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Mæland K, Sudbø A. Topological Superconductivity Mediated by Skyrmionic Magnons. PHYSICAL REVIEW LETTERS 2023; 130:156002. [PMID: 37115864 DOI: 10.1103/physrevlett.130.156002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 01/23/2023] [Accepted: 02/23/2023] [Indexed: 06/19/2023]
Abstract
Topological superconductors are associated with the appearance of Majorana bound states, with promising applications in topologically protected quantum computing. In this Letter, we study a system where a skyrmion crystal is interfaced with a normal metal. Through interfacial exchange coupling, spin fluctuations in the skyrmion crystal mediate an effective electron-electron interaction in the normal metal. We study superconductivity within a weak-coupling approach and solve gap equations both close to the critical temperature and at zero temperature. Special features in the effective electron-electron interaction due to the noncolinearity of the magnetic ground state yield topological superconductivity at the interface.
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Affiliation(s)
- Kristian Mæland
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Asle Sudbø
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
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Aftergood J, Takei S. Conductivity Enhancement in a Diffusive Fermi Liquid due to Bose-Einstein Condensation of Magnons. PHYSICAL REVIEW LETTERS 2023; 130:086702. [PMID: 36898110 DOI: 10.1103/physrevlett.130.086702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 08/18/2022] [Accepted: 01/20/2023] [Indexed: 06/18/2023]
Abstract
We theoretically study the conductivity of a disordered 2D metal when it is coupled to ferromagnetic magnons with a quadratic spectrum and a gap Δ. In the diffusive limit, a combination of disorder and magnon-mediated electron interaction leads to a sharp metallic correction to the Drude conductivity as the magnons approach criticality, i.e., Δ→0. The correction is nonsingular and is distinctively weaker than, for example, the log-squared correction obtained when disordered electrons couple to diffusive spin fluctuations near a Hertz-Millis transition. The possibility of verifying this prediction in an S=1/2 easy-plane ferromagnetic insulator K_{2}CuF_{4} under an external magnetic field is proposed. Our results show that the onset of a magnon Bose-Einstein condensation in an insulator can be detected via electrical transport measurements on the proximate metal.
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Affiliation(s)
- Joshua Aftergood
- Department of Physics, Queens College of the City University of New York, Queens, New York 11367, USA
- The Graduate Center of the City University of New York, New York, New York 10016, USA
- Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - So Takei
- Department of Physics, Queens College of the City University of New York, Queens, New York 11367, USA
- The Graduate Center of the City University of New York, New York, New York 10016, USA
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Bhattacharyya S, Akhgar G, Gebert M, Karel J, Edmonds MT, Fuhrer MS. Recent Progress in Proximity Coupling of Magnetism to Topological Insulators. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2007795. [PMID: 34185344 DOI: 10.1002/adma.202007795] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 01/11/2021] [Indexed: 05/08/2023]
Abstract
Inducing long-range magnetic order in 3D topological insulators can gap the Dirac-like metallic surface states, leading to exotic new phases such as the quantum anomalous Hall effect or the axion insulator state. These magnetic topological phases can host robust, dissipationless charge and spin currents or unique magnetoelectric behavior, which can be exploited in low-energy electronics and spintronics applications. Although several different strategies have been successfully implemented to realize these states, to date these phenomena have been confined to temperatures below a few Kelvin. This review focuses on one strategy: inducing magnetic order in topological insulators by proximity of magnetic materials, which has the capability for room temperature operation, unlocking the potential of magnetic topological phases for applications. The unique advantages of this strategy, the important physical mechanisms facilitating magnetic proximity effect, and the recent progress to achieve, understand, and harness proximity-coupled magnetic order in topological insulators are discussed. Some emerging new phenomena and applications enabled by proximity coupling of magnetism and topological materials, such as skyrmions and the topological Hall effect, are also highlighted, and the authors conclude with an outlook on remaining challenges and opportunities in the field.
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Affiliation(s)
- Semonti Bhattacharyya
- School of Physics and Astronomy, Monash University, Victoria, 3800, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Victoria, 3800, Australia
| | - Golrokh Akhgar
- School of Physics and Astronomy, Monash University, Victoria, 3800, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Victoria, 3800, Australia
| | - Matthew Gebert
- School of Physics and Astronomy, Monash University, Victoria, 3800, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Victoria, 3800, Australia
| | - Julie Karel
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Victoria, 3800, Australia
- Department of Materials Science and Engineering, Monash University, Clayton, Victoria, 3800, Australia
| | - Mark T Edmonds
- School of Physics and Astronomy, Monash University, Victoria, 3800, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Victoria, 3800, Australia
| | - Michael S Fuhrer
- School of Physics and Astronomy, Monash University, Victoria, 3800, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Victoria, 3800, Australia
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Johansen Ø, Kamra A, Ulloa C, Brataas A, Duine RA. Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators. PHYSICAL REVIEW LETTERS 2019; 123:167203. [PMID: 31702374 DOI: 10.1103/physrevlett.123.167203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Indexed: 06/10/2023]
Abstract
Electrons and holes residing on the opposing sides of an insulating barrier and experiencing an attractive Coulomb interaction can spontaneously form a coherent state known as an indirect exciton condensate. We study a trilayer system where the barrier is an antiferromagnetic insulator. The electrons and holes here additionally interact via interfacial coupling to the antiferromagnetic magnons. We show that by employing magnetically uncompensated interfaces, we can design the magnon-mediated interaction to be attractive or repulsive by varying the thickness of the antiferromagnetic insulator by a single atomic layer. We derive an analytical expression for the critical temperature T_{c} of the indirect exciton condensation. Within our model, anisotropy is found to be crucial for achieving a finite T_{c}, which increases with the strength of the exchange interaction in the antiferromagnetic bulk. For realistic material parameters, we estimate T_{c} to be around 7 K, the same order of magnitude as the current experimentally achievable exciton condensation where the attraction is solely due to the Coulomb interaction. The magnon-mediated interaction is expected to cooperate with the Coulomb interaction for condensation of indirect excitons, thereby providing a means to significantly increase the exciton condensation temperature range.
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Affiliation(s)
- Øyvind Johansen
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Akashdeep Kamra
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Camilo Ulloa
- Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584CC Utrecht, Netherlands
| | - Arne Brataas
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Rembert A Duine
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
- Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584CC Utrecht, Netherlands
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven, Netherlands
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Schlawin F, Cavalleri A, Jaksch D. Cavity-Mediated Electron-Photon Superconductivity. PHYSICAL REVIEW LETTERS 2019; 122:133602. [PMID: 31012600 DOI: 10.1103/physrevlett.122.133602] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2018] [Revised: 02/06/2019] [Indexed: 05/03/2023]
Abstract
We investigate electron paring in a two-dimensional electron system mediated by vacuum fluctuations inside a nanoplasmonic terahertz cavity. We show that the structured cavity vacuum can induce long-range attractive interactions between current fluctuations which lead to pairing in generic materials with critical temperatures in the low-kelvin regime for realistic parameters. The induced state is a pair-density wave superconductor which can show a transition from a fully gapped to a partially gapped phase-akin to the pseudogap phase in high-T_{c} superconductors. Our findings provide a promising tool for engineering intrinsic electron interactions in two-dimensional materials.
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Affiliation(s)
- Frank Schlawin
- Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - Andrea Cavalleri
- Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Dieter Jaksch
- Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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Gotlieb K, Lin CY, Serbyn M, Zhang W, Smallwood CL, Jozwiak C, Eisaki H, Hussain Z, Vishwanath A, Lanzara A. Revealing hidden spin-momentum locking in a high-temperature cuprate superconductor. Science 2018; 362:1271-1275. [PMID: 30545882 DOI: 10.1126/science.aao0980] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Revised: 02/24/2018] [Accepted: 11/07/2018] [Indexed: 11/02/2022]
Abstract
Cuprate superconductors have long been thought of as having strong electronic correlations but negligible spin-orbit coupling. Using spin- and angle-resolved photoemission spectroscopy, we discovered that one of the most studied cuprate superconductors, Bi2212, has a nontrivial spin texture with a spin-momentum locking that circles the Brillouin zone center and a spin-layer locking that allows states of opposite spin to be localized in different parts of the unit cell. Our findings pose challenges for the vast majority of models of cuprates, such as the Hubbard model and its variants, where spin-orbit interaction has been mostly neglected, and open the intriguing question of how the high-temperature superconducting state emerges in the presence of this nontrivial spin texture.
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Affiliation(s)
- Kenneth Gotlieb
- Graduate Group in Applied Science and Technology, University of California, Berkeley, CA 94720, USA.,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Chiu-Yun Lin
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.,Department of Physics, University of California, Berkeley, CA 94720, USA
| | - Maksym Serbyn
- Institute of Science and Technology Austria, 3400 Klosterneuburg, Austria
| | - Wentao Zhang
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.,School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Christopher L Smallwood
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.,Department of Physics, University of California, Berkeley, CA 94720, USA
| | - Christopher Jozwiak
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Hiroshi Eisaki
- Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan
| | - Zahid Hussain
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | | | - Alessandra Lanzara
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. .,Department of Physics, University of California, Berkeley, CA 94720, USA
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Gong X, Kargarian M, Stern A, Yue D, Zhou H, Jin X, Galitski VM, Yakovenko VM, Xia J. Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers. SCIENCE ADVANCES 2017; 3:e1602579. [PMID: 28435865 PMCID: PMC5375641 DOI: 10.1126/sciadv.1602579] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Accepted: 02/10/2017] [Indexed: 05/14/2023]
Abstract
Superconductivity that spontaneously breaks time-reversal symmetry (TRS) has been found, so far, only in a handful of three-dimensional (3D) crystals with bulk inversion symmetry. We report an observation of spontaneous TRS breaking in a 2D superconducting system without inversion symmetry: the epitaxial bilayer films of bismuth and nickel. The evidence comes from the onset of the polar Kerr effect at the superconducting transition in the absence of an external magnetic field, detected by the ultrasensitive loop-less fiber-optic Sagnac interferometer. Because of strong spin-orbit interaction and lack of inversion symmetry in a Bi/Ni bilayer, superconducting pairing cannot be classified as singlet or triplet. We propose a theoretical model where magnetic fluctuations in Ni induce the superconducting pairing of the [Formula: see text] orbital symmetry between the electrons in Bi. In this model, the order parameter spontaneously breaks the TRS and has a nonzero phase winding number around the Fermi surface, thus making it a rare example of a 2D topological superconductor.
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Affiliation(s)
- Xinxin Gong
- Department of Physics and Astronomy, University of California, Irvine, Irvine, CA 92697, USA
- Department of Physics, Fudan University, Shanghai 200433, China
| | - Mehdi Kargarian
- Department of Physics, Condensed Matter Theory Center and Joint Quantum Institute, University of Maryland, College Park, MD 20742, USA
| | - Alex Stern
- Department of Physics and Astronomy, University of California, Irvine, Irvine, CA 92697, USA
| | - Di Yue
- Department of Physics, Fudan University, Shanghai 200433, China
| | - Hexin Zhou
- Department of Physics, Fudan University, Shanghai 200433, China
| | - Xiaofeng Jin
- Department of Physics, Fudan University, Shanghai 200433, China
| | - Victor M. Galitski
- Department of Physics, Condensed Matter Theory Center and Joint Quantum Institute, University of Maryland, College Park, MD 20742, USA
| | - Victor M. Yakovenko
- Department of Physics, Condensed Matter Theory Center and Joint Quantum Institute, University of Maryland, College Park, MD 20742, USA
| | - Jing Xia
- Department of Physics and Astronomy, University of California, Irvine, Irvine, CA 92697, USA
- Corresponding author.
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