
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Michael E Flatté
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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18
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Ulstrup S, Katoch J, Koch RJ, Schwarz D, Singh S, McCreary KM, Yoo HK, Xu J, Jonker BT, Kawakami RK, Bostwick A, Rotenberg E, Jozwiak C. Spatially Resolved Electronic Properties of Single-Layer WS 2 on Transition Metal Oxides. ACS Nano 2016; 10:10058-10067. [PMID: 27768848 DOI: 10.1021/acsnano.6b04914] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
There is a substantial interest in the heterostructures of semiconducting transition metal dichalcogenides (TMDCs) among each other or with arbitrary materials, through which the control of the chemical, structural, electronic, spintronic, and optical properties can lead to a change in device paradigms. A critical need is to understand the interface between TMDCs and insulating substrates, for example, high-κ dielectrics, which can strongly impact the electronic properties such as the optical gap. Here, we show that the chemical and electronic properties of the single-layer (SL) TMDC, WS2, can be transferred onto high-κ transition metal oxide substrates TiO2 and SrTiO3. The resulting samples are much more suitable for measuring their electronic and chemical structures with angle-resolved photoemission than their native-grown SiO2 substrates. We probe the WS2 on the micron scale across 100 μm flakes and find that the occupied electronic structure is exactly as predicted for free-standing SL WS2 with a strong spin-orbit splitting of 420 meV and a direct band gap at the valence band maximum. Our results suggest that TMDCs can be combined with arbitrary multifunctional oxides, which may introduce alternative means of controlling the optoelectronic properties of such materials.
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Affiliation(s)
- Søren Ulstrup
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Jyoti Katoch
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Roland J Koch
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Daniel Schwarz
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Simranjeet Singh
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | | | - Hyang Keun Yoo
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Jinsong Xu
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Berend T Jonker
- Naval Research Laboratory , Washington, D.C. 20375, United States
| | - Roland K Kawakami
- Department of Physics, The Ohio State University , Columbus, Ohio 43210, United States
| | - Aaron Bostwick
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Eli Rotenberg
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Chris Jozwiak
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
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19
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Arguilla MQ, Katoch J, Krymowski K, Cultrara ND, Xu J, Xi X, Hanks A, Jiang S, Ross RD, Koch RJ, Ulstrup S, Bostwick A, Jozwiak C, McComb DW, Rotenberg E, Shan J, Windl W, Kawakami RK, Goldberger JE. NaSn 2As 2: An Exfoliatable Layered van der Waals Zintl Phase. ACS Nano 2016; 10:9500-9508. [PMID: 27700035 DOI: 10.1021/acsnano.6b04609] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The discovery of new families of exfoliatable 2D crystals that have diverse sets of electronic, optical, and spin-orbit coupling properties enables the realization of unique physical phenomena in these few-atom-thick building blocks and in proximity to other materials. Herein, using NaSn2As2 as a model system, we demonstrate that layered Zintl phases having the stoichiometry ATt2Pn2 (A = group 1 or 2 element, Tt = group 14 tetrel element, and Pn = group 15 pnictogen element) and feature networks separated by van der Waals gaps can be readily exfoliated with both mechanical and liquid-phase methods. We identified the symmetries of the Raman-active modes of the bulk crystals via polarized Raman spectroscopy. The bulk and mechanically exfoliated NaSn2As2 samples are resistant toward oxidation, with only the top surface oxidizing in ambient conditions over a couple of days, while the liquid-exfoliated samples oxidize much more quickly in ambient conditions. Employing angle-resolved photoemission spectroscopy, density functional theory, and transport on bulk and exfoliated samples, we show that NaSn2As2 is a highly conducting 2D semimetal, with resistivities on the order of 10-6 Ω·m. Due to peculiarities in the band structure, the dominating p-type carriers at low temperature are nearly compensated by the opening of n-type conduction channels as temperature increases. This work further expands the family of exfoliatable 2D materials to layered van der Waals Zintl phases, opening up opportunities in electronics and spintronics.
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Affiliation(s)
| | | | | | | | | | - Xiaoxiang Xi
- Department of Physics, The Pennsylvania State University , University Park, Pennsylvania 16802-6300, United States
| | | | | | | | - Roland J Koch
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Søren Ulstrup
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Aaron Bostwick
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Chris Jozwiak
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | | | - Eli Rotenberg
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Jie Shan
- Department of Physics, The Pennsylvania State University , University Park, Pennsylvania 16802-6300, United States
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20
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Ou YS, Chiu YH, Harmon NJ, Odenthal P, Sheffield M, Chilcote M, Kawakami RK, Flatté ME, Johnston-Halperin E. Exchange-Driven Spin Relaxation in Ferromagnet-Oxide-Semiconductor Heterostructures. Phys Rev Lett 2016; 116:107201. [PMID: 27015506 DOI: 10.1103/physrevlett.116.107201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Indexed: 06/05/2023]
Abstract
We demonstrate that electron spin relaxation in GaAs in the proximity of a Fe/MgO layer is dominated by interaction with an exchange-driven hyperfine field at temperatures below 60 K. Temperature-dependent spin-resolved optical pump-probe spectroscopy reveals a strong correlation of the electron spin relaxation with carrier freeze-out, in quantitative agreement with a theoretical interpretation that at low temperatures the free-carrier spin lifetime is dominated by inhomogeneity in the local hyperfine field due to carrier localization. As the regime of large nuclear inhomogeneity is accessible in these heterostructures for magnetic fields <3 kG, inferences from this result resolve a long-standing and contentious dispute concerning the origin of spin relaxation in GaAs at low temperature when a magnetic field is present. Further, this improved fundamental understanding clarifies the importance of future experiments probing the time-dependent exchange interaction at a ferromagnet-semiconductor interface and its consequences for spin dissipation and transport during spin pumping.
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Affiliation(s)
- Yu-Sheng Ou
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
| | - Yi-Hsin Chiu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
| | - N J Harmon
- Department of Physics and Astronomy, The University of Iowa, Iowa City, Iowa 52242-1479, USA
| | - Patrick Odenthal
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - Matthew Sheffield
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
| | - Michael Chilcote
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
| | - R K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - M E Flatté
- Department of Physics and Astronomy, The University of Iowa, Iowa City, Iowa 52242-1479, USA
| | - E Johnston-Halperin
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
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21
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Pu Y, Odenthal PM, Adur R, Beardsley J, Swartz AG, Pelekhov DV, Flatté ME, Kawakami RK, Pelz J, Hammel PC, Johnston-Halperin E. Ferromagnetic Resonance Spin Pumping and Electrical Spin Injection in Silicon-Based Metal-Oxide-Semiconductor Heterostructures. Phys Rev Lett 2015; 115:246602. [PMID: 26705647 DOI: 10.1103/physrevlett.115.246602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Indexed: 06/05/2023]
Abstract
We present the measurement of ferromagnetic resonance (FMR-)driven spin pumping and three-terminal electrical spin injection within the same silicon-based device. Both effects manifest in a dc spin accumulation voltage V_{s} that is suppressed as an applied field is rotated to the out-of-plane direction, i.e., the oblique Hanle geometry. Comparison of V_{s} between these two spin injection mechanisms reveals an anomalously strong suppression of FMR-driven spin pumping with increasing out-of-plane field H_{app}^{z}. We propose that the presence of the large ac component to the spin current generated by the spin pumping approach, expected to exceed the dc value by 2 orders of magnitude, is the origin of this discrepancy through its influence on the spin dynamics at the oxide-silicon interface. This convolution, wherein the dynamics of both the injector and the interface play a significant role in the spin accumulation, represents a new regime for spin injection that is not well described by existing models of either FMR-driven spin pumping or electrical spin injection.
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Affiliation(s)
- Y Pu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - P M Odenthal
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - R Adur
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - J Beardsley
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - A G Swartz
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - D V Pelekhov
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - M E Flatté
- Departent of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - R K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - J Pelz
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - P C Hammel
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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22
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Abstract
The isolation of graphene has triggered an avalanche of studies into the spin-dependent physical properties of this material and of graphene-based spintronic devices. Here, we review the experimental and theoretical state-of-art concerning spin injection and transport, defect-induced magnetic moments, spin-orbit coupling and spin relaxation in graphene. Future research in graphene spintronics will need to address the development of applications such as spin transistors and spin logic devices, as well as exotic physical properties including topological states and proximity-induced phenomena in graphene and other two-dimensional materials.
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Affiliation(s)
- Wei Han
- 1] International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China [2] Collaborative Innovation Center of Quantum Matter, Beijing 100871, China [3] IBM Almaden Research Center, San Jose, California 95120, USA
| | - Roland K Kawakami
- 1] Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA [2] Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - Martin Gmitra
- Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - Jaroslav Fabian
- Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
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23
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Abstract
Junctions comprised of ferromagnets and nonmagnetic materials are one of the key building blocks in spintronics. With the recent breakthroughs of spin injection in ferromagnet/graphene junctions it is possible to consider spin-based applications that are not limited to magnetoresistive effects. However, for critical studies of such structures it is crucial to establish accurate predictive methods that would yield atomically resolved information on interfacial properties. By focusing on Co(0001)/graphene junctions and their electronic structure, we illustrate the inequivalence of different spin polarizations. We show atomically resolved spin polarization maps as a useful approach to assess the relevance of Co(0001)/graphene for different spintronics applications.
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Affiliation(s)
- G M Sipahi
- Department of Physics, University at Buffalo, State University of New York, Buffalo, NY 14260, USA
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24
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Chen JR, Odenthal PM, Swartz AG, Floyd GC, Wen H, Luo KY, Kawakami RK. Control of Schottky barriers in single layer MoS2 transistors with ferromagnetic contacts. Nano Lett 2013; 13:3106-3110. [PMID: 23746085 DOI: 10.1021/nl4010157] [Citation(s) in RCA: 181] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
MoS2 and related metal dichalcogenides (MoSe2, WS2, WSe2) are layered two-dimensional materials that are promising for nanoelectronics and spintronics. For instance, large spin-orbit coupling and spin splitting in the valence band of single layer (SL) MoS2 could lead to enhanced spin lifetimes and large spin Hall angles. Understanding the nature of the contacts is a critical first step for realizing spin injection and spin transport in MoS2. Here, we have investigated Co contacts to SL MoS2 and find that the Schottky barrier height can be significantly decreased with the addition of a thin oxide barrier (MgO). Further, we show that the barrier height can be reduced to zero by tuning the carrier density with back gate. Therefore, the MgO could simultaneously provide a tunnel barrier to alleviate conductance mismatch while minimizing carrier depletion near the contacts. Such control over the barrier height should allow for careful engineering of the contacts to realize spin injection in these materials.
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Affiliation(s)
- Jen-Ru Chen
- Department of Physics and Astronomy, University of California , Riverside, California, United States
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25
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Abstract
We have demonstrated the deposition of EuO films on graphene by reactive molecular beam epitaxy in a special adsorption-controlled and oxygen-limited regime, which is a critical advance toward the realization of the exchange proximity interaction (EPI). It has been predicted that when the ferromagnetic insulator (FMI) EuO is brought into contact with graphene, an overlap of electronic wave functions at the FMI/graphene interface can induce a large spin splitting inside the graphene. Experimental realization of this effect could lead to new routes for spin manipulation, which is a necessary requirement for a functional spin transistor. Furthermore, EPI could lead to novel spintronic behavior such as controllable magnetoresistance, gate tunable exchange bias, and quantized anomalous Hall effect. However, experimentally, EuO has not yet been integrated onto graphene. Here we report the successful growth of high-quality crystalline EuO on highly oriented pyrolytic graphite and single-layer graphene. The epitaxial EuO layers have (001) orientation and do not induce an observable D peak (defect) in the Raman spectra. Magneto-optic measurements indicate ferromagnetism with a Curie temperature of 69 K, which is the value for bulk EuO. Transport measurements on exfoliated graphene before and after EuO deposition indicate only a slight decrease in mobility.
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Affiliation(s)
- Adrian G Swartz
- Department of Physics and Astronomy, University of California, Riverside, California 92521, United States
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McCreary KM, Swartz AG, Han W, Fabian J, Kawakami RK. Magnetic moment formation in graphene detected by scattering of pure spin currents. Phys Rev Lett 2012; 109:186604. [PMID: 23215308 DOI: 10.1103/physrevlett.109.186604] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2012] [Indexed: 05/22/2023]
Abstract
Hydrogen adatoms are shown to generate magnetic moments inside single layer graphene. Spin transport measurements on graphene spin valves exhibit a dip in the nonlocal spin signal as a function of the applied magnetic field, which is due to scattering (relaxation) of pure spin currents by exchange coupling to the magnetic moments. Furthermore, Hanle spin precession measurements indicate the presence of an exchange field generated by the magnetic moments. The entire experiment including spin transport is performed in an ultrahigh vacuum chamber, and the characteristic signatures of magnetic moment formation appear only after hydrogen adatoms are introduced. Lattice vacancies also demonstrate similar behavior indicating that the magnetic moment formation originates from p(z)-orbital defects.
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Affiliation(s)
- Kathleen M McCreary
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
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Han W, Chen JR, Wang D, McCreary KM, Wen H, Swartz AG, Shi J, Kawakami RK. Spin relaxation in single-layer graphene with tunable mobility. Nano Lett 2012; 12:3443-3447. [PMID: 22725628 DOI: 10.1021/nl301567n] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Graphene is an attractive material for spintronics due to theoretical predictions of long spin lifetimes arising from low spin-orbit and hyperfine couplings. In experiments, however, spin lifetimes in single-layer graphene (SLG) measured via Hanle effects are much shorter than expected theoretically. Thus, the origin of spin relaxation in SLG is a major issue for graphene spintronics. Despite extensive theoretical and experimental work addressing this question, there is still little clarity on the microscopic origin of spin relaxation. By using organic ligand-bound nanoparticles as charge reservoirs to tune the mobility between 2700 and 12 000 cm(2)/(V s), we successfully isolate the effect of charged impurity scattering on spin relaxation in SLG. Our results demonstrate that, while charged impurities can greatly affect mobility, the spin lifetimes are not affected by charged impurity scattering.
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Affiliation(s)
- Wei Han
- Department of Physics and Astronomy, University of California, Riverside, California 92521, United States
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28
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Abstract
We investigate spin relaxation in graphene spin valves and observe strongly contrasting behavior for single-layer graphene (SLG) and bilayer graphene (BLG). In SLG, the spin lifetime (τ(s)) varies linearly with the momentum scattering time (τ(p)) as carrier concentration is varied, indicating the dominance of Elliot-Yafet (EY) spin relaxation at low temperatures. In BLG, τ(s) and τ(p) exhibit an inverse dependence, which indicates the dominance of Dyakonov-Perel spin relaxation at low temperatures. The different behavior is due to enhanced screening and/or reduced surface sensitivity of BLG, which greatly reduces the impurity-induced EY spin relaxation.
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Affiliation(s)
- Wei Han
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
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Han W, Pi K, McCreary KM, Li Y, Wong JJI, Swartz AG, Kawakami RK. Tunneling spin injection into single layer graphene. Phys Rev Lett 2010; 105:167202. [PMID: 21231003 DOI: 10.1103/physrevlett.105.167202] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2010] [Indexed: 05/22/2023]
Abstract
We achieve tunneling spin injection from Co into single layer graphene (SLG) using TiO₂ seeded MgO barriers. A nonlocal magnetoresistance (ΔR(NL)) of 130 Ω is observed at room temperature, which is the largest value observed in any material. Investigating ΔR(NL) vs SLG conductivity from the transparent to the tunneling contact regimes demonstrates the contrasting behaviors predicted by the drift-diffusion theory of spin transport. Furthermore, tunnel barriers reduce the contact-induced spin relaxation and are therefore important for future investigations of spin relaxation in graphene.
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Affiliation(s)
- Wei Han
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
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30
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Li Y, Han W, Swartz AG, Pi K, Wong JJI, Mack S, Awschalom DD, Kawakami RK. Oscillatory spin polarization and magneto-optical Kerr effect in Fe₃O₄ thin films on GaAs(001). Phys Rev Lett 2010; 105:167203. [PMID: 21231004 DOI: 10.1103/physrevlett.105.167203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2010] [Indexed: 05/30/2023]
Abstract
The spin dependent properties of epitaxial Fe₃O₄ thin films on GaAs(001) are studied by the ferromagnetic proximity polarization (FPP) effect and magneto-optical Kerr effect (MOKE). Both FPP and MOKE show oscillations with respect to Fe₃O₄ film thickness, and the oscillations are large enough to induce repeated sign reversals. We attribute the oscillatory behavior to spin-polarized quantum well states forming in the Fe₃O₄ film. Quantum confinement of the t(2g) states near the Fermi level provides an explanation for the similar thickness dependences of the FPP and MOKE oscillations.
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Affiliation(s)
- Yan Li
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
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31
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Xiu F, Wang Y, Kim J, Upadhyaya P, Zhou Y, Kou X, Han W, Kawakami RK, Zou J, Wang KL. Room-temperature electric-field controlled ferromagnetism in Mn0.05Ge0.95 quantum dots. ACS Nano 2010; 4:4948-4954. [PMID: 20666361 DOI: 10.1021/nn101516t] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Room-temperature control of ferromagnetism by electric fields in magnetic semiconductors has been actively pursued as one of important approaches to realize practical spintronic and nonvolatile logic devices. While Mn-doped III-V semiconductors were considered as potential candidates for achieving this controllability, the search for an ideal material with high Curie temperature (T(c) > 300 K) and controllable ferromagnetism at room temperature has continued for nearly a decade. Recently, Mn(0.05)Ge(0.95) quantum dots (QDs) were demonstrated to have a T(c) above 300 K. However, the field control of ferromagnetism based on hole-mediated effect remained at low temperatures and thus prohibited spintronic devices operable at ambient environment. Here, we report a successful demonstration of electric-field control of ferromagnetism in the Mn(0.05)Ge(0.95) quantum dots up to 300 K. We show that, by using quantum structure, high-quality material can be obtained and effective hole mediation due to quantum confinement effect can be achieved. Upon the application of gate bias to a metal-oxide-semiconductor (MOS) capacitor, the ferromagnetism of the channel layer, that is, the Mn(0.05)Ge(0.95) quantum dots, was manipulated through the change of hole concentration. Our results are fundamentally and technologically important toward the realization of room-temperature spin field-effect transistors and nonvolatile spin logic devices.
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Affiliation(s)
- Faxian Xiu
- Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA.
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32
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Pi K, Han W, McCreary KM, Swartz AG, Li Y, Kawakami RK. Manipulation of spin transport in graphene by surface chemical doping. Phys Rev Lett 2010; 104:187201. [PMID: 20482203 DOI: 10.1103/physrevlett.104.187201] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2009] [Indexed: 05/29/2023]
Abstract
The effects of surface chemical doping on spin transport in graphene are investigated by performing nonlocal measurements in ultrahigh vacuum while depositing gold adsorbates. We demonstrate manipulation of the gate-dependent nonlocal spin signal as a function of gold coverage. We discover that charged impurity scattering is not the dominant mechanism for spin relaxation in graphene, despite its importance for momentum scattering. Finally, unexpected enhancements of the spin lifetime illustrate the complex nature of spin relaxation in graphene.
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Affiliation(s)
- K Pi
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
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33
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Han W, Wang WH, Pi K, McCreary KM, Bao W, Li Y, Miao F, Lau CN, Kawakami RK. Electron-hole asymmetry of spin injection and transport in single-layer graphene. Phys Rev Lett 2009; 102:137205. [PMID: 19392401 DOI: 10.1103/physrevlett.102.137205] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2008] [Indexed: 05/27/2023]
Abstract
Spin-dependent properties of single-layer graphene (SLG) have been studied by nonlocal spin valve measurements at room temperature. Gate voltage dependence shows that the nonlocal magnetoresistance (MR) is proportional to the conductivity of the SLG, which is the predicted behavior for transparent ferromagnetic-nonmagnetic contacts. While the electron and hole bands in SLG are symmetric, gate voltage and bias dependence of the nonlocal MR reveal an electron-hole asymmetry in which the nonlocal MR is roughly independent of bias for electrons, but varies significantly with bias for holes.
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Affiliation(s)
- Wei Han
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
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34
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Li Y, Chye Y, Chiang YF, Pi K, Wang WH, Stephens JM, Mack S, Awschalom DD, Kawakami RK. Inversion of ferromagnetic proximity polarization by MgO interlayers. Phys Rev Lett 2008; 100:237205. [PMID: 18643542 DOI: 10.1103/physrevlett.100.237205] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2008] [Indexed: 05/26/2023]
Abstract
We investigate the spin-dependent reflection properties in Fe/MgO/GaAs heterostructures by optical pump-probe measurement of the ferromagnetic proximity polarization (FPP). As a function of MgO thickness, the FPP is initially enhanced (<2.0 A) and then exhibits an unexpected sign reversal at approximately 5.0 A. The identification of two competing thresholds in the intensity dependence of FPP and the observation of FPP sign reversal in Fe/Mg/GaAs suggest that the inversion of FPP is related to an interfacial bonding effect.
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Affiliation(s)
- Yan Li
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
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35
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Burch KS, Shrekenhamer DB, Singley EJ, Stephens J, Sheu BL, Kawakami RK, Schiffer P, Samarth N, Awschalom DD, Basov DN. Impurity band conduction in a high temperature ferromagnetic semiconductor. Phys Rev Lett 2006; 97:087208. [PMID: 17026333 DOI: 10.1103/physrevlett.97.087208] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2006] [Indexed: 05/12/2023]
Abstract
The band structure of a prototypical dilute magnetic semiconductor (DMS), Ga1-xMnxAs, is studied across the phase diagram via infrared and optical spectroscopy. We prove that the Fermi energy (EF) resides in a Mn-induced impurity band (IB). Specifically the changes in the frequency dependent optical conductivity [sigma1(omega)] with carrier density are only consistent with EF lying in an IB. Furthermore, the large effective mass (m*) of the carriers inferred from our analysis of sigma1(omega) supports this conclusion. Our findings demonstrate that the metal to insulator transition in this DMS is qualitatively different from other III-V semiconductors doped with nonmagnetic impurities. We also provide insights into the anomalous transport properties of Ga1-xMnxAs.
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Affiliation(s)
- K S Burch
- Department of Physics, University of California, San Diego, California 92093-0319, USA.
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36
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Tang HX, Masmanidis S, Kawakami RK, Awschalom DD, Roukes ML. Negative intrinsic resistivity of an individual domain wall in epitaxial (Ga,Mn)As microdevices. Nature 2004; 431:52-6. [PMID: 15343329 DOI: 10.1038/nature02809] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2004] [Accepted: 07/02/2004] [Indexed: 11/09/2022]
Abstract
Magnetic domains, and the boundaries that separate them (domain walls, DWs), play a central role in the science of magnetism. Understanding and controlling domains is important for many technological applications in spintronics, and may lead to new devices. Although theoretical efforts have elucidated several mechanisms underlying the resistance of a single DW, various experiments report conflicting results, even for the overall sign of the DW resistance. The question of whether an individual DW gives rise to an increase or decrease of the resistance therefore remains open. Here we report an approach to DW studies in a class of ferromagnetic semiconductors (as opposed to metals) that offer promise for spintronics. These experiments involve microdevices patterned from monocrystalline (Ga,Mn)As epitaxial layers. The giant planar Hall effect that we previously observed in this material enables direct, real-time observation of the propagation of an individual magnetic DW along multiprobe devices. We apply steady and pulsed magnetic fields, to trap and carefully position an individual DW within each separate device studied. This protocol reproducibly enables high-resolution magnetoresistance measurements across an individual wall. We consistently observe negative intrinsic DW resistance that scales with channel width. This appears to originate from sizeable quantum corrections to the magnetoresistance.
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Affiliation(s)
- H X Tang
- Condensed Matter Physics 114-36, California Institute of Technology, Pasadena, California 91125, USA
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Tang HX, Kawakami RK, Awschalom DD, Roukes ML. Giant planar Hall effect in epitaxial (Ga,Mn)as devices. Phys Rev Lett 2003; 90:107201. [PMID: 12689027 DOI: 10.1103/physrevlett.90.107201] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2002] [Indexed: 05/24/2023]
Abstract
Large Hall resistance jumps are observed in microdevices patterned from epitaxial (Ga,Mn)As layers when subjected to a swept, in-plane magnetic field. This giant planar Hall effect is 4 orders of magnitude greater than previously observed in metallic ferromagnets. This enables extremely sensitive measurements of the angle-dependent magnetic properties of (Ga,Mn)As. The magnetic anisotropy fields deduced from these measurements are compared with theoretical predictions.
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Affiliation(s)
- H X Tang
- Condensed Matter Physics 114-36, California Institute of Technology, Pasadena, California 91125, USA
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38
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Kawakami RK, Kato Y, Hanson M, Malajovich I, Stephens JM, Johnston-Halperin E, Salis G, Gossard AC, Awschalom DD. Ferromagnetic imprinting of nuclear spins in semiconductors. Science 2001; 294:131-4. [PMID: 11588255 DOI: 10.1126/science.1063186] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We examine how a ferromagnetic layer affects the coherent electron spin dynamics in a neighboring gallium arsenide semiconductor. Ultrafast optical pump-probe measurements reveal that the spin dynamics are unexpectedly dominated by hyperpolarized nuclear spins that align along the ferromagnet's magnetization. We find evidence that photoexcited carriers acquire spin-polarization from the ferromagnet, and dynamically polarize these nuclear spins. The resulting hyperfine fields are as high as 9000 gauss in small external fields (less than 1000 gauss), enabling ferromagnetic control of local electron spin coherence.
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Affiliation(s)
- R K Kawakami
- Department of Physics and, Materials Department, University of California, Santa Barbara, CA 93106, USA
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Sameshima GT, Kawakami RK, Kaminishi RM, Sinclair PM. Predicting soft tissue changes in maxillary impaction surgery: a comparison of two video imaging systems. Angle Orthod 1997; 67:347-54. [PMID: 9347108 DOI: 10.1043/0003-3219(1997)067<0347:pstcim>2.3.co;2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The purpose of this retrospective study was to investigate the accuracy of two video imaging systems, Orthognathic Treatment Planner (OTP) and Prescription Portrait (Portrait), in predicting soft tissue profile changes after maxillary impaction surgery. Computer-generated line drawing predictions were compared with actual postsurgical profiles. Neither program was very accurate with vertical measures and lower lip contour. Portrait was more accurate at pronasale, inferior labial sulcus, and pogonion in the y-axis direction (P < 0.05). Video image predictions produced from the presurgical photographs were rated by orthodontists, surgeons, and lay people, who compared the predictions with the actual postsurgical photographs using a visual analog scale. Portrait's prediction images were scored higher than OTP's for five of eight areas. Orthodontists were most critical of the lips and the overall appearance. Lay people were most critical of the chin and submental areas.
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Affiliation(s)
- G T Sameshima
- Dept. of Orthodontics, USC School of Dentistry, Los Angeles 90089-0641, USA.
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Kawakami RK, Escorcia-Aparicio EJ, Qiu ZQ. Symmetry-Induced Magnetic Anisotropy in Fe Films Grown on Stepped Ag(001). Phys Rev Lett 1996; 77:2570-2573. [PMID: 10061987 DOI: 10.1103/physrevlett.77.2570] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Escorcia-Aparicio EJ, Kawakami RK, Qiu ZQ. fcc Fe films grown on a ferromagnetic fcc Co(100) substrate. Phys Rev B Condens Matter 1996; 54:4155-4158. [PMID: 9986318 DOI: 10.1103/physrevb.54.4155] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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