1
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Hou Y, Nichele F, Chi H, Lodesani A, Wu Y, Ritter MF, Haxell DZ, Davydova M, Ilić S, Glezakou-Elbert O, Varambally A, Bergeret FS, Kamra A, Fu L, Lee PA, Moodera JS. Ubiquitous Superconducting Diode Effect in Superconductor Thin Films. Phys Rev Lett 2023; 131:027001. [PMID: 37505965 DOI: 10.1103/physrevlett.131.027001] [Citation(s) in RCA: 3] [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: 11/01/2022] [Accepted: 05/09/2023] [Indexed: 07/30/2023]
Abstract
The macroscopic coherence in superconductors supports dissipationless supercurrents that could play a central role in emerging quantum technologies. Accomplishing unequal supercurrents in the forward and backward directions would enable unprecedented functionalities. This nonreciprocity of critical supercurrents is called the superconducting (SC) diode effect. We demonstrate the strong SC diode effect in conventional SC thin films, such as niobium and vanadium, employing external magnetic fields as small as 1 Oe. Interfacing the SC layer with a ferromagnetic semiconductor EuS, we further accomplish the nonvolatile SC diode effect reaching a giant efficiency of 65%. By careful control experiments and theoretical modeling, we demonstrate that the critical supercurrent nonreciprocity in SC thin films could be easily accomplished with asymmetrical vortex edge and surface barriers and the universal Meissner screening current governing the critical currents. Our engineering of the SC diode effect in simple systems opens the door for novel technologies while revealing the ubiquity of the Meissner screening effect induced SC diode effect in superconducting films, and it should be eliminated with great care in the search for exotic superconducting states harboring finite-momentum Cooper pairing.
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Affiliation(s)
- Yasen Hou
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Fabrizio Nichele
- IBM Research Europe - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | - Hang Chi
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- U.S. Army DEVCOM Army Research Laboratory, Adelphi, Maryland 20783, USA
| | - Alessandro Lodesani
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Yingying Wu
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Markus F Ritter
- IBM Research Europe - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | - Daniel Z Haxell
- IBM Research Europe - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | - Margarita Davydova
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Stefan Ilić
- Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Pº Manuel de Lardizabal 5, Donostia-San Sebastián 20018, Spain
| | | | | | - F Sebastian Bergeret
- Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Pº Manuel de Lardizabal 5, Donostia-San Sebastián 20018, Spain
- Donostia International Physics Center (DIPC), Donostia-San Sebastián 20018, Spain
| | - Akashdeep Kamra
- Condensed Matter Physics Center (IFIMAC) and Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Patrick A Lee
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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2
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Chi H, Ou Y, Eldred TB, Gao W, Kwon S, Murray J, Dreyer M, Butera RE, Foucher AC, Ambaye H, Keum J, Greenberg AT, Liu Y, Neupane MR, de Coster GJ, Vail OA, Taylor PJ, Folkes PA, Rong C, Yin G, Lake RK, Ross FM, Lauter V, Heiman D, Moodera JS. Strain-tunable Berry curvature in quasi-two-dimensional chromium telluride. Nat Commun 2023; 14:3222. [PMID: 37270579 DOI: 10.1038/s41467-023-38995-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Accepted: 05/24/2023] [Indexed: 06/05/2023] Open
Abstract
Magnetic transition metal chalcogenides form an emerging platform for exploring spin-orbit driven Berry phase phenomena owing to the nontrivial interplay between topology and magnetism. Here we show that the anomalous Hall effect in pristine Cr2Te3 thin films manifests a unique temperature-dependent sign reversal at nonzero magnetization, resulting from the momentum-space Berry curvature as established by first-principles simulations. The sign change is strain tunable, enabled by the sharp and well-defined substrate/film interface in the quasi-two-dimensional Cr2Te3 epitaxial films, revealed by scanning transmission electron microscopy and depth-sensitive polarized neutron reflectometry. This Berry phase effect further introduces hump-shaped Hall peaks in pristine Cr2Te3 near the coercive field during the magnetization switching process, owing to the presence of strain-modulated magnetic layers/domains. The versatile interface tunability of Berry curvature in Cr2Te3 thin films offers new opportunities for topological electronics.
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Affiliation(s)
- Hang Chi
- Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
- DEVCOM Army Research Laboratory, Adelphi, MD, 20783, USA.
| | - Yunbo Ou
- Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
| | - Tim B Eldred
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Wenpei Gao
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Sohee Kwon
- Department of Electrical and Computer Engineering, University of California, Riverside, CA, 92521, USA
| | - Joseph Murray
- Department of Physics, University of Maryland, College Park, MD, 20742, USA
| | - Michael Dreyer
- Department of Physics, University of Maryland, College Park, MD, 20742, USA
| | - Robert E Butera
- Laboratory for Physical Sciences, College Park, MD, 20740, USA
| | - Alexandre C Foucher
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Haile Ambaye
- Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Jong Keum
- Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
- Center for Nanophase Materials Sciences, Physical Science Directorate, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | | | - Yuhang Liu
- Department of Electrical and Computer Engineering, University of California, Riverside, CA, 92521, USA
| | - Mahesh R Neupane
- DEVCOM Army Research Laboratory, Adelphi, MD, 20783, USA
- Department of Electrical and Computer Engineering, University of California, Riverside, CA, 92521, USA
| | | | - Owen A Vail
- DEVCOM Army Research Laboratory, Adelphi, MD, 20783, USA
| | | | | | - Charles Rong
- DEVCOM Army Research Laboratory, Adelphi, MD, 20783, USA
| | - Gen Yin
- Department of Physics, Georgetown University, Washington, DC, 20057, USA
| | - Roger K Lake
- Department of Electrical and Computer Engineering, University of California, Riverside, CA, 92521, USA
| | - Frances M Ross
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Valeria Lauter
- Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Don Heiman
- Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Department of Physics, Northeastern University, Boston, MA, 02115, USA
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
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3
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Klein J, Song Z, Pingault B, Dirnberger F, Chi H, Curtis JB, Dana R, Bushati R, Quan J, Dekanovsky L, Sofer Z, Alù A, Menon VM, Moodera JS, Lončar M, Narang P, Ross FM. Sensing the Local Magnetic Environment through Optically Active Defects in a Layered Magnetic Semiconductor. ACS Nano 2023; 17:288-299. [PMID: 36537371 DOI: 10.1021/acsnano.2c07655] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Atomic-level defects in van der Waals (vdW) materials are essential building blocks for quantum technologies and quantum sensing applications. The layered magnetic semiconductor CrSBr is an outstanding candidate for exploring optically active defects because of a direct gap, in addition to a rich magnetic phase diagram, including a recently hypothesized defect-induced magnetic order at low temperature. Here, we show optically active defects in CrSBr that are probes of the local magnetic environment. We observe a spectrally narrow (1 meV) defect emission in CrSBr that is correlated with both the bulk magnetic order and an additional low-temperature, defect-induced magnetic order. We elucidate the origin of this magnetic order in the context of local and nonlocal exchange coupling effects. Our work establishes vdW magnets like CrSBr as an exceptional platform to optically study defects that are correlated with the magnetic lattice. We anticipate that controlled defect creation allows for tailor-made complex magnetic textures and phases with direct optical access.
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Affiliation(s)
- Julian Klein
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts02139, United States
| | - Zhigang Song
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts02138, United States
- College of Letters and Science, UCLA, Los Angeles, California90095, United States
| | - Benjamin Pingault
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts02138, United States
- QuTech, Delft University of Technology, 2600 GADelft, The Netherlands
| | - Florian Dirnberger
- Department of Physics, City College of New York, New York, New York10031, United States
| | - Hang Chi
- Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts02139, United States
- U.S. Army CCDC Army Research Laboratory, Adelphi, Maryland20783, United States
| | - Jonathan B Curtis
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts02138, United States
- College of Letters and Science, UCLA, Los Angeles, California90095, United States
| | - Rami Dana
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts02139, United States
| | - Rezlind Bushati
- Department of Physics, City College of New York, New York, New York10031, United States
- Department of Physics, The Graduate Center, City University of New York, New York, New York10016, United States
| | - Jiamin Quan
- Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas78712, United States
- Photonics Initiative, CUNY Advanced Science Research Center, New York, New York10031, United States
- Department of Electrical Engineering, City College of the City University of New York, New York, New York10031, United States
- Physics Program, Graduate Center, City University of New York, New York, New York10026, United States
| | - Lukas Dekanovsky
- Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28Prague 6, Czech Republic
| | - Zdenek Sofer
- Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28Prague 6, Czech Republic
| | - Andrea Alù
- Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas78712, United States
- Photonics Initiative, CUNY Advanced Science Research Center, New York, New York10031, United States
- Department of Electrical Engineering, City College of the City University of New York, New York, New York10031, United States
- Physics Program, Graduate Center, City University of New York, New York, New York10026, United States
| | - Vinod M Menon
- Department of Physics, City College of New York, New York, New York10031, United States
- Department of Physics, The Graduate Center, City University of New York, New York, New York10016, United States
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts02139, United States
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts02139, United States
| | - Marko Lončar
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts02138, United States
| | - Prineha Narang
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts02138, United States
- College of Letters and Science, UCLA, Los Angeles, California90095, United States
| | - Frances M Ross
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts02139, United States
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4
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Wu Y, Francisco B, Chen Z, Wang W, Zhang Y, Wan C, Han X, Chi H, Hou Y, Lodesani A, Yin G, Liu K, Cui YT, Wang KL, Moodera JS. A Van der Waals Interface Hosting Two Groups of Magnetic Skyrmions. Adv Mater 2022; 34:e2110583. [PMID: 35218078 DOI: 10.1002/adma.202110583] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 01/26/2022] [Indexed: 06/14/2023]
Abstract
Multiple magnetic skyrmion phases add an additional degree of freedom for skyrmion-based ultrahigh-density spin memory devices. Extending the field to 2D van der Waals magnets is a rewarding challenge, where the realizable degree of freedoms (e.g., thickness, twist angle, and electrical gating) and high skyrmion density result in intriguing new properties and enhanced functionality. In this work, a van der Waals interface, formed by two 2D ferromagnets Cr2 Ge2 Te6 and Fe3 GeTe2 with a Curie temperature of ≈65 and ≈205 K, respectively, hosting two groups of magnetic skyrmions, is reported. Two sets of topological Hall effect signals are observed below 6s0 K when Cr2 Ge2 Te6 is magnetically ordered. These two groups of skyrmions are directly imaged using magnetic force microscopy, and supported by micromagnetic simulations. Interestingly, the magnetic skyrmions persist in the heterostructure with zero applied magnetic field. The results are promising for the realization of skyrmionic devices based on van der Waals heterostructures hosting multiple skyrmion phases.
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Affiliation(s)
- Yingying Wu
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Brian Francisco
- Department of Physics and Astronomy, University of California, Riverside, CA, 92521, USA
| | - Zhijie Chen
- Department of Physics, Georgetown University, Washington, D.C., 20057, USA
| | - Wei Wang
- Key Laboratory of Flexible Electronics & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing, 211816, China
| | - Yu Zhang
- Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Caihua Wan
- Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Xiufeng Han
- Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Hang Chi
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- U.S. Army CCDC Army Research Laboratory, Adelphi, MD, 20783, USA
| | - Yasen Hou
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Alessandro Lodesani
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Gen Yin
- Department of Physics, Georgetown University, Washington, D.C., 20057, USA
| | - Kai Liu
- Department of Physics, Georgetown University, Washington, D.C., 20057, USA
| | - Yong-Tao Cui
- Department of Physics and Astronomy, University of California, Riverside, CA, 92521, USA
| | - Kang L Wang
- Department of Electrical and Computer Engineering, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Physics Department, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
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5
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Rocci M, Suri D, Kamra A, Takamura Y, Nemes NM, Martinez JL, Hernandez MG, Moodera JS. Large Enhancement of Critical Current in Superconducting Devices by Gate Voltage. Nano Lett 2021; 21:216-221. [PMID: 33275436 DOI: 10.1021/acs.nanolett.0c03547] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [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
Significant control over the properties of a high-carrier density superconductor via an applied electric field has been considered infeasible due to screening of the field over atomic length scales. Here, we demonstrate an enhancement of up to 30% in critical current in a back-gate tunable NbN micro- and nano superconducting bridges. Our suggested plausible mechanism of this enhancement in critical current based on surface nucleation and pinning of Abrikosov vortices is consistent with expectations and observations for type-II superconductor films with thicknesses comparable to their coherence length. Furthermore, we demonstrate an applied electric field-dependent infinite electroresistance and hysteretic resistance. Our work presents an electric field driven enhancement in the superconducting property in type-II superconductors which is a crucial step toward the understanding of field-effects on the fundamental properties of a superconductor and its exploitation for logic and memory applications in a superconductor-based low-dissipation digital computing paradigm.
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Affiliation(s)
- Mirko Rocci
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- NEST, Instituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa, Italy
| | - Dhavala Suri
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Akashdeep Kamra
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Yota Takamura
- School of Engineering, Tokyo Institute of Technology, Tokyo 152-8550, Japan
| | - Norbert M Nemes
- GFMC, Departamento de Física de Materiales, Universidad Complutense de Madrid, E-28040 Madrid, Spain
| | - Jose L Martinez
- Instituto de Ciencia de Materiales de Madrid, C.S.I.C., Cantoblanco, E-28049 Madrid, Spain
| | - Mar Garcia Hernandez
- Instituto de Ciencia de Materiales de Madrid, C.S.I.C., Cantoblanco, E-28049 Madrid, Spain
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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6
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Li Q, Li H, Xia Q, Hu Z, Zhu Y, Yan S, Ge C, Zhang Q, Wang X, Shang X, Fan S, Long Y, Gu L, Miao GX, Yu G, Moodera JS. Extra storage capacity in transition metal oxide lithium-ion batteries revealed by in situ magnetometry. Nat Mater 2021; 20:76-83. [PMID: 32807921 DOI: 10.1038/s41563-020-0756-y] [Citation(s) in RCA: 164] [Impact Index Per Article: 54.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Accepted: 07/02/2020] [Indexed: 06/11/2023]
Abstract
In lithium-ion batteries (LIBs), many promising electrodes that are based on transition metal oxides exhibit anomalously high storage capacities beyond their theoretical values. Although this phenomenon has been widely reported, the underlying physicochemical mechanism in such materials remains elusive and is still a matter of debate. In this work, we use in situ magnetometry to demonstrate the existence of strong surface capacitance on metal nanoparticles, and to show that a large number of spin-polarized electrons can be stored in the already-reduced metallic nanoparticles (that are formed during discharge at low potentials in transition metal oxide LIBs), which is consistent with a space charge mechanism. Through quantification of the surface capacitance by the variation in magnetism, we further show that this charge capacity of the surface is the dominant source of the extra capacity in the Fe3O4/Li model system, and that it also exists in CoO, NiO, FeF2 and Fe2N systems. The space charge mechanism revealed by in situ magnetometry can therefore be generalized to a broad range of transition metal compounds for which a large electron density of states is accessible, and provides pivotal guidance for creating advanced energy storage systems.
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Affiliation(s)
- Qiang Li
- College of Physics, Center for Marine Observation and Communications, Qingdao University, Qingdao, China.
- Department of Electrical and Computer Engineering and Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario, Canada.
| | - Hongsen Li
- College of Physics, Center for Marine Observation and Communications, Qingdao University, Qingdao, China.
- Materials Science and Engineering Program and Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA.
| | - Qingtao Xia
- College of Physics, Center for Marine Observation and Communications, Qingdao University, Qingdao, China
| | - Zhengqiang Hu
- College of Physics, Center for Marine Observation and Communications, Qingdao University, Qingdao, China
| | - Yue Zhu
- Materials Science and Engineering Program and Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA
| | - Shishen Yan
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, China
| | - Chen Ge
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Qinghua Zhang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Xiaoxiong Wang
- College of Physics, Center for Marine Observation and Communications, Qingdao University, Qingdao, China
| | - Xiantao Shang
- College of Physics, Center for Marine Observation and Communications, Qingdao University, Qingdao, China
| | - Shuting Fan
- College of Physics, Center for Marine Observation and Communications, Qingdao University, Qingdao, China
| | - Yunze Long
- College of Physics, Center for Marine Observation and Communications, Qingdao University, Qingdao, China
| | - Lin Gu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Guo-Xing Miao
- College of Physics, Center for Marine Observation and Communications, Qingdao University, Qingdao, China.
- Department of Electrical and Computer Engineering and Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario, Canada.
- Department of Physics, Plasma Science and Fusion Center and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Guihua Yu
- Materials Science and Engineering Program and Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA.
| | - Jagadeesh S Moodera
- Department of Physics, Plasma Science and Fusion Center and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA, USA
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7
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Affiliation(s)
- Peng Wei
- Department of Physics and Astronomy, University of California Riverside, Riverside, CA, USA.
| | - Jagadeesh S Moodera
- Physics Department, MIT, Cambridge, MA, USA.
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, MIT, Cambridge, MA, USA.
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8
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Manna S, Wei P, Xie Y, Law KT, Lee PA, Moodera JS. Signature of a pair of Majorana zero modes in superconducting gold surface states. Proc Natl Acad Sci U S A 2020; 117:8775-8782. [PMID: 32253317 PMCID: PMC7183215 DOI: 10.1073/pnas.1919753117] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Under certain conditions, a fermion in a superconductor can separate in space into two parts known as Majorana zero modes, which are immune to decoherence from local noise sources and are attractive building blocks for quantum computers. Promising experimental progress has been made to demonstrate Majorana zero modes in materials with strong spin-orbit coupling proximity coupled to superconductors. Here we report signatures of Majorana zero modes in a material platform utilizing the surface states of gold. Using scanning tunneling microscope to probe EuS islands grown on top of gold nanowires, we observe two well-separated zero-bias tunneling conductance peaks aligned along the direction of the applied magnetic field, as expected for a pair of Majorana zero modes. This platform has the advantage of having a robust energy scale and the possibility of realizing complex designs using lithographic methods.
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Affiliation(s)
- Sujit Manna
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139
- Department of Physics, Indian Institute of Technology Delhi, 110 016 New Delhi, India
| | - Peng Wei
- Department of Physics and Astronomy, University of California, Riverside, CA 92521;
| | - Yingming Xie
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong
| | - Kam Tuen Law
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong
| | - Patrick A Lee
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139;
| | - Jagadeesh S Moodera
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139;
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139
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9
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De Simoni G, Strambini E, Moodera JS, Bergeret FS, Giazotto F. Toward the Absolute Spin-Valve Effect in Superconducting Tunnel Junctions. Nano Lett 2018; 18:6369-6374. [PMID: 30248266 DOI: 10.1021/acs.nanolett.8b02723] [Citation(s) in RCA: 2] [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: 06/08/2023]
Abstract
A superconductor with a spin-split excitation spectrum behaves as an ideal ferromagnetic spin-injector in a tunneling junction. It was theoretically predicted that the combination of two such spin-split superconductors with independently tunable magnetizations may be used as an ideal absolute spin-valve. Here, we report on the first switchable superconducting spin-valve based on two EuS/Al bilayers coupled through an aluminum oxide tunnel barrier. The spin-valve shows a relative resistance change between the parallel and antiparallel configuration of the EuS layers up to 900% that demonstrates a highly spin-polarized current through the junction. Our device may be pivotal for realization of thermoelectric radiation detectors, a logical element for a memory cell in cryogenics, superconductor-based computers, and superconducting spintronics in general.
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Affiliation(s)
- Giorgio De Simoni
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore , I-56127 Pisa , Italy
| | - Elia Strambini
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore , I-56127 Pisa , Italy
| | - Jagadeesh S Moodera
- Department of Physics, Francis Bitter Magnet Lab and Plasma Science and Fusion Center , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - F Sebastian Bergeret
- Centro de Fisica de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU , Manuel de Lardizabal 5 , E-20018 San Sebastian , Spain
- Donostia International Physics Center (DIPC) , Manuel de Lardizabal 4 , E-20018 San Sebastian , Spain
| | - Francesco Giazotto
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore , I-56127 Pisa , Italy
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10
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Tang C, Song Q, Chang CZ, Xu Y, Ohnuma Y, Matsuo M, Liu Y, Yuan W, Yao Y, Moodera JS, Maekawa S, Han W, Shi J. Dirac surface state-modulated spin dynamics in a ferrimagnetic insulator at room temperature. Sci Adv 2018; 4:eaas8660. [PMID: 29868645 PMCID: PMC5983918 DOI: 10.1126/sciadv.aas8660] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/27/2017] [Accepted: 04/20/2018] [Indexed: 06/08/2023]
Abstract
This work demonstrates markedly modified spin dynamics of magnetic insulator (MI) by the spin momentum-locked Dirac surface states of the adjacent topological insulator (TI), which can be harnessed for spintronic applications. As the Bi concentration x is systematically tuned in 5-nm-thick (Bi x Sb1-x )2Te3 TI films, the weight of the surface relative to bulk states peaks at x = 0.32 when the chemical potential approaches the Dirac point. At this concentration, the Gilbert damping constant of the precessing magnetization in 10-nm-thick Y3Fe5O12 MI films in the MI/TI heterostructures is enhanced by an order of magnitude, the largest among all concentrations. In addition, the MI acquires additional strong magnetic anisotropy that favors the in-plane orientation with similar Bi concentration dependence. These extraordinary effects of the Dirac surface states distinguish TI from other materials such as heavy metals in modulating spin dynamics of the neighboring magnetic layer.
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Affiliation(s)
- Chi Tang
- Department of Physics and Astronomy, University of California, Riverside, Riverside, CA 92521, USA
| | - Qi Song
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
| | - Cui-Zu Chang
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Yadong Xu
- Department of Physics and Astronomy, University of California, Riverside, Riverside, CA 92521, USA
| | - Yuichi Ohnuma
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Ibaraki, Japan
| | - Mamoru Matsuo
- Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Ibaraki, Japan
- Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Miyagi, Japan
| | - Yawen Liu
- Department of Physics and Astronomy, University of California, Riverside, Riverside, CA 92521, USA
| | - Wei Yuan
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
| | - Yunyan Yao
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
| | - Jagadeesh S. Moodera
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Sadamichi Maekawa
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Wei Han
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
| | - Jing Shi
- Department of Physics and Astronomy, University of California, Riverside, Riverside, CA 92521, USA
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11
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Zhao W, Li M, Chang CZ, Jiang J, Wu L, Liu C, Moodera JS, Zhu Y, Chan MHW. Direct imaging of electron transfer and its influence on superconducting pairing at FeSe/SrTiO 3 interface. Sci Adv 2018; 4:eaao2682. [PMID: 29556528 PMCID: PMC5856486 DOI: 10.1126/sciadv.aao2682] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2017] [Accepted: 02/07/2018] [Indexed: 05/31/2023]
Abstract
The exact mechanism responsible for the significant enhancement of the superconducting transition temperature (Tc) of monolayer iron selenide (FeSe) films on SrTiO3 (STO) over that of bulk FeSe is an open issue. We present the results of a coordinated study of electrical transport, low temperature electron energy-loss spectroscopy (EELS), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurements on FeSe/STO films of different thicknesses. HAADF-STEM imaging together with EELS mapping across the FeSe/STO interface shows direct evidence of electrons transferred from STO to the FeSe layer. The transferred electrons were found to accumulate within the first two atomic layers of the FeSe films near the STO substrate. An additional Se layer is also resolved to reside between the FeSe film and the TiO x -terminated STO substrate. Our transport results found that a positive backgate applied from STO is particularly effective in enhancing Tc of the films while minimally changing the carrier density. This increase in Tc is due to the positive backgate that "pulls" the transferred electrons in FeSe films closer to the interface and thus enhances their coupling to interfacial phonons and also the electron-electron interaction within FeSe films.
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Affiliation(s)
- Weiwei Zhao
- Center for Nanoscale Science and Department of Physics, Pennsylvania State University, University Park, PA 16802–6300, USA
- State Key Laboratory of Advanced Welding and Joining and Research Center of Flexible Printed Electronic Technology, Harbin Institute of Technology, Shenzhen 518055, People’s Republic of China
| | - Mingda Li
- Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Cui-Zu Chang
- Center for Nanoscale Science and Department of Physics, Pennsylvania State University, University Park, PA 16802–6300, USA
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Jue Jiang
- Center for Nanoscale Science and Department of Physics, Pennsylvania State University, University Park, PA 16802–6300, USA
| | - Lijun Wu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Chaoxing Liu
- Center for Nanoscale Science and Department of Physics, Pennsylvania State University, University Park, PA 16802–6300, USA
| | - Jagadeesh S. Moodera
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Yimei Zhu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Moses H. W. Chan
- Center for Nanoscale Science and Department of Physics, Pennsylvania State University, University Park, PA 16802–6300, USA
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12
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Richardson CL, Devine-Stoneman JM, Divitini G, Vickers ME, Chang CZ, Amado M, Moodera JS, Robinson JWA. Structural properties of thin-film ferromagnetic topological insulators. Sci Rep 2017; 7:12061. [PMID: 28935891 PMCID: PMC5608805 DOI: 10.1038/s41598-017-12237-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2017] [Accepted: 09/06/2017] [Indexed: 11/28/2022] Open
Abstract
We present a comprehensive study of the crystal structure of the thin-film, ferromagnetic topological insulator (Bi, Sb)2−xVxTe3. The dissipationless quantum anomalous Hall edge states it manifests are of particular interest for spintronics, as a natural spin filter or pure spin source, and as qubits for topological quantum computing. For ranges typically used in experiments, we investigate the effect of doping, substrate choice and film thickness on the (Bi, Sb)2Te3 unit cell using high-resolution X-ray diffractometry. Scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements provide local structural and interfacial information. We find that the unit cell is unaffected in-plane by vanadium doping changes, and remains unchanged over a thickness range of 4–10 quintuple layers (1 QL ≈ 1 nm). The in-plane lattice parameter (a) also remains the same in films grown on different substrate materials. However, out-of-plane the c-axis increases with the doping level and thicknesses >10 QL, and is potentially reduced in films grown on Si (1 1 1).
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Affiliation(s)
- C L Richardson
- University of Cambridge, Department of Materials Science and Metallurgy, Cambridge, CB3 0FS, United Kingdom
| | - J M Devine-Stoneman
- University of Cambridge, Department of Materials Science and Metallurgy, Cambridge, CB3 0FS, United Kingdom
| | - G Divitini
- University of Cambridge, Department of Materials Science and Metallurgy, Cambridge, CB3 0FS, United Kingdom
| | - M E Vickers
- University of Cambridge, Department of Materials Science and Metallurgy, Cambridge, CB3 0FS, United Kingdom
| | - C-Z Chang
- Massachusetts Institute of Technology, Francis Bitter National Magnet Laboratory, Cambridge, MA, 02139, USA.,Pennsylvania State University, Department of Physics, State College, PA, 16802-6300, USA
| | - M Amado
- University of Cambridge, Department of Materials Science and Metallurgy, Cambridge, CB3 0FS, United Kingdom
| | - J S Moodera
- Massachusetts Institute of Technology, Francis Bitter National Magnet Laboratory, Cambridge, MA, 02139, USA.,Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - J W A Robinson
- University of Cambridge, Department of Materials Science and Metallurgy, Cambridge, CB3 0FS, United Kingdom.
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13
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Tang C, Chang CZ, Zhao G, Liu Y, Jiang Z, Liu CX, McCartney MR, Smith DJ, Chen T, Moodera JS, Shi J. Above 400-K robust perpendicular ferromagnetic phase in a topological insulator. Sci Adv 2017; 3:e1700307. [PMID: 28691097 PMCID: PMC5482549 DOI: 10.1126/sciadv.1700307] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 04/21/2017] [Indexed: 05/23/2023]
Abstract
The quantum anomalous Hall effect (QAHE) that emerges under broken time-reversal symmetry in topological insulators (TIs) exhibits many fascinating physical properties for potential applications in nanoelectronics and spintronics. However, in transition metal-doped TIs, the only experimentally demonstrated QAHE system to date, the QAHE is lost at practically relevant temperatures. This constraint is imposed by the relatively low Curie temperature (Tc) and inherent spin disorder associated with the random magnetic dopants. We demonstrate drastically enhanced Tc by exchange coupling TIs to Tm3Fe5O12, a high-Tc magnetic insulator with perpendicular magnetic anisotropy. Signatures showing that the TI surface states acquire robust ferromagnetism are revealed by distinct squared anomalous Hall hysteresis loops at 400 K. Point-contact Andreev reflection spectroscopy confirms that the TI surface is spin-polarized. The greatly enhanced Tc, absence of spin disorder, and perpendicular anisotropy are all essential to the occurrence of the QAHE at high temperatures.
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Affiliation(s)
- Chi Tang
- Department of Physics and Astronomy, University of California, Riverside, Riverside, CA 92521, USA
| | - Cui-Zu Chang
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Gejian Zhao
- Department of Physics, Arizona State University, Tempe, AZ 85287, USA
| | - Yawen Liu
- Department of Physics and Astronomy, University of California, Riverside, Riverside, CA 92521, USA
| | - Zilong Jiang
- Department of Physics and Astronomy, University of California, Riverside, Riverside, CA 92521, USA
| | - Chao-Xing Liu
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | | | - David J. Smith
- Department of Physics, Arizona State University, Tempe, AZ 85287, USA
| | - Tingyong Chen
- Department of Physics, Arizona State University, Tempe, AZ 85287, USA
| | - Jagadeesh S. Moodera
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Jing Shi
- Department of Physics and Astronomy, University of California, Riverside, Riverside, CA 92521, USA
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14
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Chang CZ, Zhao W, Li J, Jain JK, Liu C, Moodera JS, Chan MHW. Observation of the Quantum Anomalous Hall Insulator to Anderson Insulator Quantum Phase Transition and its Scaling Behavior. Phys Rev Lett 2016; 117:126802. [PMID: 27689289 DOI: 10.1103/physrevlett.117.126802] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2016] [Indexed: 06/06/2023]
Abstract
Fundamental insight into the nature of the quantum phase transition from a superconductor to an insulator in two dimensions, or from one plateau to the next or to an insulator in the quantum Hall effect, has been revealed through the study of its scaling behavior. Here, we report on the experimental observation of a quantum phase transition from a quantum-anomalous-Hall insulator to an Anderson insulator in a magnetic topological insulator by tuning the chemical potential. Our experiment demonstrates the existence of scaling behavior from which we extract the critical exponent for this quantum phase transition. We expect that our work will motivate much further investigation of many properties of quantum phase transition in this new context.
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Affiliation(s)
- Cui-Zu Chang
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Weiwei Zhao
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Jian Li
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - J K Jain
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Chaoxing Liu
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Moses H W Chan
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
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15
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Li W, Claassen M, Chang CZ, Moritz B, Jia T, Zhang C, Rebec S, Lee JJ, Hashimoto M, Lu DH, Moore RG, Moodera JS, Devereaux TP, Shen ZX. Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb)2Te3 film. Sci Rep 2016; 6:32732. [PMID: 27599406 PMCID: PMC5013448 DOI: 10.1038/srep32732] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 08/08/2016] [Indexed: 11/09/2022] Open
Abstract
The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb)2Te3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb)2Te3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Dirac point. Our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy.
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Affiliation(s)
- W Li
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA
| | - M Claassen
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA
| | - Cui-Zu Chang
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - B Moritz
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA
| | - T Jia
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA.,Departments of Physics and Applied Physics, and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
| | - C Zhang
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA
| | - S Rebec
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA.,Departments of Physics and Applied Physics, and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
| | - J J Lee
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA.,Departments of Physics and Applied Physics, and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
| | - M Hashimoto
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - D-H Lu
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - R G Moore
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA
| | - J S Moodera
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - T P Devereaux
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA.,Departments of Physics and Applied Physics, and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
| | - Z-X Shen
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA.,Departments of Physics and Applied Physics, and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
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16
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Huang D, Webb TA, Song CL, Chang CZ, Moodera JS, Kaxiras E, Hoffman JE. Dumbbell Defects in FeSe Films: A Scanning Tunneling Microscopy and First-Principles Investigation. Nano Lett 2016; 16:4224-4229. [PMID: 27282020 DOI: 10.1021/acs.nanolett.6b01163] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [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 properties of iron-based superconductors (Fe-SCs) can be varied dramatically with the introduction of dopants and atomic defects. As a pressing example, FeSe, parent phase of the highest-Tc Fe-SC, exhibits prevalent defects with atomic-scale "dumbbell" signatures as imaged by scanning tunneling microscopy (STM). These defects spoil superconductivity when their concentration exceeds 2.5%. Resolving their chemical identity is a prerequisite to applications such as nanoscale patterning of superconducting/nonsuperconducting regions in FeSe as well as fundamental questions such as the mechanism of superconductivity and the path by which the defects destroy it. We use STM and density functional theory to characterize and identify the dumbbell defects. In contrast to previous speculations about Se adsorbates or substitutions, we find that an Fe-site vacancy is the most energetically favorable defect in Se-rich conditions and reproduces our observed STM signature. Our calculations shed light more generally on the nature of Se capping, the removal of Fe vacancies via annealing, and their ordering into a √5 × √5 superstructure in FeSe and related alkali-doped compounds.
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Affiliation(s)
| | - Tatiana A Webb
- Department of Physics & Astronomy, University of British Columbia , Vancouver, British Columbia V6T 1Z1, Canada
| | | | | | | | | | - Jennifer E Hoffman
- Department of Physics & Astronomy, University of British Columbia , Vancouver, British Columbia V6T 1Z1, Canada
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17
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Wei P, Lee S, Lemaitre F, Pinel L, Cutaia D, Cha W, Katmis F, Zhu Y, Heiman D, Hone J, Moodera JS, Chen CT. Strong interfacial exchange field in the graphene/EuS heterostructure. Nat Mater 2016; 15:711-6. [PMID: 27019382 DOI: 10.1038/nmat4603] [Citation(s) in RCA: 97] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 02/22/2016] [Indexed: 05/20/2023]
Abstract
Exploiting 2D materials for spintronic applications can potentially realize next-generation devices featuring low power consumption and quantum operation capability. The magnetic exchange field (MEF) induced by an adjacent magnetic insulator enables efficient control of local spin generation and spin modulation in 2D devices without compromising the delicate material structures. Using graphene as a prototypical 2D system, we demonstrate that its coupling to the model magnetic insulator (EuS) produces a substantial MEF (>14 T) with the potential to reach hundreds of tesla, which leads to orders-of-magnitude enhancement of the spin signal originating from the Zeeman spin Hall effect. Furthermore, the new ferromagnetic ground state of Dirac electrons resulting from the strong MEF may give rise to quantized spin-polarized edge transport. The MEF effect shown in our graphene/EuS devices therefore provides a key functionality for future spin logic and memory devices based on emerging 2D materials in classical and quantum information processing.
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Affiliation(s)
- Peng Wei
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Sunwoo Lee
- IBM TJ Watson Research Center, Yorktown Heights, New York 10598, USA
- Electrical Engineering Department, Columbia University, New York, New York 10027, USA
| | - Florian Lemaitre
- IBM TJ Watson Research Center, Yorktown Heights, New York 10598, USA
- Institut polytechnique de Grenoble, F38031 Grenoble Cedex 1, France
| | - Lucas Pinel
- IBM TJ Watson Research Center, Yorktown Heights, New York 10598, USA
- Institut polytechnique de Grenoble, F38031 Grenoble Cedex 1, France
| | - Davide Cutaia
- IBM TJ Watson Research Center, Yorktown Heights, New York 10598, USA
- IBM Zurich Research Laboratory, Säumerstrasse 4, CH- 8803 Rüschlikon, Switzerland
| | - Wujoon Cha
- Mechanical Engineering Department, Columbia University, New York, New York 10027, USA
| | - Ferhat Katmis
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Yu Zhu
- IBM TJ Watson Research Center, Yorktown Heights, New York 10598, USA
| | - Donald Heiman
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
| | - James Hone
- Mechanical Engineering Department, Columbia University, New York, New York 10027, USA
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Ching-Tzu Chen
- IBM TJ Watson Research Center, Yorktown Heights, New York 10598, USA
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18
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Lee C, Katmis F, Jarillo-Herrero P, Moodera JS, Gedik N. Direct measurement of proximity-induced magnetism at the interface between a topological insulator and a ferromagnet. Nat Commun 2016; 7:12014. [PMID: 27344976 PMCID: PMC4931222 DOI: 10.1038/ncomms12014] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 05/23/2016] [Indexed: 01/09/2023] Open
Abstract
When a topological insulator (TI) is in contact with a ferromagnet, both time-reversal and inversion symmetries are broken at the interface. An energy gap is formed at the TI surface, and its electrons gain a net magnetic moment through short-range exchange interactions. Magnetic TIs can host various exotic quantum phenomena, such as massive Dirac fermions, Majorana fermions, the quantum anomalous Hall effect and chiral edge currents along the domain boundaries. However, selective measurement of induced magnetism at the buried interface has remained a challenge. Using magnetic second-harmonic generation, we directly probe both the in-plane and out-of-plane magnetizations induced at the interface between the ferromagnetic insulator (FMI) EuS and the three-dimensional TI Bi2Se3. Our findings not only allow characterizing magnetism at the TI-FMI interface but also lay the groundwork for imaging magnetic domains and domain boundaries at the magnetic TI surfaces.
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Affiliation(s)
- Changmin Lee
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Ferhat Katmis
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.,Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.,Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Pablo Jarillo-Herrero
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Jagadeesh S Moodera
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.,Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.,Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Nuh Gedik
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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19
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Wei P, Katmis F, Chang CZ, Moodera JS. Induced Superconductivity and Engineered Josephson Tunneling Devices in Epitaxial (111)-Oriented Gold/Vanadium Heterostructures. Nano Lett 2016; 16:2714-2719. [PMID: 26943807 DOI: 10.1021/acs.nanolett.6b00361] [Citation(s) in RCA: 2] [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: 06/05/2023]
Abstract
We report a unique experimental approach to create topological superconductors by inducing superconductivity into epitaxial metallic thin film with strong spin-orbit coupling. Utilizing molecular beam epitaxy technique under ultrahigh vacuum conditions, we are able to achieve (111) oriented single phase of gold (Au) thin film grown on a well-oriented vanadium (V) s-wave superconductor film with clean interface. We obtained atomically smooth Au thin films with thicknesses even down to below a nanometer showing near-ideal surface quality. The as-grown V/Au bilayer heterostructure exhibits superconducting transition at around 3.9 K. Clear Josephson tunneling and Andreev reflection are observed in S-I-S tunnel junctions fabricated from the epitaxial bilayers. The barrier thickness dependent tunneling and the associated subharmonic gap structures (SGS) confirmed the induced superconductivity in Au (111), paving the way for engineering thin film heterostructures based on p-wave superconductivity and nano devices exploiting Majorana Fermions for quantum computing.
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Affiliation(s)
- Peng Wei
- Francis Bitter Magnet Laboratory, ‡Department of Physics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
| | - Ferhat Katmis
- Francis Bitter Magnet Laboratory, ‡Department of Physics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
| | - Cui-Zu Chang
- Francis Bitter Magnet Laboratory, ‡Department of Physics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Laboratory, ‡Department of Physics, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
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20
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Jiang Z, Chang CZ, Tang C, Wei P, Moodera JS, Shi J. Independent Tuning of Electronic Properties and Induced Ferromagnetism in Topological Insulators with Heterostructure Approach. Nano Lett 2015; 15:5835-5840. [PMID: 26288309 DOI: 10.1021/acs.nanolett.5b01905] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The quantum anomalous Hall effect (QAHE) has been recently demonstrated in Cr- and V-doped three-dimensional topological insulators (TIs) at temperatures below 100 mK. In those materials, the spins of unfilled d-electrons in the transition metal dopants are exchange coupled to develop a long-range ferromagnetic order, which is essential for realizing QAHE. However, the addition of random dopants does not only introduce excess charge carriers that require readjusting the Bi/Sb ratio, but also unavoidably introduces paramagnetic spins that can adversely affect the chiral edge transport in QAHE. In this work, we show a heterostructure approach to independently tune the electronic and magnetic properties of the topological surface states in (BixSb1-x)2Te3 without resorting to random doping of transition metal elements. In heterostructures consisting of a thin (BixSb1-x)2Te3 TI film and yttrium iron garnet (YIG), a high Curie temperature (∼550 K) magnetic insulator, we find that the TI surface in contact with YIG becomes ferromagnetic via proximity coupling which is revealed by the anomalous Hall effect (AHE). The Curie temperature of the magnetized TI surface ranges from 20 to 150 K but is uncorrelated with the Bi fraction x in (BixSb1-x)2Te3. In contrast, as x is varied, the AHE resistivity scales with the longitudinal resistivity. In this approach, we decouple the electronic properties from the induced ferromagnetism in TI. The independent optimization provides a pathway for realizing QAHE at higher temperatures, which is important for novel spintronic device applications.
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Affiliation(s)
- Zilong Jiang
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | | | - Chi Tang
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | | | | | - Jing Shi
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
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21
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Wang YH, Kirtley JR, Katmis F, Jarillo-Herrero P, Moodera JS, Moler KA. RETRACTED: Observation of chiral currents at the magnetic domain boundary of a topological insulator. Science 2015; 349:948-52. [PMID: 26272905 DOI: 10.1126/science.aaa0508] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Accepted: 07/29/2015] [Indexed: 02/23/2024]
Abstract
A magnetic domain boundary on the surface of a three-dimensional topological insulator is predicted to host a chiral edge state, but direct demonstration is challenging. We used a scanning superconducting quantum interference device to show that current in a magnetized topological insulator heterostructure (EuS/Bi2Se3) flows at the edge when the Fermi level is gate-tuned to the surface band gap. We further induced micrometer-scale magnetic structures on the heterostructure and detected a chiral edge current at the magnetic domain boundary. The chirality of the current was determined by magnetization of the surrounding domain, and its magnitude by the local chemical potential rather than the applied current. Such magnetic structures provide a platform for detecting topological magnetoelectric effects and may enable progress in quantum information processing and spintronics.
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Affiliation(s)
- Y H Wang
- Department of Physics and Applied Physics, Stanford University, Stanford, CA 94305, USA. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
| | - J R Kirtley
- Department of Physics and Applied Physics, Stanford University, Stanford, CA 94305, USA
| | - F Katmis
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - P Jarillo-Herrero
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - J S Moodera
- Francis Bitter Magnet Laboratory and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - K A Moler
- Department of Physics and Applied Physics, Stanford University, Stanford, CA 94305, USA. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
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22
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Li M, Chang CZ, Kirby BJ, Jamer ME, Cui W, Wu L, Wei P, Zhu Y, Heiman D, Li J, Moodera JS. Proximity-Driven Enhanced Magnetic Order at Ferromagnetic-Insulator-Magnetic-Topological-Insulator Interface. Phys Rev Lett 2015; 115:087201. [PMID: 26340203 DOI: 10.1103/physrevlett.115.087201] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Indexed: 06/05/2023]
Abstract
Magnetic exchange driven proximity effect at a magnetic-insulator-topological-insulator (MI-TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. Here we report a dramatic enhancement of proximity exchange coupling in the MI/magnetic-TI EuS/Sb(2-x)V(x)Te3 hybrid heterostructure, where V doping is used to drive the TI (Sb2Te3) magnetic. We observe an artificial antiferromagneticlike structure near the MI-TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping in a hybrid heterostructure provides insights into the engineering of magnetic ordering.
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Affiliation(s)
- Mingda Li
- Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Fracsis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Cui-Zu Chang
- Fracsis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Brian J Kirby
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Michelle E Jamer
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
| | - Wenping Cui
- Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA
| | - Lijun Wu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Peng Wei
- Fracsis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Yimei Zhu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Don Heiman
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
| | - Ju Li
- Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Material Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Jagadeesh S Moodera
- Fracsis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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23
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Chang CZ, Zhao W, Kim DY, Wei P, Jain JK, Liu C, Chan MHW, Moodera JS. Zero-Field Dissipationless Chiral Edge Transport and the Nature of Dissipation in the Quantum Anomalous Hall State. Phys Rev Lett 2015; 115:057206. [PMID: 26274440 DOI: 10.1103/physrevlett.115.057206] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Indexed: 06/04/2023]
Abstract
The quantum anomalous Hall (QAH) effect is predicted to possess, at a zero magnetic field, chiral edge channels that conduct a spin polarized current without dissipation. While edge channels have been observed in previous experimental studies of the QAH effect, their dissipationless nature at a zero magnetic field has not been convincingly demonstrated. By a comprehensive experimental study of the gate and temperature dependences of local and nonlocal magnetoresistance, we unambiguously establish the dissipationless edge transport. By studying the onset of dissipation, we also identify the origin of dissipative channels and clarify the surprising observation that the critical temperature of the QAH effect is 2 orders of magnitude smaller than the Curie temperature of ferromagnetism.
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Affiliation(s)
- Cui-Zu Chang
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Weiwei Zhao
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Duk Y Kim
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Peng Wei
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - J K Jain
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Chaoxing Liu
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Moses H W Chan
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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24
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Huang D, Song CL, Webb TA, Fang S, Chang CZ, Moodera JS, Kaxiras E, Hoffman JE. Revealing the Empty-State Electronic Structure of Single-Unit-Cell FeSe/SrTiO3. Phys Rev Lett 2015; 115:017002. [PMID: 26182116 DOI: 10.1103/physrevlett.115.017002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Indexed: 06/04/2023]
Abstract
We use scanning tunneling spectroscopy to investigate the filled and empty electronic states of superconducting single-unit-cell FeSe deposited on SrTiO3(001). We map the momentum-space band structure by combining quasiparticle interference imaging with decay length spectroscopy. In addition to quantifying the filled-state bands, we discover a Γ-centered electron pocket 75 meV above the Fermi energy. Our density functional theory calculations show the orbital nature of empty states at Γ and explain how the Se height is a key tuning parameter of their energies, with broad implications for electronic properties.
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Affiliation(s)
- Dennis Huang
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Can-Li Song
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Tatiana A Webb
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Shiang Fang
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Cui-Zu Chang
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Efthimios Kaxiras
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Jennifer E Hoffman
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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25
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Chang CZ, Zhao W, Kim DY, Zhang H, Assaf BA, Heiman D, Zhang SC, Liu C, Chan MHW, Moodera JS. High-precision realization of robust quantum anomalous Hall state in a hard ferromagnetic topological insulator. Nat Mater 2015; 14:473-7. [PMID: 25730394 DOI: 10.1038/nmat4204] [Citation(s) in RCA: 250] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2014] [Accepted: 12/19/2014] [Indexed: 05/13/2023]
Abstract
The discovery of the quantum Hall (QH) effect led to the realization of a topological electronic state with dissipationless currents circulating in one direction along the edge of a two-dimensional electron layer under a strong magnetic field. The quantum anomalous Hall (QAH) effect shares a similar physical phenomenon to that of the QH effect, whereas its physical origin relies on the intrinsic spin-orbit coupling and ferromagnetism. Here, we report the experimental observation of the QAH state in V-doped (Bi,Sb)2Te3 films with the zero-field longitudinal resistance down to 0.00013 ± 0.00007h/e(2) (~3.35 ± 1.76 Ω), Hall conductance reaching 0.9998 ± 0.0006e(2)/h and the Hall angle becoming as high as 89.993° ± 0.004° at T = 25 mK. A further advantage of this system comes from the fact that it is a hard ferromagnet with a large coercive field (Hc > 1.0 T) and a relative high Curie temperature. This realization of a robust QAH state in hard ferromagnetic topological insulators (FMTIs) is a major step towards dissipationless electronic applications in the absence of external fields.
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Affiliation(s)
- Cui-Zu Chang
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Weiwei Zhao
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Duk Y Kim
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Haijun Zhang
- Department of Physics, Stanford University, Stanford, California 94305-4045, USA
| | - Badih A Assaf
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
| | - Don Heiman
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
| | - Shou-Cheng Zhang
- Department of Physics, Stanford University, Stanford, California 94305-4045, USA
| | - Chaoxing Liu
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Moses H W Chan
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Jagadeesh S Moodera
- 1] Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA [2] Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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26
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Li M, Chang CZ, Wu L, Tao J, Zhao W, Chan MHW, Moodera JS, Li J, Zhu Y. Experimental verification of the van Vleck nature of long-range ferromagnetic order in the vanadium-doped three-dimensional topological insulator Sb(2)Te(3). Phys Rev Lett 2015; 114:146802. [PMID: 25910148 DOI: 10.1103/physrevlett.114.146802] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Indexed: 06/04/2023]
Abstract
We demonstrate by high resolution low temperature electron energy loss spectroscopy (EELS) measurements that the long range ferromagnetic (FM) order in the vanadium- (V-)doped topological insulator Sb_{2}Te_{3} has the nature of van Vleck-type ferromagnetism. The positions and the relative amplitudes of two core-level peaks (L_{3} and L_{2}) of the V EELS spectrum show unambiguous change when the sample is cooled from room temperature to T=10 K. Magnetotransport and comparison of the measured and simulated EELS spectra confirm that these changes originate from the onset of FM order. Crystal field analysis indicates that in V-doped Sb_{2}Te_{3}, partially filled core states contribute to the FM order. Since van Vleck magnetism is a result of summing over all states, this magnetization of core level verifies the van Vleck-type ferromagnetism in a direct manner.
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Affiliation(s)
- Mingda Li
- Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Cui-Zu Chang
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Lijun Wu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Jing Tao
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Weiwei Zhao
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Moses H W Chan
- The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Jagadeesh S Moodera
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Ju Li
- Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Material Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Yimei Zhu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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27
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Abstract
Magnetic semiconductors with unique spin-filtering property and the ability to create excessive internal magnetic fields can open myriads of new phenomena.
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Affiliation(s)
- Guo-Xing Miao
- Institute for Quantum
- Computing and Department of Electrical and Computer Engineering
- University of Waterloo
- Waterloo
- Canada
| | - Jagadeesh S. Moodera
- Francis Bitter Magnet Laboratory
- Massachusetts Institute of Technology
- Cambridge
- USA
- Department of Physics
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28
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Ciudad D, Gobbi M, Kinane CJ, Eich M, Moodera JS, Hueso LE. Sign control of magnetoresistance through chemically engineered interfaces. Adv Mater 2014; 26:7561-7567. [PMID: 25339373 DOI: 10.1002/adma.201401283] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2014] [Revised: 08/11/2014] [Indexed: 06/04/2023]
Abstract
Chemically engineered interfaces are shown to produce inversions of the magnetoresistance in spintronic devices including lithium fluoride interlayers. This behavior is explained by the formation of anti-ferromagnetic difluoride layers. By changing the order of deposition of the different materials, the sign of the magnetoresistance can be deterministically controlled both in organic spin valves and in inorganic magnetic tunnel junctions.
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Affiliation(s)
- David Ciudad
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA; CIC nanoGUNE, Tolosa Hiribidea 76, 20018, Donostia-San Sebastian, Spain
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29
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Wei P, Katmis F, Assaf BA, Steinberg H, Jarillo-Herrero P, Heiman D, Moodera JS. Exchange-coupling-induced symmetry breaking in topological insulators. Phys Rev Lett 2013; 110:186807. [PMID: 23683236 DOI: 10.1103/physrevlett.110.186807] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Indexed: 05/22/2023]
Abstract
An exchange gap in the Dirac surface states of a topological insulator (TI) is necessary for observing the predicted unique features such as the topological magnetoelectric effect as well as to confine Majorana fermions. We experimentally demonstrate proximity-induced ferromagnetism in a TI, combining a ferromagnetic insulator EuS layer with Bi(2)Se(3), without introducing defects. By magnetic and magnetotransport studies, including anomalous Hall effect and magnetoresistance measurements, we show the emergence of a ferromagnetic phase in TI, a step forward in unveiling their exotic properties.
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Affiliation(s)
- Peng Wei
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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30
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Raman KV, Kamerbeek AM, Mukherjee A, Atodiresei N, Sen TK, Lazić P, Caciuc V, Michel R, Stalke D, Mandal SK, Blügel S, Münzenberg M, Moodera JS. Interface-engineered templates for molecular spin memory devices. Nature 2013; 493:509-13. [PMID: 23344361 DOI: 10.1038/nature11719] [Citation(s) in RCA: 343] [Impact Index Per Article: 31.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2012] [Accepted: 10/23/2012] [Indexed: 11/09/2022]
Abstract
The use of molecular spin state as a quantum of information for storage, sensing and computing has generated considerable interest in the context of next-generation data storage and communication devices, opening avenues for developing multifunctional molecular spintronics. Such ideas have been researched extensively, using single-molecule magnets and molecules with a metal ion or nitrogen vacancy as localized spin-carrying centres for storage and for realizing logic operations. However, the electronic coupling between the spin centres of these molecules is rather weak, which makes construction of quantum memory registers a challenging task. In this regard, delocalized carbon-based radical species with unpaired spin, such as phenalenyl, have shown promise. These phenalenyl moieties, which can be regarded as graphene fragments, are formed by the fusion of three benzene rings and belong to the class of open-shell systems. The spin structure of these molecules responds to external stimuli (such as light, and electric and magnetic fields), which provides novel schemes for performing spin memory and logic operations. Here we construct a molecular device using such molecules as templates to engineer interfacial spin transfer resulting from hybridization and magnetic exchange interaction with the surface of a ferromagnet; the device shows an unexpected interfacial magnetoresistance of more than 20 per cent near room temperature. Moreover, we successfully demonstrate the formation of a nanoscale magnetic molecule with a well-defined magnetic hysteresis on ferromagnetic surfaces. Owing to strong magnetic coupling with the ferromagnet, such independent switching of an adsorbed magnetic molecule has been unsuccessful with single-molecule magnets. Our findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development.
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Affiliation(s)
- Karthik V Raman
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Massachusetts 02139, USA
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31
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Li B, Roschewsky N, Assaf BA, Eich M, Epstein-Martin M, Heiman D, Münzenberg M, Moodera JS. Superconducting spin switch with infinite magnetoresistance induced by an internal exchange field. Phys Rev Lett 2013; 110:097001. [PMID: 23496737 DOI: 10.1103/physrevlett.110.097001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Indexed: 06/01/2023]
Abstract
A theoretical prediction by de Gennes suggests that the resistance in a FI/S/FI (where FI is a ferromagnetic insulator, and S is a superconductor) structure will depend on the magnetization direction of the two FI layers. We report a magnetotransport measurement in a EuS/Al/EuS structure, showing that an infinite magnetoresistance can be produced by tuning the internal exchange field at the FI/S interface. This proximity effect at the interface can be suppressed by an Al(2)O(3) barrier as thin as 0.3 nm, showing the extreme confinement of the interaction to the interface giving rise to the demonstrated phenomena.
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Affiliation(s)
- Bin Li
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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32
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Assaf BA, Cardinal T, Wei P, Katmis F, Moodera JS, Heiman D. Modified electrical transport probe design for standard magnetometer. Rev Sci Instrum 2012; 83:033904. [PMID: 22462935 DOI: 10.1063/1.3697998] [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] [Indexed: 05/31/2023]
Abstract
Making electrical transport measurements on a material is often a time consuming process that involves testing a large number of samples. It is thus inconvenient to wire up and rewire samples onto a sample probe. We therefore present a method of modifying Quantum Design's MPMS SQUID magnetometer transport probe that simplifies the process of sample mounting. One of the difficulties to overcome is the small diameter of the sample space. A small socket is designed and mounted on the probe so that various samples mounted on individual headers can be readily exchanged in the socket. We also present some test results on the topological insulator Bi(2)Te(2)Se using the modified probe.
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Affiliation(s)
- B A Assaf
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
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33
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Walter M, Walowski J, Zbarsky V, Münzenberg M, Schäfers M, Ebke D, Reiss G, Thomas A, Peretzki P, Seibt M, Moodera JS, Czerner M, Bachmann M, Heiliger C. Seebeck effect in magnetic tunnel junctions. Nat Mater 2011; 10:742-746. [PMID: 21785418 DOI: 10.1038/nmat3076] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Accepted: 06/20/2011] [Indexed: 05/31/2023]
Abstract
Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, that is, the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge-based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel junction. In this respect, it is the analogue to the tunnelling magnetoresistance. The Seebeck coefficients in parallel and antiparallel configurations are of the order of the voltages known from the charge-Seebeck effect. The size and sign of the effect can be controlled by the composition of the electrodes' atomic layers adjacent to the barrier and the temperature. The geometric centre of the electronic density of states relative to the Fermi level determines the size of the Seebeck effect. Experimentally, we realized 8.8% magneto-Seebeck effect, which results from a voltage change of about -8.7 μV K⁻¹ from the antiparallel to the parallel direction close to the predicted value of -12.1 μV K⁻¹. In contrast to the spin-Seebeck effect, it can be measured as a voltage change directly without conversion of a spin current.
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34
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Sierra JF, Pryadun VV, Russek SE, García-Hernández M, Mompean F, Rozada R, Chubykalo-Fesenko O, Snoeck E, Miao GX, Moodera JS, Aliev FG. Interface and temperature dependent magnetic properties in permalloy thin films and tunnel junction structures. J Nanosci Nanotechnol 2011; 11:7653-7664. [PMID: 22097470 DOI: 10.1166/jnn.2011.4754] [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] [Indexed: 05/31/2023]
Abstract
Magnetization dynamics and field dependent magnetization of different devices based on 25-30 nm thick Permalloy (Py) films: such as single Py layers (Py/MgO; Py/CoFeB/Al2O3) and Py inserted as a magnetic layer in magnetic tunnel junctions (Py/CoFe/Al2O3/CoFe; Py/CoFeB/Al2O3/CoFe; Py/MgO/Fe) have been extensively studied within a temperature range between 300 K down to 5 K. The dynamic response was investigated in the linear regime measuring the ferromagnetic resonance response of the Py layers using broadband vector network analyzer technique. Both the static and the dynamic properties suggest the possible presence of a thermally induced spin reorientation transition in the Py interface at temperatures around 60 K in all the samples investigated. It seems, however, that the details of the interface between Py and the hardening ferromagnet/insulator structure, the atomic structure of Py layers (amorphous vs. textured) as well as the presence of dipolar coupling through the insulating barrier in the magnetic tunnel junction structures could strongly influence this low temperature reorientation transition. Our conclusions are indirectly supported by structural characterization of the samples by means of X-Ray diffraction and high resolution transmission electron microscopy techniques. Micromagnetic simulations indicate the possibility of strongly enhanced surface anisotropy in thin Py films over CoFe or CoFeB underlayers. Comparison of the simulations with experimental results also shows that the thermally-induced spin reorientation transition could be influenced by the presence of strong disorder at the surface.
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Affiliation(s)
- J F Sierra
- Departamento Física de la Materia Condensada C-III and Instituto "Nicolás Cabrera" Ciencia de Materiales, Universidad Autónoma de Madrid, 28049 Madrid, Spain
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Park YJ, Hickey MC, Van Veenhuizen MJ, Chang J, Heiman D, Perry CH, Moodera JS. Efficient spin transfer phenomena in Fe/MgO/GaAs structure. J Phys Condens Matter 2011; 23:116002. [PMID: 21358034 DOI: 10.1088/0953-8984/23/11/116002] [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] [Indexed: 05/30/2023]
Abstract
The efficiency of spin polarized charge transfer was investigated in an Fe/MgO tunnel barrier/GaAs based structure using spin dependent photocurrent measurements, whereby a spin imbalance in carrier population was generated in the GaAs by circularly polarized light. The dominance of tunneling transport processes over Schottky emission gave rise to a high spin transfer efficiency of 35% under the photovoltaic mode of device operation. A spin dependent tunneling conductance associated with spin polarized electron transport was identified by the observation of phase changes. This transport prevails over the unpolarized electron and hole conduction over the bias range which corresponds to flat band conditions.
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Affiliation(s)
- Y J Park
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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36
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Moodera JS, Kim TH, Tanaka C, De Groot CH. Spin-polarized tunnelling, magnetoresistance and interfacial effects in ferromagnetic junctions. ACTA ACUST UNITED AC 2009. [DOI: 10.1080/13642810008208608] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Jagadeesh S. Moodera
- a Francis Bitter Magnet Laboratory , Massachusetts Institute of Technology , Cambridge , Massachusetts , 02139 , USA
| | - Tae Hee Kim
- a Francis Bitter Magnet Laboratory , Massachusetts Institute of Technology , Cambridge , Massachusetts , 02139 , USA
| | - Clifford Tanaka
- a Francis Bitter Magnet Laboratory , Massachusetts Institute of Technology , Cambridge , Massachusetts , 02139 , USA
| | - Cornelis H. De Groot
- a Francis Bitter Magnet Laboratory , Massachusetts Institute of Technology , Cambridge , Massachusetts , 02139 , USA
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37
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Mohite AD, Santos TS, Moodera JS, Alphenaar BW. Observation of the triplet exciton in EuS-coated single-walled nanotubes. Nat Nanotechnol 2009; 4:425-429. [PMID: 19581894 DOI: 10.1038/nnano.2009.122] [Citation(s) in RCA: 9] [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] [Received: 01/23/2009] [Accepted: 04/28/2009] [Indexed: 05/28/2023]
Abstract
Photon absorption by carbon nanotubes creates bound electron-hole pairs called excitons, which can exist in spin-polarized triplet or spin-unpolarized singlet configurations. Triplet excitons are optically inactive owing to the weak spin-orbit coupling in nanotubes. This prevents the optical injection of electron spin into nanotubes for spintronic applications and limits the efficiency of photocurrent generation. Here, we show that it is possible to optically excite the triplet exciton by using a ferromagnetic semiconductor as a spin filter to mix the singlet and triplet excitons. The triplet contribution to the photocurrent is detected, representing the first direct evidence of the triplet exciton in carbon nanotubes.
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Affiliation(s)
- Aditya D Mohite
- Department of Electrical and Computer Engineering, University of Louisville, Louisville, Kentucky 40292, USA
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Abstract
The damping of magnetization, represented by the rate at which it relaxes to equilibrium, is successfully modeled as a phenomenological extension in the Landau-Lifschitz-Gilbert equation. This is the damping torque term known as Gilbert damping and its direction is given by the vector product of the magnetization and its time derivative. Here we derive the Gilbert term from first-principles by a nonrelativistic expansion of the Dirac equation. We find that this term arises when one calculates the time evolution of the spin observable in the presence of the full spin-orbital coupling terms, while recognizing the relationship between the curl of the electric field and the time-varying magnetic induction.
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Affiliation(s)
- M C Hickey
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, 150 Albany Street, Cambridge, Massachusetts 02139, USA.
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39
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Miao GX, Müller M, Moodera JS. Magnetoresistance in double spin filter tunnel junctions with nonmagnetic electrodes and its unconventional bias dependence. Phys Rev Lett 2009; 102:076601. [PMID: 19257701 DOI: 10.1103/physrevlett.102.076601] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2008] [Indexed: 05/27/2023]
Abstract
Spin filtering happens due to the discriminative tunneling probabilities for spin-up and spin-down electrons through a magnetic barrier and can result in highly spin polarized tunnel currents. Combining two such barriers in a tunnel junction thus leads to large magnetoresistance without the necessity of magnetic electrodes. We demonstrate the realization of such unconventional tunnel junctions using double EuS spin filter barriers with Al electrodes. The novel nonmonotonic and asymmetric bias behavior in magnetoresistance can be qualitatively modeled in the framework of WKB approximations.
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Affiliation(s)
- Guo-Xing Miao
- Francis Bitter Magnet Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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40
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Müller GM, Walowski J, Djordjevic M, Miao GX, Gupta A, Ramos AV, Gehrke K, Moshnyaga V, Samwer K, Schmalhorst J, Thomas A, Hütten A, Reiss G, Moodera JS, Münzenberg M. Spin polarization in half-metals probed by femtosecond spin excitation. Nat Mater 2009; 8:56-61. [PMID: 19079243 DOI: 10.1038/nmat2341] [Citation(s) in RCA: 25] [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: 01/30/2008] [Accepted: 10/21/2008] [Indexed: 05/27/2023]
Abstract
Knowledge of the spin polarization is of fundamental importance for the use of a material in spintronics applications. Here, we used femtosecond optical excitation of half-metals to distinguish between half-metallic and metallic properties. Because the direct energy transfer by Elliot-Yafet scattering is blocked in a half-metal, the demagnetization time is a measure for the degree of half-metallicity. We propose that this characteristic enables us vice versa to establish a novel and fast characterization tool for this highly important material class used in spin-electronic devices. The technique has been applied to a variety of materials where the spin polarization at the Fermi level ranges from 45 to 98%: Ni, Co(2)MnSi, Fe(3)O(4), La(0.66)Sr(0.33)MnO(3) and CrO(2).
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Affiliation(s)
- Georg M Müller
- IV. Phys. Institut, Universität Göttingen, D-37077 Göttingen, Germany
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41
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Santos TS, Moodera JS, Raman KV, Negusse E, Holroyd J, Dvorak J, Liberati M, Idzerda YU, Arenholz E. Determining exchange splitting in a magnetic semiconductor by spin-filter tunneling. Phys Rev Lett 2008; 101:147201. [PMID: 18851564 DOI: 10.1103/physrevlett.101.147201] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Indexed: 05/26/2023]
Abstract
A large exchange splitting of the conduction band in ultrathin films of the ferromagnetic semiconductor EuO was determined quantitatively, by using EuO as a tunnel barrier and fitting the current-voltage characteristics and temperature dependence to tunneling theory. This exchange splitting leads to different tunnel barrier heights for spin-up and spin-down electrons and is large enough to produce a near-fully spin-polarized current. Moreover, the magnetic properties of these ultrathin films (<6 nm) show a reduction in Curie temperature with decreasing thickness, in agreement with theoretical calculation [R. Schiller, Phys. Rev. Lett. 86, 3847 (2001)10.1103/Phys. Rev. Lett.86.3847].
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Affiliation(s)
- T S Santos
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Miao GX, Ramos AV, Moodera JS. Infinite magnetoresistance from the spin dependent proximity effect in symmetry driven bcc-Fe/V/Fe heteroepitaxial superconducting spin valves. Phys Rev Lett 2008; 101:137001. [PMID: 18851482 DOI: 10.1103/physrevlett.101.137001] [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: 06/13/2008] [Indexed: 05/26/2023]
Abstract
Superconductivity in fully epitaxial bcc-Fe/V/Fe hybrid spin valve structures is influenced by the spin currents and supercurrents as well as band symmetry. The transition temperature is spin dependent in the presence of the proximity effect. A unique feature in this system is the band symmetry filtering taking place at the Fe/V interface. The absence of Delta2 Bloch states at the Fermi level in the Fe spin majority channel leads to spin selectivity and reduced transparency at the interface. Infinite magnetoresistance with clear remanence states is obtained, and implies the potential for spintronic applications.
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Affiliation(s)
- Guo-Xing Miao
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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Miao GX, Park YJ, Moodera JS, Seibt M, Eilers G, Münzenberg M. Disturbance of tunneling coherence by oxygen vacancy in epitaxial Fe/MgO/Fe magnetic tunnel junctions. Phys Rev Lett 2008; 100:246803. [PMID: 18643609 DOI: 10.1103/physrevlett.100.246803] [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: 04/04/2008] [Indexed: 05/26/2023]
Abstract
Oxygen vacancies in the MgO barriers of epitaxial Fe/MgO/Fe magnetic tunnel junctions are observed to introduce symmetry-breaking scatterings and hence open up channels for noncoherent tunneling processes that follow the normal WKB approximation. The evanescent waves inside the MgO barrier thus experience two-step tunneling, the coherent followed by the noncoherent process, and lead to lower tunnel magnetoresistance, higher junction resistance, as well as increased bias and temperature dependence. The characteristic length of the symmetry scattering process is determined to be about 1.6 nm.
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Affiliation(s)
- G X Miao
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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Shim JH, Raman KV, Park YJ, Santos TS, Miao GX, Satpati B, Moodera JS. Large spin diffusion length in an amorphous organic semiconductor. Phys Rev Lett 2008; 100:226603. [PMID: 18643439 DOI: 10.1103/physrevlett.100.226603] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2008] [Indexed: 05/26/2023]
Abstract
We directly measured a spin diffusion length (lambdas) of 13.3 nm in amorphous organic semiconductor (OS) rubrene (C42H28) by spin polarized tunneling. In comparison, no spin-conserved transport has been reported in amorphous Si or Ge. Absence of dangling bond defects can explain the spin transport behavior in amorphous OS. Furthermore, when rubrene barriers were grown on a seed layer, the elastic tunneling characteristics were greatly enhanced. Based on our findings, lambdas in single-crystalline rubrene can be expected to reach even millimeters, showing the potential for organic spintronics development.
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Affiliation(s)
- J H Shim
- Francis Bitter Magnet Laboratory, MIT, Cambridge, Massachusetts 02139, USA
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Nagahama T, Santos TS, Moodera JS. Enhanced magnetotransport at high bias in quasimagnetic tunnel junctions with EuS spin-filter barriers. Phys Rev Lett 2007; 99:016602. [PMID: 17678177 DOI: 10.1103/physrevlett.99.016602] [Citation(s) in RCA: 10] [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] [Received: 03/06/2007] [Indexed: 05/16/2023]
Abstract
In quasimagnetic tunnel junctions with a EuS spin-filter tunnel barrier between Al and Co electrodes, we observed large magnetoresistance (MR). The bias dependence shows an abrupt increase of MR ratio in high bias voltage, which is contrary to conventional magnetic tunnel junctions. This behavior can be understood as due to Fowler-Nordheim tunneling through the fully spin-polarized EuS conduction band. The I-V characteristics and bias dependence of MR calculated using tunneling theory show excellent agreement with experiment.
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Affiliation(s)
- T Nagahama
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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46
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Miao GX, Yoon K, Santos TS, Moodera JS. Influence of spin-polarized current on superconductivity and the realization of large magnetoresistance. Phys Rev Lett 2007; 98:267001. [PMID: 17678118 DOI: 10.1103/physrevlett.98.267001] [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: 11/10/2006] [Indexed: 05/16/2023]
Abstract
The superconducting state can be influenced by injecting spin-polarized current in a controlled manner by properly tailoring the interfacial transmittivity between a ferromagnet (F) and a superconductor (S), resulting in a large magnetoresistance of over 1100% for a F/I/S/I/F multilayer system (I insulator). Because of the competition between ferromagnetism and superconductivity, the superconducting transition temperature (T(C)) in the spin-parallel configuration is shifted below that in the spin antiparallel configuration. The T(C) shift is attributed to ferromagnet-induced nonequilibrium spin carriers in the superconductors.
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Affiliation(s)
- Guo-Xing Miao
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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47
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Santos TS, Lee JS, Migdal P, Lekshmi IC, Satpati B, Moodera JS. Room-temperature tunnel magnetoresistance and spin-polarized tunneling through an organic semiconductor barrier. Phys Rev Lett 2007; 98:016601. [PMID: 17358495 DOI: 10.1103/physrevlett.98.016601] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2006] [Indexed: 05/14/2023]
Abstract
Electron spin-polarized tunneling is observed through an ultrathin layer of the molecular organic semiconductor tris(8-hydroxyquinolinato)aluminum (Alq3). Significant tunnel magnetoresistance (TMR) was measured in a Co/Al2O3/Alq3/NiFe magnetic tunnel junction at room temperature, which increased when cooled to low temperatures. Tunneling characteristics, such as the current-voltage behavior and temperature and bias dependence of the TMR, show the good quality of the organic tunnel barrier. Spin polarization (P) of the tunnel current through the Alq3 layer, directly measured using superconducting Al as the spin detector, shows that minimizing formation of an interfacial dipole layer between the metal electrode and organic barrier significantly improves spin transport.
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Affiliation(s)
- T S Santos
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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48
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Guerrero R, Aliev FG, Tserkovnyak Y, Santos TS, Moodera JS. Shot noise in magnetic tunnel junctions: evidence for sequential tunneling. Phys Rev Lett 2006; 97:266602. [PMID: 17280445 DOI: 10.1103/physrevlett.97.266602] [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: 02/21/2006] [Indexed: 05/13/2023]
Abstract
We report the experimental observation of sub-Poissonian shot noise in single magnetic tunnel junctions, indicating the importance of tunneling via impurity levels inside the tunnel barrier. For junctions with weak zero-bias anomaly in conductance, the Fano factor (normalized shot noise) depends on the magnetic configuration being enhanced for antiparallel alignment of the ferromagnetic electrodes. We propose a model of sequential tunneling through nonmagnetic and paramagnetic impurity levels inside the tunnel barrier to qualitatively explain the observations.
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Affiliation(s)
- R Guerrero
- Departamento de Fisica de la Materia Condensada, C-III, Universidad Autonoma de Madrid, 28049 Madrid, Spain
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Philip J, Punnoose A, Kim BI, Reddy KM, Layne S, Holmes JO, Satpati B, Leclair PR, Santos TS, Moodera JS. Carrier-controlled ferromagnetism in transparent oxide semiconductors. Nat Mater 2006; 5:298-304. [PMID: 16547517 DOI: 10.1038/nmat1613] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2005] [Accepted: 01/24/2006] [Indexed: 05/07/2023]
Abstract
The search for an ideal magnetic semiconductor with tunable ferromagnetic behaviour over a wide range of doping or by electrical gating is being actively pursued as a major step towards realizing spin electronics. A magnetic semiconductor having a high Curie temperature, capable of independently controlled carrier density and magnetic doping, is crucial for developing spin-based multifunctional devices. Cr-doped In(2)O(3) is such a unique system, where the electrical and magnetic behaviour-from ferromagnetic metal-like to ferromagnetic semiconducting to paramagnetic insulator-can be controllably tuned by the defect concentration. An explicit dependence of magnetic interaction leading to ferromagnetism on the carrier density is shown. A carrier-density-dependent high Curie temperature of 850-930 K has been measured, in addition to the observation of clear magnetic domain structures in these films. Being optically transparent with the above optimal properties, Cr-doped In(2)O(3) emerges as a viable candidate for the development of spin electronics.
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Affiliation(s)
- J Philip
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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LeClair P, Moodera JS, Philip J, Heiman D. Coexistence of ferromagnetism and superconductivity in Ni/Bi bilayers. Phys Rev Lett 2005; 94:037006. [PMID: 15698312 DOI: 10.1103/physrevlett.94.037006] [Citation(s) in RCA: 6] [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] [Received: 08/09/2004] [Indexed: 05/24/2023]
Abstract
In spite of a lack of superconductivity in bulk crystalline Bi, thin film Bi deposited on thin Ni underlayers are strong-coupled superconductors below approximately 4 K. We unambiguously demonstrate that by tuning the Ni thickness the competition between ferromagnetism and superconductivity in the Ni/Bi can be tailored. For a narrow range of Ni thicknesses, the coexistence of both a superconducting energy gap and conduction electron spin polarization are visible within the Ni side of the Ni/Bi bilayers, independent of any particular theoretical model. We believe that this represents one of the clearest observations of superconductivity and ferromagnetism coexisting.
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Affiliation(s)
- P LeClair
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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