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Wu H, Sauls JA. Weyl Fermions and broken symmetry phases of laterally confined 3He films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:495402. [PMID: 37625425 DOI: 10.1088/1361-648x/acf42b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2023] [Accepted: 08/25/2023] [Indexed: 08/27/2023]
Abstract
Broken symmetries in topological condensed matter systems have implications for the spectrum of Fermionic excitations confined on surfaces or topological defects. The Fermionic spectrum of confined (quasi-2D)3He-A consists of branches of chiral edge states. The negative energy states are related to the ground-state angular momentum,Lz=(N/2)ℏ, forN/2Cooper pairs. The power law suppression of the angular momentum,Lz(T)≃(N/2)ℏ[1-23(πT/Δ)2]for0⩽T≪Tc, in the fully gapped 2D chiral A-phase reflects the thermal excitation of the chiral edge Fermions. We discuss the effects of wave function overlap, and hybridization between edge states confined near opposing edge boundaries on the edge currents, ground-state angular momentum and ground-state order parameter of superfluid3He thin films. Under strong lateral confinement, the chiral A phase undergoes a sequence of phase transitions, first to a pair density wave (PDW) phase with broken translational symmetry atDc2∼16ξ0. The PDW phase is described by a periodic array of chiral domains with alternating chirality, separated by domain walls. The period of PDW phase diverges as the confinement lengthD→Dc2. The PDW phase breaks time-reversal symmetry, translation invariance, but is invariant under the combination of time-reversal and translation by a one-half period of the PDW. The mass current distribution of the PDW phase reflects this combined symmetry, and originates from the spectra of edge Fermions and the chiral branches bound to the domain walls. Under sufficiently strong confinement a second-order transition occurs to the non-chiral 'polar phase' atDc1∼9ξ0, in which a single p-wave orbital state of Cooper pairs is aligned along the channel.
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Affiliation(s)
- Hao Wu
- Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, United States of America
| | - J A Sauls
- Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, United States of America
- Hearne Institute of Theoretical Physics, Louisiana State University, Baton Rouge, LA 70803, United States of America
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2
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Yazdani-Hamid M. Effect of nonequilibrium order parameter on the optical response of superconductor Sr 2RuO 4. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:455603. [PMID: 36041424 DOI: 10.1088/1361-648x/ac8dd2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 08/30/2022] [Indexed: 06/15/2023]
Abstract
The breaking of time reversal symmetry of the superconducting pairings is expected to manifest itself through characteristic transport properties such as a non-zero Kerr angle which provides fingerprint of the quantum anomalous Hall state. In this work, we theoretically study the Kerr effect or the Hall-type response and also consider how this response is modified by the nonequilibrium shape of order parameter of the superconducting state due to the influence of the electromagnetic radiation for the most favorable candidates of chiral superconducting order parameters and of the non-chiral states in strontium ruthenate (Sr2RuO4). The unique sensitivity of the Hall-type response introduced above to different types of pairings can be used to identify the most favored pairing which is a serious doubt on the superconducting state of this material.
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Affiliation(s)
- Meghdad Yazdani-Hamid
- Department of Physics, Ayatollah Boroujerdi University, Boroujerd, Lorestan 65151-36111, Iran
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3
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Jerzembeck F, Røising HS, Steppke A, Rosner H, Sokolov DA, Kikugawa N, Scaffidi T, Simon SH, Mackenzie AP, Hicks CW. The superconductivity of Sr 2RuO 4 under c-axis uniaxial stress. Nat Commun 2022; 13:4596. [PMID: 35933412 PMCID: PMC9357014 DOI: 10.1038/s41467-022-32177-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 07/19/2022] [Indexed: 11/15/2022] Open
Abstract
Applying in-plane uniaxial pressure to strongly correlated low-dimensional systems has been shown to tune the electronic structure dramatically. For example, the unconventional superconductor Sr2RuO4 can be tuned through a single Van Hove point, resulting in strong enhancement of both Tc and Hc2. Out-of-plane (c axis) uniaxial pressure is expected to tune the quasi-two-dimensional structure even more strongly, by pushing it towards two Van Hove points simultaneously. Here, we achieve a record uniaxial stress of 3.2 GPa along the c axis of Sr2RuO4. Hc2 increases, as expected for increasing density of states, but unexpectedly Tc falls. As a first attempt to explain this result, we present three-dimensional calculations in the weak interaction limit. We find that within the weak-coupling framework there is no single order parameter that can account for the contrasting effects of in-plane versus c-axis uniaxial stress, which makes this new result a strong constraint on theories of the superconductivity of Sr2RuO4. In the superconductor Sr2RuO4, in-plane strain is known to enhance both the superconducting transition temperature Tc and upper critical field Hc2, but the effect of out-of-plane strain has not been studied. Here, the authors find that Hc2 is enhanced under out-of-plane strain, but Tc unexpectedly decreases.
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Affiliation(s)
- Fabian Jerzembeck
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str 40, 01187, Dresden, Germany.
| | - Henrik S Røising
- Nordita, KTH Royal Institute of Technology and Stockholm University, Hannes Alfvéns väg 12, SE-106 91, Stockholm, Sweden
| | - Alexander Steppke
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str 40, 01187, Dresden, Germany
| | - Helge Rosner
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str 40, 01187, Dresden, Germany
| | - Dmitry A Sokolov
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str 40, 01187, Dresden, Germany
| | - Naoki Kikugawa
- National Institute for Materials Science, Tsukuba, 305-0003, Japan
| | - Thomas Scaffidi
- Department of Physics, University of Toronto, Toronto, ON, M5S 1A7, Canada.,Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA
| | - Steven H Simon
- Rudolf Peierls Center for Theoretical Physics, Oxford, OX1 3PU, UK
| | - Andrew P Mackenzie
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str 40, 01187, Dresden, Germany. .,Scottish Universities Physics Alliance, School of Physics and Astronomy, University of St. Andrews, St. Andrews, KY16 9SS, UK.
| | - Clifford W Hicks
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str 40, 01187, Dresden, Germany. .,School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK.
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Li YS, Kikugawa N, Sokolov DA, Jerzembeck F, Gibbs AS, Maeno Y, Hicks CW, Schmalian J, Nicklas M, Mackenzie AP. High-sensitivity heat-capacity measurements on Sr 2RuO 4 under uniaxial pressure. Proc Natl Acad Sci U S A 2021; 118:e2020492118. [PMID: 33653958 PMCID: PMC7958258 DOI: 10.1073/pnas.2020492118] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 01/13/2021] [Indexed: 11/18/2022] Open
Abstract
A key question regarding the unconventional superconductivity of [Formula: see text] remains whether the order parameter is single- or two-component. Under a hypothesis of two-component superconductivity, uniaxial pressure is expected to lift their degeneracy, resulting in a split transition. The most direct and fundamental probe of a split transition is heat capacity. Here, we report measurement of heat capacity of samples subject to large and highly homogeneous uniaxial pressure. We place an upper limit on the heat-capacity signature of any second transition of a few percent of that of the primary superconducting transition. The normalized jump in heat capacity, [Formula: see text], grows smoothly as a function of uniaxial pressure, favoring order parameters which are allowed to maximize in the same part of the Brillouin zone as the well-studied van Hove singularity. Thanks to the high precision of our measurements, these findings place stringent constraints on theories of the superconductivity of [Formula: see text].
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Affiliation(s)
- You-Sheng Li
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, United Kingdom
| | - Naoki Kikugawa
- National Institute for Materials Science, Tsukuba 305-0003, Japan
| | - Dmitry A Sokolov
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Fabian Jerzembeck
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Alexandra S Gibbs
- ISIS Facility, Science and Technology Facilities Council Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom
| | - Yoshiteru Maeno
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Clifford W Hicks
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Jörg Schmalian
- Institut für Theorie der Kondensierten Materie, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
- Institut für Quantenmaterialien und Technologien, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
| | - Michael Nicklas
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany;
| | - Andrew P Mackenzie
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany;
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, United Kingdom
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5
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Momentum-resolved superconducting energy gaps of Sr 2RuO 4 from quasiparticle interference imaging. Proc Natl Acad Sci U S A 2020; 117:5222-5227. [PMID: 32094178 DOI: 10.1073/pnas.1916463117] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Sr2RuO4 has long been the focus of intense research interest because of conjectures that it is a correlated topological superconductor. It is the momentum space (k-space) structure of the superconducting energy gap [Formula: see text] on each band i that encodes its unknown superconducting order parameter. However, because the energy scales are so low, it has never been possible to directly measure the [Formula: see text] of Sr2RuO4 Here, we implement Bogoliubov quasiparticle interference (BQPI) imaging, a technique capable of high-precision measurement of multiband [Formula: see text] At T = 90 mK, we visualize a set of Bogoliubov scattering interference wavevectors [Formula: see text] consistent with eight gap nodes/minima that are all closely aligned to the [Formula: see text] crystal lattice directions on both the α and β bands. Taking these observations in combination with other very recent advances in directional thermal conductivity [E. Hassinger et al., Phys. Rev. X 7, 011032 (2017)], temperature-dependent Knight shift [A. Pustogow et al., Nature 574, 72-75 (2019)], time-reversal symmetry conservation [S. Kashiwaya et al., Phys. Rev B, 100, 094530 (2019)], and theory [A. T. Rømer et al., Phys. Rev. Lett. 123, 247001 (2019); H. S. Roising, T. Scaffidi, F. Flicker, G. F. Lange, S. H. Simon, Phys. Rev. Res. 1, 033108 (2019); and O. Gingras, R. Nourafkan, A. S. Tremblay, M. Côté, Phys. Rev. Lett. 123, 217005 (2019)], the BQPI signature of Sr2RuO4 appears most consistent with [Formula: see text] having [Formula: see text] [Formula: see text] symmetry.
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Gingras O, Nourafkan R, Tremblay AMS, Côté M. Superconducting Symmetries of Sr_{2}RuO_{4} from First-Principles Electronic Structure. PHYSICAL REVIEW LETTERS 2019; 123:217005. [PMID: 31809152 DOI: 10.1103/physrevlett.123.217005] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Indexed: 06/10/2023]
Abstract
Although correlated electronic-structure calculations explain very well the normal state of Sr_{2}RuO_{4}, its superconducting symmetry is still unknown. Here we construct the spin and charge fluctuation pairing interactions based on its correlated normal state. Correlations significantly reduce ferromagnetic in favor of antiferromagnetic fluctuations and increase interorbital pairing. From the normal-state Eliashberg equations, we find spin-singlet d-wave pairing close to magnetic instabilities. Away from these instabilities, where charge fluctuations increase, we find two time-reversal symmetry-breaking spin triplets: an odd-frequency s wave, and a doubly degenerate interorbital pairing between d_{xy} and (d_{yz},d_{xz}).
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Affiliation(s)
- O Gingras
- Département de Physique and Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C. P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada
| | - R Nourafkan
- Département de Physique, Institut quantique, Regroupement Québécois sur les Matériaux de Pointe, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada
| | - A-M S Tremblay
- Département de Physique, Institut quantique, Regroupement Québécois sur les Matériaux de Pointe, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada
- Canadian Institute for Advanced Research, Toronto, Ontario, Canada M5G 1Z8
| | - M Côté
- Département de Physique and Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C. P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada
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Abstract
Recent work done on the time reversal symmetry (TRS) breaking superconductors is reviewed in this paper. The special attention is paid to Sr 2 RuO 4 believed to be spin triplet chiral p-wave superconductor which break TRS and is expected to posses non-trivial topological properties. The family of TRS breaking superconductors is growing relatively fast, with many of its newly discovered members being non-centrosymmetric. However not only Sr 2 RuO 4 but also many other superconductors which possess center of inversion also break TRS. The TRS is often identified by means of the muon spin relaxation ( μ SR) and the Kerr effect. Both methods effectively measure the appearance of the spontaneous bulk magnetic field below superconducting transition temperature. This compound provides an example of the material whose many band, multi-condensate modeling has enjoyed a number of successes, but the full understanding has not been achieved yet. We discuss in some details the properties of the material. Among them is the Kerr effect and by understanding has resulted in the discovery of the novel mechanism of the phenomenon. The mechanism is universal and thus applicable to all systems with multi-orbital character of states at the Fermi energy.
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8
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Steffens P, Sidis Y, Kulda J, Mao ZQ, Maeno Y, Mazin II, Braden M. Spin Fluctuations in Sr_{2}RuO_{4} from Polarized Neutron Scattering: Implications for Superconductivity. PHYSICAL REVIEW LETTERS 2019; 122:047004. [PMID: 30768293 DOI: 10.1103/physrevlett.122.047004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Indexed: 06/09/2023]
Abstract
Triplet pairing in Sr_{2}RuO_{4} was initially suggested based on the hypothesis of strong ferromagnetic spin fluctuations. Using polarized inelastic neutron scattering, we accurately determine the full spectrum of spin fluctuations in Sr_{2}RuO_{4}. Besides the well-studied incommensurate magnetic fluctuations, we do find a sizable quasiferromagnetic signal, quantitatively consistent with all macroscopic and microscopic probes. We use this result to address the possibility of magnetically driven triplet superconductivity in Sr_{2}RuO_{4}. We conclude that, even though the quasiferromagnetic signal is stronger and sharper than previously anticipated, spin fluctuations alone are not enough to generate a triplet state strengthening the need for additional interactions or an alternative pairing scenario.
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Affiliation(s)
- P Steffens
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
- Institut Laue Langevin, 71 avenue des Martyrs, 38000 Grenoble, France
| | - Y Sidis
- Laboratoire Léon Brillouin, C.E.A./C.N.R.S., F-91191 Gif-sur-Yvette CEDEX, France
| | - J Kulda
- Institut Laue Langevin, 71 avenue des Martyrs, 38000 Grenoble, France
| | - Z Q Mao
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- Department of Physics, Tulane University, New Orleans, Louisiana 70118, USA
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Y Maeno
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - I I Mazin
- Code 6393, Naval Research Laboratory, Washington, DC 20375, USA
| | - M Braden
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
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9
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Wang WS, Zhang CC, Zhang FC, Wang QH. Theory of Chiral p-Wave Superconductivity with Near Nodes for Sr_{2}RuO_{4}. PHYSICAL REVIEW LETTERS 2019; 122:027002. [PMID: 30720289 DOI: 10.1103/physrevlett.122.027002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2018] [Indexed: 06/09/2023]
Abstract
We use the functional renormalization group method to study a three-orbital model for superconducting Sr_{2}RuO_{4}. Although the pairing symmetry is found to be a chiral p wave, the atomic spin-orbit coupling induces near nodes for quasiparticle excitations. Our theory explains a major experimental puzzle between a d-wavelike feature observed in thermal experiments and the chiral p-wave triplet pairing revealed in nuclear-magnetic resonance and the Kerr effect.
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Affiliation(s)
- Wan-Sheng Wang
- Department of Physics, Ningbo University, Ningbo 315211, China
- National Laboratory of Solid State Microstructures & School of Physics, Nanjing University, Nanjing 210093, China
| | - Cong-Cong Zhang
- Department of Physics, Ningbo University, Ningbo 315211, China
| | - Fu-Chun Zhang
- Kavli Institute for Theoretical Sciences & CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Qiang-Hua Wang
- National Laboratory of Solid State Microstructures & School of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
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10
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Huang W, Yao H. Possible Three-Dimensional Nematic Odd-Parity Superconductivity in Sr_{2}RuO_{4}. PHYSICAL REVIEW LETTERS 2018; 121:157002. [PMID: 30362809 DOI: 10.1103/physrevlett.121.157002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Indexed: 06/08/2023]
Abstract
The superconducting pairing in Sr_{2}RuO_{4} is widely considered to be chiral p wave with d[over →]_{k}∼(k_{x}+ik_{y})z[over ^], which belongs to the E_{u} representation of the crystalline D_{4h} group. However, this superconducting order appears hard to reconcile with a number of key experiments. In this Letter, based on symmetry analysis we discuss the possibility of odd-parity pairing with inherent three-dimensional character enforced by the interorbital interlayer coupling and the sizable spin-orbit coupling in the material. We focus on a yet unexplored E_{u} pairing, which contains finite (k_{z}x[over ^], k_{z}y[over ^]) component in the gap function. Under appropriate circumstances a novel time-reversal invariant nematic pairing can be realized. This nematic superconducting state could make contact with some puzzling observations on Sr_{2}RuO_{4}, such as the absence of spontaneous edge current and no evidence of split transitions under uniaxial strains.
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Affiliation(s)
- Wen Huang
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
| | - Hong Yao
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
- State Key Laboratory of Low Dimensional Quantum Physics, Tsinghua University, Beijing 100084, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
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11
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Komendová L, Black-Schaffer AM. Odd-Frequency Superconductivity in Sr_{2}RuO_{4} Measured by Kerr Rotation. PHYSICAL REVIEW LETTERS 2017; 119:087001. [PMID: 28952759 DOI: 10.1103/physrevlett.119.087001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Indexed: 06/07/2023]
Abstract
We establish the existence of bulk odd-frequency superconductivity in Sr_{2}RuO_{4} and show that an intrinsic Kerr effect is direct evidence of this state. We use both general two- and three-orbital models, as well as a realistic tight-binding description of Sr_{2}RuO_{4} to demonstrate that odd-frequency pairing arises due to finite hybridization between different orbitals in the normal state, and is further enhanced by finite interorbital pairing.
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Affiliation(s)
- L Komendová
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden
| | - A M Black-Schaffer
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden
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12
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Hsu YT, Vaezi A, Fischer MH, Kim EA. Topological superconductivity in monolayer transition metal dichalcogenides. Nat Commun 2017; 8:14985. [PMID: 28397804 PMCID: PMC5394266 DOI: 10.1038/ncomms14985] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Accepted: 02/20/2017] [Indexed: 12/23/2022] Open
Abstract
Theoretically, it has been known that breaking spin degeneracy and effectively realizing spinless fermions is a promising path to topological superconductors. Yet, topological superconductors are rare to date. Here we propose to realize spinless fermions by splitting the spin degeneracy in momentum space. Specifically, we identify monolayer hole-doped transition metal dichalcogenide (TMD)s as candidates for topological superconductors out of such momentum-space-split spinless fermions. Although electron-doped TMDs have recently been found superconducting, the observed superconductivity is unlikely topological because of the near spin degeneracy. Meanwhile, hole-doped TMDs with momentum-space-split spinless fermions remain unexplored. Employing a renormalization group analysis, we propose that the unusual spin-valley locking in hole-doped TMDs together with repulsive interactions selectively favours two topological superconducting states: interpocket paired state with Chern number 2 and intrapocket paired state with finite pair momentum. A confirmation of our predictions will open up possibilities for manipulating topological superconductors on the device-friendly platform of monolayer TMDs.
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Affiliation(s)
- Yi-Ting Hsu
- Department of Physics, Cornell University, Ithaca, New York 14853, USA
| | - Abolhassan Vaezi
- Department of Physics, Stanford University, Stanford, California 94305-4060, USA
| | - Mark H. Fischer
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Eun-Ah Kim
- Department of Physics, Cornell University, Ithaca, New York 14853, USA
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Kunkemöller S, Steffens P, Link P, Sidis Y, Mao ZQ, Maeno Y, Braden M. Absence of a Large Superconductivity-Induced Gap in Magnetic Fluctuations of Sr_{2}RuO_{4}. PHYSICAL REVIEW LETTERS 2017; 118:147002. [PMID: 28430489 DOI: 10.1103/physrevlett.118.147002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Indexed: 06/07/2023]
Abstract
Inelastic neutron scattering experiments on Sr_{2}RuO_{4} determine the spectral weight of the nesting induced magnetic fluctuations across the superconducting transition. There is no observable change at the superconducting transition down to an energy of ∼0.35 meV, which is well below the 2Δ values reported in several tunneling experiments. At this and higher energies magnetic fluctuations clearly persist in the superconducting state. Only at energies below ∼0.3 meV can evidence for partial suppression of spectral weight in the superconducting state be observed. This strongly suggests that the one-dimensional bands with the associated nesting fluctuations do not form the active, highly gapped bands in the superconducting pairing in Sr_{2}RuO_{4}.
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Affiliation(s)
- S Kunkemöller
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany
| | - P Steffens
- Institut Laue Langevin, 71 avenue des Martyrs, 38000 Grenoble, France
| | - P Link
- Heinz Maier-Leibnitz Zentrum, Technische Universität München, Lichtenbergstrasse 1, 85748 Garching, Germany
| | - Y Sidis
- Laboratoire Léon Brillouin, C.E.A./C.N.R.S., F-91191 Gif-sur-Yvette CEDEX, France
| | - Z Q Mao
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- Department of Physics, Tulane University, New Orleans, Louisiana 70118, USA
| | - Y Maeno
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - M Braden
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany
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14
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Acharya S, Laad MS, Dey D, Maitra T, Taraphder A. First-Principles Correlated Approach to the Normal State of Strontium Ruthenate. Sci Rep 2017; 7:43033. [PMID: 28220879 PMCID: PMC5318872 DOI: 10.1038/srep43033] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 01/17/2017] [Indexed: 11/12/2022] Open
Abstract
The interplay between multiple bands, sizable multi-band electronic correlations and strong spin-orbit coupling may conspire in selecting a rather unusual unconventional pairing symmetry in layered Sr2RuO4. This mandates a detailed revisit of the normal state and, in particular, the T-dependent incoherence-coherence crossover. Using a modern first-principles correlated view, we study this issue in the actual structure of Sr2RuO4 and present a unified and quantitative description of a range of unusual physical responses in the normal state. Armed with these, we propose that a new and important element, that of dominant multi-orbital charge fluctuations in a Hund's metal, may be a primary pair glue for unconventional superconductivity. Thereby we establish a connection between the normal state responses and superconductivity in this system.
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Affiliation(s)
- S. Acharya
- Department of Physics, Indian Institute of Technology, Kharagpur, Kharagpur 721302, India
- Physics department, Kings College London, WC2R 2LS, UK
| | - M. S. Laad
- Institute of Mathematical Sciences, Taramani, Chennai 600113, India
- Max-Planck Inst. fuer Physik Komplexer Systeme, 38 Noethnitzer Strasse, 01187 Dresden, Germany
| | - Dibyendu Dey
- Department of Physics, Indian Institute of Technology, Kharagpur, Kharagpur 721302, India
| | - T. Maitra
- Department of Physics, Indian Institute of Technology, Roorkee, Roorkee 247667, India
| | - A. Taraphder
- Department of Physics, Indian Institute of Technology, Kharagpur, Kharagpur 721302, India
- Centre for Theoretical Studies, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
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Two-dimensional chiral topological superconductivity in Shiba lattices. Nat Commun 2016; 7:12297. [PMID: 27465127 PMCID: PMC4974475 DOI: 10.1038/ncomms12297] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Accepted: 06/22/2016] [Indexed: 11/28/2022] Open
Abstract
The chiral p-wave superconductor is the archetypal example of a state of matter that supports non-Abelian anyons, a highly desired type of exotic quasiparticle. With this, it is foundational for the distant goal of building a topological quantum computer. While some candidate materials for bulk chiral superconductors exist, they are subject of an ongoing debate about their actual paring state. Here we propose an alternative route to chiral superconductivity, consisting of the surface of an ordinary superconductor decorated with a two-dimensional lattice of magnetic impurities. We furthermore identify a promising experimental platform to realize this proposal. Chiral p-wave superconductors may form the basis for topological quantum computers however one has yet to be identified. Here, the authors propose that such a state may be created by a two-dimensional array of magnetic adatoms on the surface of a superconductor with strong spin-orbit coupling.
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16
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Burganov B, Adamo C, Mulder A, Uchida M, King PDC, Harter JW, Shai DE, Gibbs AS, Mackenzie AP, Uecker R, Bruetzam M, Beasley MR, Fennie CJ, Schlom DG, Shen KM. Strain Control of Fermiology and Many-Body Interactions in Two-Dimensional Ruthenates. PHYSICAL REVIEW LETTERS 2016; 116:197003. [PMID: 27232037 DOI: 10.1103/physrevlett.116.197003] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Indexed: 06/05/2023]
Abstract
Here we demonstrate how the Fermi surface topology and quantum many-body interactions can be manipulated via epitaxial strain in the spin-triplet superconductor Sr_{2}RuO_{4} and its isoelectronic counterpart Ba_{2}RuO_{4} using oxide molecular beam epitaxy, in situ angle-resolved photoemission spectroscopy, and transport measurements. Near the topological transition of the γ Fermi surface sheet, we observe clear signatures of critical fluctuations, while the quasiparticle mass enhancement is found to increase rapidly and monotonically with increasing Ru-O bond distance. Our work demonstrates the possibilities for using epitaxial strain as a disorder-free means of manipulating emergent properties, many-body interactions, and potentially the superconductivity in correlated materials.
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Affiliation(s)
- B Burganov
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, New York 14853, USA
| | - C Adamo
- Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - A Mulder
- School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
| | - M Uchida
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, New York 14853, USA
| | - P D C King
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, New York 14853, USA
- School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, United Kingdom
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
| | - J W Harter
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, New York 14853, USA
| | - D E Shai
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, New York 14853, USA
| | - A S Gibbs
- Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
| | - A P Mackenzie
- School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, United Kingdom
- Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
| | - R Uecker
- Leibniz Institute for Crystal Growth, D-12489 Berlin, Germany
| | - M Bruetzam
- Leibniz Institute for Crystal Growth, D-12489 Berlin, Germany
| | - M R Beasley
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - C J Fennie
- School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
| | - D G Schlom
- Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
| | - K M Shen
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, New York 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
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17
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Kallin C, Berlinsky J. Chiral superconductors. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2016; 79:054502. [PMID: 27088452 DOI: 10.1088/0034-4885/79/5/054502] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Chiral superconductivity is a striking quantum phenomenon in which an unconventional superconductor spontaneously develops an angular momentum and lowers its free energy by eliminating nodes in the gap. It is a topologically non-trivial state and, as such, exhibits distinctive topological modes at surfaces and defects. In this paper we discuss the current theory and experimental results on chiral superconductors, focusing on two of the best-studied systems, Sr2RuO4, which is thought to be a chiral triplet p-wave superconductor, and UPt3, which has two low-temperature superconducting phases (in zero magnetic field), the lower of which is believed to be chiral triplet f-wave. Other systems that may exhibit chiral superconductivity are also discussed. Key signatures of chiral superconductivity are surface currents and chiral Majorana modes, Majorana states in vortex cores, and the possibility of half-flux quantum vortices in the case of triplet pairing. Experimental evidence for chiral superconductivity from μSR, NMR, strain, polar Kerr effect and Josephson tunneling experiments are discussed.
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18
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Scaffidi T, Simon SH. Large Chern Number and Edge Currents in Sr2RuO4. PHYSICAL REVIEW LETTERS 2015; 115:087003. [PMID: 26340202 DOI: 10.1103/physrevlett.115.087003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Indexed: 06/05/2023]
Abstract
We show from a weak-coupling microscopic calculation that the most favored chiral superconducting order parameter in Sr2RuO4 has a Chern number of |C|=7. The two dominant components of this order parameter are given by sin(3k(x))+isin(3k(y)) and sin(k(x))cos(k(y))+isin(k(y))cos(k(x)) and lie in the same irreducible representation E(u) of the tetragonal point group as the usually assumed gap function, sin(k(x))+isin(k(y)). While the latter gap function leads to C=1, the two former lead to C=-7, which is also allowed for an E_{u} gap function since the tetragonal symmetry only fixes C modulo 4. Since it was shown that the edge currents of a |C|>1 superconductor vanish exactly in the continuum limit, and can be strongly reduced on the lattice, this form of order parameter could help resolve the conflict between experimental observation of time-reversal symmetry breaking and yet the absence of observed edge currents in Sr2RuO4.
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Affiliation(s)
- Thomas Scaffidi
- Rudolf Peierls Centre for Theoretical Physics, Oxford OX1 3NP, United Kingdom
| | - Steven H Simon
- Rudolf Peierls Centre for Theoretical Physics, Oxford OX1 3NP, United Kingdom
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19
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Black-Schaffer AM, Honerkamp C. Chiral d-wave superconductivity in doped graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:423201. [PMID: 25238054 DOI: 10.1088/0953-8984/26/42/423201] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
A highly unconventional superconducting state with a spin-singlet dx2-y2+/-idxy-wave, or chiral d-wave symmetry has recently been suggested to emerge from electron-electron interactions in doped graphene. It has been argued that graphene doped to the van Hove singularity at 1/4 doping, where the density of states diverge, is particularly likely to be a chiral d-wave superconductor. In this review we summarize the currently mounting theoretical evidence for the existence of a chiral d-wave superconducting state in graphene, obtained with methods ranging from mean-field studies of effective Hamiltonians to angle-resolved renormalization group calculations. We further discuss the multiple distinctive properties of the chiral d-wave superconducting state in graphene, as well as its stability in the presence of disorder. We also review the means of enhancing the chiral d-wave state using proximity-induced superconductivity. The appearance of chiral d-wave superconductivity is intimately linked to the hexagonal crystal lattice and we also offer a brief overview of other materials which have also been proposed to be chiral d-wave superconductors.
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20
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Zhang J, Lörscher C, Gu Q, Klemm RA. Is the anisotropy of the upper critical field of Sr2RuO4 consistent with a helical p-wave state? JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:252201. [PMID: 24848586 DOI: 10.1088/0953-8984/26/25/252201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We calculate the angular and temperature T dependencies of the upper critical field Hc2(θ, ϕ, T) for the C4v point group helical p-wave states, assuming a single uniaxial ellipsoidal Fermi surface, Pauli limiting and strong spin-orbit coupling that locks the spin-triplet d-vectors onto the layers. Good fits to the Sr2RuO4 Hc2,a(θ, T) data of Kittaka et al (2009 Phys. Rev. B 80 174514) are obtained. Helical states with d(k) =kˆxxˆ −kˆyy and kˆyxˆ +kˆxy (or kˆxxˆ +kˆyyˆ and kˆyxˆ -kˆxyˆ ) produce Hc2(90°, ϕ, T) that greatly exceed (or do not exhibit) the fourfold azimuthal anisotropy magnitudes observed in Sr2RuO4 by Kittaka et al and by Mao et al (2000 Phys. Rev. Lett. 84 991), respectively.
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Affiliation(s)
- J Zhang
- Department of Physics, University of Science and Technology Beijing, Beijing 100083, People's Republic of China
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21
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Ying YA, Staley NE, Xin Y, Sun K, Cai X, Fobes D, Liu TJ, Mao ZQ, Liu Y. Enhanced spin-triplet superconductivity near dislocations in Sr₂RuO₄. Nat Commun 2014; 4:2596. [PMID: 24201758 DOI: 10.1038/ncomms3596] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2013] [Accepted: 09/11/2013] [Indexed: 11/09/2022] Open
Abstract
Superconductors with a chiral p-wave pairing are of great interest because they could support Majorana modes that could enable the development of topological quantum computing technologies that are robust against decoherence. Sr₂RuO₄ is widely believed to be a chiral p-wave superconductor. Yet, the mechanism by which superconductivity emerges in this, and indeed most other unconventional superconductors, remains unclear. Here we show that the local superconducting transition temperature in the vicinity of lattice dislocations in Sr₂RuO₄ can be up to twice that of its bulk. This is all the more surprising for the fact that disorder is known to easily quench superconductivity in this material. With the help of a phenomenological theory that takes into account the crystalline symmetry near a dislocation and the pairing symmetry of Sr₂RuO₄, we predict that a similar enhancement should emerge as a consequence of symmetry reduction in any superconductor with a two-component order parameter.
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Affiliation(s)
- Y A Ying
- Department of Physics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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22
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Hicks CW, Brodsky DO, Yelland EA, Gibbs AS, Bruin JAN, Barber ME, Edkins SD, Nishimura K, Yonezawa S, Maeno Y, Mackenzie AP. Strong Increase of Tc of Sr2RuO4 Under Both Tensile and Compressive Strain. Science 2014; 344:283-5. [DOI: 10.1126/science.1248292] [Citation(s) in RCA: 222] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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23
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Veenstra CN, Zhu ZH, Raichle M, Ludbrook BM, Nicolaou A, Slomski B, Landolt G, Kittaka S, Maeno Y, Dil JH, Elfimov IS, Haverkort MW, Damascelli A. Spin-orbital entanglement and the breakdown of singlets and triplets in Sr2RuO4 revealed by spin- and angle-resolved photoemission spectroscopy. PHYSICAL REVIEW LETTERS 2014; 112:127002. [PMID: 24724673 DOI: 10.1103/physrevlett.112.127002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2013] [Indexed: 06/03/2023]
Abstract
Spin-orbit coupling has been conjectured to play a key role in the low-energy electronic structure of Sr2RuO4. By using circularly polarized light combined with spin- and angle-resolved photoemission spectroscopy, we directly measure the value of the effective spin-orbit coupling to be 130±30 meV. This is even larger than theoretically predicted and comparable to the energy splitting of the dxy and dxz,yz orbitals around the Fermi surface, resulting in a strongly momentum-dependent entanglement of spin and orbital character in the electronic wavefunction. As demonstrated by the spin expectation value ⟨sk⃗·s-k⃗⟩ calculated for a pair of electrons with zero total momentum, the classification of the Cooper pairs in terms of pure singlets or triplets fundamentally breaks down, necessitating a description of the unconventional superconducting state of Sr2RuO4 in terms of these newly found spin-orbital entangled eigenstates.
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Affiliation(s)
- C N Veenstra
- Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Z-H Zhu
- Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - M Raichle
- Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - B M Ludbrook
- Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - A Nicolaou
- Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada and Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada and Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany
| | - B Slomski
- Physik-Institut, Winterthurerstrasse 190, Universitat Zürich-Irchel, CH-8057 Zürich, Switzerland and Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - G Landolt
- Physik-Institut, Winterthurerstrasse 190, Universitat Zürich-Irchel, CH-8057 Zürich, Switzerland and Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - S Kittaka
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan and Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Y Maeno
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - J H Dil
- Physik-Institut, Winterthurerstrasse 190, Universitat Zürich-Irchel, CH-8057 Zürich, Switzerland and Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - I S Elfimov
- Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada and Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - M W Haverkort
- Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada and Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada and Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany
| | - A Damascelli
- Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada and Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
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24
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Garaud J, Babaev E. Domain walls and their experimental signatures in s+is superconductors. PHYSICAL REVIEW LETTERS 2014; 112:017003. [PMID: 24483921 DOI: 10.1103/physrevlett.112.017003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Indexed: 06/03/2023]
Abstract
Arguments were recently advanced that hole-doped Ba(1-x)K(x)Fe2As2 exhibits the s+is state at certain doping. Spontaneous breaking of time-reversal symmetry in the s+is state dictates that it possess domain wall excitations. Here, we discuss what are the experimentally detectable signatures of domain walls in the s+is state. We find that in this state the domain walls can have a dipolelike magnetic signature (in contrast to the uniform magnetic signature of domain walls p+ip superconductors). We propose experiments where quench-induced domain walls can be stabilized by geometric barriers and observed via their magnetic signature or their influence on the magnetization process, thereby providing an experimental tool to confirm the s+is state.
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Affiliation(s)
- Julien Garaud
- Department of Physics, University of Massachusetts Amherst, Massachusetts 01003, USA and Department of Theoretical Physics, Royal Institute of Technology, Stockholm, SE-10691, Sweden
| | - Egor Babaev
- Department of Physics, University of Massachusetts Amherst, Massachusetts 01003, USA and Department of Theoretical Physics, Royal Institute of Technology, Stockholm, SE-10691, Sweden
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25
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Vadimov V, Silaev M. Predicted nucleation of domain walls in p(x)+ip(y) superconductors by a Z(2) symmetry-breaking transition in external magnetic fields. PHYSICAL REVIEW LETTERS 2013; 111:177001. [PMID: 24206513 DOI: 10.1103/physrevlett.111.177001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2013] [Indexed: 06/02/2023]
Abstract
We show that time reversal symmetry-breaking p(x)+ip(y) wave superconductors undergo several phase transitions subjected to an external magnetic field or supercurrent. In such a system, the discrete Z(2) symmetry can recover before a complete destruction of the order parameter. The domain walls associated with Z(2) symmetry can be created in a controllable way by a magnetic field or current sweep according to the Kibble-Zurek scenario. Such domain wall generation can take place in exotic superconductors like Sr(2)RuO(4), thin films of superfluid (3)He-A, and some heavy fermion compounds.
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Affiliation(s)
- Vasily Vadimov
- Institute for Physics of Microstructures RAS, 603950 Nizhny Novgorod, Russia
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26
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27
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Huo JW, Rice TM, Zhang FC. Spin density wave fluctuations and p-wave pairing in Sr2RuO4. PHYSICAL REVIEW LETTERS 2013; 110:167003. [PMID: 23679633 DOI: 10.1103/physrevlett.110.167003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Indexed: 06/02/2023]
Abstract
Recently, a debate has arisen over which of the two distinct parts of the Fermi surface of Sr(2)RuO(4) is the active part for the chiral p-wave superconductivity exhibited. Early theories proposed p-wave pairing on the two-dimensional γ band, whereas a recent proposal focuses on the one-dimensional (α, β) bands whose nesting pockets are the source of the strong incommensurate spin density wave (SDW) fluctuations. We apply a renormalization group theory to study quasi-one-dimensional repulsive Hubbard chains and explain the form of SDW fluctuations, reconciling the absence of long-range order with their nesting Fermi surface. The mutual exclusion of p-wave pairing and SDW fluctuations in repulsive Hubbard chains favors the assignment of the two-dimensional γ band as the source of p-wave pairing.
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Affiliation(s)
- Jia-Wei Huo
- Department of Physics and Centre of Theoretical and Computational Physics, The University of Hong Kong, Hong Kong SAR, China
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28
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Alicea J. New directions in the pursuit of Majorana fermions in solid state systems. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2012; 75:076501. [PMID: 22790778 DOI: 10.1088/0034-4885/75/7/076501] [Citation(s) in RCA: 477] [Impact Index Per Article: 39.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The 1937 theoretical discovery of Majorana fermions-whose defining property is that they are their own anti-particles-has since impacted diverse problems ranging from neutrino physics and dark matter searches to the fractional quantum Hall effect and superconductivity. Despite this long history the unambiguous observation of Majorana fermions nevertheless remains an outstanding goal. This review paper highlights recent advances in the condensed matter search for Majorana that have led many in the field to believe that this quest may soon bear fruit. We begin by introducing in some detail exotic 'topological' one- and two-dimensional superconductors that support Majorana fermions at their boundaries and at vortices. We then turn to one of the key insights that arose during the past few years; namely, that it is possible to 'engineer' such exotic superconductors in the laboratory by forming appropriate heterostructures with ordinary s-wave superconductors. Numerous proposals of this type are discussed, based on diverse materials such as topological insulators, conventional semiconductors, ferromagnetic metals and many others. The all-important question of how one experimentally detects Majorana fermions in these setups is then addressed. We focus on three classes of measurements that provide smoking-gun Majorana signatures: tunneling, Josephson effects and interferometry. Finally, we discuss the most remarkable properties of condensed matter Majorana fermions-the non-Abelian exchange statistics that they generate and their associated potential for quantum computation.
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Affiliation(s)
- Jason Alicea
- Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
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29
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Mercure JF, Bangura AF, Xu X, Wakeham N, Carrington A, Walmsley P, Greenblatt M, Hussey NE. Upper critical magnetic field far above the paramagnetic pair-breaking limit of superconducting one-dimensional Li0:9Mo6O17 single crystals. PHYSICAL REVIEW LETTERS 2012; 108:187003. [PMID: 22681108 DOI: 10.1103/physrevlett.108.187003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Revised: 09/15/2011] [Indexed: 06/01/2023]
Abstract
The upper critical field H(c2) of purple bronze Li0:9Mo6O17 is found to exhibit a large anisotropy, in quantitative agreement with that expected from the observed electrical resistivity anisotropy. With the field aligned along the most conducting axis, H(c2) increases monotonically with decreasing temperature to a value 5 times larger than the estimated paramagnetic pair-breaking field. Theories for the enhancement of H(c2) invoking spin-orbit scattering or strong-coupling superconductivity are shown to be inadequate in explaining the observed behavior, suggesting that the pairing state in Li0:9Mo6O17 is unconventional and possibly spin triplet.
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Affiliation(s)
- J-F Mercure
- H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, BS8 1TL, United Kingdom
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30
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Taylor E, Kallin C. Intrinsic Hall effect in a multiband chiral superconductor in the absence of an external magnetic field. PHYSICAL REVIEW LETTERS 2012; 108:157001. [PMID: 22587276 DOI: 10.1103/physrevlett.108.157001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Indexed: 05/31/2023]
Abstract
We identify an intrinsic Hall effect in multiband chiral superconductors in the absence of a magnetic field (i.e., an anomalous Hall effect). This effect arises from interband transitions involving time-reversal symmetry-breaking chiral Cooper pairs. We discuss the implications of this effect for the putative chiral p-wave superconductor, Sr2RuO4, and show that it can contribute significantly to Kerr rotation experiments. Since the magnitude of the effect depends on the structure of the order parameter across the bands, this result may be used to distinguish between different models proposed for the superconducting state of Sr2RuO4.
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Affiliation(s)
- Edward Taylor
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada
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31
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Kallin C. Chiral p-wave order in Sr2RuO4. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2012; 75:042501. [PMID: 22790504 DOI: 10.1088/0034-4885/75/4/042501] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Shortly after the discovery in 1994 of superconductivity in Sr(2)RuO(4), it was proposed on theoretical grounds that the superconducting state may have chiral p-wave symmetry analogous to the A phase of superfluid (3)He. Substantial experimental evidence has since accumulated in favor of this pairing symmetry, including several interesting recent results related to broken time-reversal symmetry (BTRS) and vortices with half of the usual superconducting flux quantum. Great interest surrounds the possibility of chiral p-wave order in Sr(2)RuO(4), since this state may exhibit topological order analogous to that of a quantum Hall state, and can support such exotic physics as Majorana fermions and non-Abelian winding statistics, which have been proposed as one route to a quantum computer. However, serious discrepancies remain in trying to connect the experimental results to theoretical predictions for chiral p-wave order. In this paper, I review a broad range of experiments on Sr(2)RuO(4) that are sensitive to p-wave pairing, triplet superconductivity and time-reversal symmetry breaking and compare these experiments to each other and to theoretical predictions. In this context, the evidence for triplet pairing is strong, although some puzzles remain. The 'smoking gun' experimental results for chiral p-wave order, those which directly look for evidence of BTRS in the superconducting state of Sr(2)RuO(4), are most perplexing when the results are compared with each other and to theoretical predictions. Consequently, the case for chiral p-wave superconductivity in Sr(2)RuO(4) remains unresolved, suggesting the need to consider either significant modifications to the standard chiral p-wave models or possible alternative pairing symmetries. Recent ideas along these lines are discussed.
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Affiliation(s)
- Catherine Kallin
- Department of Physics and Astronomy, McMaster University, Hamilton ON L8S 4M1, Canada.
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32
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Wysokiński KI, Annett JF, Györffy BL. Intrinsic optical dichroism in the chiral superconducting state of Sr2RuO4. PHYSICAL REVIEW LETTERS 2012; 108:077004. [PMID: 22401244 DOI: 10.1103/physrevlett.108.077004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Indexed: 05/31/2023]
Abstract
We present an analysis of the Hall conductivity σ(xy)(ω,T) in time reversal symmetry breaking states of exotic superconductors. We find that the dichroic signal is nonzero in systems with interband order parameters. This new intrinsic mechanism may explain the Kerr effect observed in strontium ruthenate and possibly other superconductors. We predict coherence factor effects in the temperature dependence of the imaginary part of the ac Hall conductivity Imσ(xy)(ω,T), which can be tested experimentally.
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Affiliation(s)
- K I Wysokiński
- Institute of Physics, M. Curie-Skłodowska University, Lublin, Poland
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