1
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Fabrizio M. Spin-Liquid Insulators Can Be Landau's Fermi Liquids. PHYSICAL REVIEW LETTERS 2023; 130:156702. [PMID: 37115899 DOI: 10.1103/physrevlett.130.156702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Accepted: 03/23/2023] [Indexed: 06/19/2023]
Abstract
The long search for insulating materials that possess low-energy quasiparticles carrying electron's quantum numbers except charge-inspired by the neutral spin-1/2 excitations, the so-called spinons, exhibited by Anderson's resonating-valence-bond state-seems to have reached a turning point after the discovery of several Mott insulators displaying the same thermal and magnetic properties as metals, including quantum oscillations in a magnetic field. Here, we show that such anomalous behavior is not inconsistent with Landau's Fermi liquid theory of quasiparticles at a Luttinger surface. That is the manifold of zeros within the Brillouin zone of the single-particle Green's function at zero frequency, and which thus defines the spinon Fermi surface conjectured by Anderson.
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Affiliation(s)
- Michele Fabrizio
- International School for Advanced Studies (SISSA), Via Bonomea 265, I-34136 Trieste, Italy
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2
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Stensberg J, Han X, Lee S, McGill SA, Paglione J, Takeuchi I, Kane CL, Wu L. Observation of the Superconducting Proximity Effect from Surface States in SmB_{6}/YB_{6} Thin Film Heterostructures via Terahertz Spectroscopy. PHYSICAL REVIEW LETTERS 2023; 130:096901. [PMID: 36930917 DOI: 10.1103/physrevlett.130.096901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Revised: 08/12/2022] [Accepted: 01/26/2023] [Indexed: 06/18/2023]
Abstract
The ac conduction of epitaxially grown SmB_{6} thin films and superconducting heterostructures of SmB_{6}/YB_{6} are investigated via time-domain terahertz spectroscopy. A two-channel model of thickness-dependent bulk states and thickness-independent surface states accurately describes the measured conductance of bare SmB_{6} thin films, demonstrating the presence of surface states in SmB_{6}. While the observed reductions in the simultaneously measured superconducting gap, transition temperature, and superfluid density of SmB_{6}/YB_{6} heterostructures relative to bare YB_{6} indicate the penetration of proximity-induced superconductivity into the SmB_{6} overlayer; the corresponding SmB_{6}-thickness independence between different heterostructures indicates that the induced superconductivity is predominantly confined to the interface surface state of the SmB_{6}. This study demonstrates the ability of terahertz spectroscopy to probe proximity-induced superconductivity at an interface buried within a heterostructure, and our results show that SmB_{6} behaves as a predominantly insulating bulk surrounded by conducting surface states in both the normal and induced-superconducting states in both terahertz and dc responses, which is consistent with the topological Kondo insulator picture.
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Affiliation(s)
- Jonathan Stensberg
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Xingyue Han
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Seunghun Lee
- Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
- Department of Physics, Pukyong National University, Busan 48513, Republic of Korea
| | - Stephen A McGill
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
| | - Johnpierre Paglione
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - Ichiro Takeuchi
- Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - Charles L Kane
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Liang Wu
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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3
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Charge-neutral fermions and magnetic field-driven instability in insulating YbIr 3Si 7. Nat Commun 2022; 13:394. [PMID: 35046390 PMCID: PMC8770758 DOI: 10.1038/s41467-021-27541-9] [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: 04/21/2021] [Accepted: 11/24/2021] [Indexed: 11/08/2022] Open
Abstract
Kondo lattice materials, where localized magnetic moments couple to itinerant electrons, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, with a dramatic example being recent observations of quantum oscillations and metallic thermal conduction in insulators, implying the emergence of enigmatic charge-neutral fermions. Here, we show that thermal conductivity and specific heat measurements in insulating YbIr3Si7 reveal emergent neutral excitations, whose properties are sensitively changed by a field-driven transition between two antiferromagnetic phases. In the low-field phase, a significant violation of the Wiedemann-Franz law demonstrates that YbIr3Si7 is a charge insulator but a thermal metal. In the high-field phase, thermal conductivity exhibits a sharp drop below 300 mK, indicating a transition from a thermal metal into an insulator/semimetal driven by the magnetic transition. These results suggest that spin degrees of freedom directly couple to the neutral fermions, whose emergent Fermi surface undergoes a field-driven instability at low temperatures.
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4
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Intrinsic Bulk Quantum Oscillations in a Bulk Unconventional Insulator SmB 6. iScience 2020; 23:101632. [PMID: 33145482 PMCID: PMC7593550 DOI: 10.1016/j.isci.2020.101632] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Revised: 08/13/2020] [Accepted: 09/25/2020] [Indexed: 11/24/2022] Open
Abstract
The finding of bulk quantum oscillations in the Kondo insulator SmB6 proved a considerable surprise. Subsequent measurements of bulk quantum oscillations in other correlated insulators including YbB12 lent support to our discovery of a class of bulk unconventional insulators that host bulk quantum oscillations. Here we perform a series of experiments to examine evidence for the intrinsic character of bulk quantum oscillations in floating zone-grown single crystals of SmB6 that have been the subject of our quantum oscillation studies. We present results of thermodynamic, transport, and composition analysis experiments on pristine floating zone-grown single crystals of SmB6 and compare quantum oscillations with metallic LaB6 and elemental aluminum. These results establish the intrinsic origin of quantum oscillations from the insulating bulk of floating zone-grown SmB6. The similarity of the Fermi surface in insulating SmB6 with the conduction-electron Fermi surface in metallic hexaborides is at the heart of a theoretical mystery. No metallic inclusion contribution to quantum oscillations in ultrapure insulating SmB6 Unconventional low energy excitations responsible for bulk quantum oscillations in SmB6 Insulating SmB6 Fermi surface resembles conduction-e- Fermi surface of metallic LaB6
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5
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Han Z, Li T, Zhang L, Sullivan G, Du RR. Anomalous Conductance Oscillations in the Hybridization Gap of InAs/GaSb Quantum Wells. PHYSICAL REVIEW LETTERS 2019; 123:126803. [PMID: 31633941 DOI: 10.1103/physrevlett.123.126803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 05/09/2019] [Indexed: 06/10/2023]
Abstract
We observe the magnetic oscillation of electric conductance in the two-dimensional InAs/GaSb quantum spin Hall insulator. Its insulating bulk origin is unambiguously demonstrated by the antiphase oscillations of the conductance and the resistance. Characteristically, the in-gap oscillation frequency is higher than the Shubnikov-de Haas oscillation close to the conduction band edge in the metallic regime. The temperature dependence shows both thermal activation and smearing effects, which cannot be described by the Lifshitz-Kosevich theory. A two-band Bernevig-Hughes-Zhang model with a large quasiparticle self-energy in the insulating regime is proposed to capture the main properties of the in-gap oscillations.
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Affiliation(s)
- Zhongdong Han
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Tingxin Li
- Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892, USA
| | - Long Zhang
- Kavli Institute for Theoretical Sciences and CAS Center for Excellence, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Gerard Sullivan
- Teledyne Scientific and Imaging, Thousand Oaks, California 91603, USA
| | - Rui-Rui Du
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892, USA
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
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6
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Nonequilibrium Magnetic Oscillation with Cylindrical Vector Beams. Sci Rep 2018; 8:15738. [PMID: 30356070 PMCID: PMC6200753 DOI: 10.1038/s41598-018-33651-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Accepted: 09/26/2018] [Indexed: 11/23/2022] Open
Abstract
Magnetic oscillation is a generic property of electronic conductors under magnetic fields and widely appreciated as a useful probe of their electronic band structure, i.e. the Fermi surface geometry. However, the usage of the strong static magnetic field makes the measurement insensitive to the magnetic order of the target material. That is, the magnetic order is anyhow turned into a forced ferrromagnetic one. Here we theoretically propose an experimental method of measuring the magnetic oscillation in a magnetic-order-resolved way by using the azimuthal cylindrical vector (CV) beam, an example of topological lightwaves. The azimuthal CV beam is unique in that, when focused tightly, it develops a pure longitudinal magnetic field. We argue that this characteristic focusing property and the discrepancy in the relaxation timescale between conduction electrons and localized magnetic moments allow us to develop the nonequilibrium analogue of the magnetic oscillation measurement. Our optical method would be also applicable to metals under the ultra-high pressure of diamond anvil cells.
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7
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Demishev SV, Gilmanov MI, Samarin AN, Semeno AV, Sluchanko NE, Samarin NA, Bogach AV, Shitsevalova NY, Filipov VB, Karasev MS, Glushkov VV. Magnetic resonance probing of ground state in the mixed valence correlated topological insulator SmB 6. Sci Rep 2018; 8:7125. [PMID: 29740044 PMCID: PMC5940907 DOI: 10.1038/s41598-018-25464-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 04/20/2018] [Indexed: 11/09/2022] Open
Abstract
Introducing of topological insulator concept for fluctuating valence compound - samarium hexaboride - has recently initiated a new round of studies aimed to clarify the nature of the ground state in this extraordinary system with strong electron correlations. Here we discuss the data of magnetic resonance in the pristine single crystals of SmB6 measured in 60 GHz cavity experiments at temperatures 1.8-300 K. The microwave study as well as the DC resistivity and Hall effect measurements performed for the different states of SmB6 [110] surface prove definitely the existence of the layer with metallic conductivity increasing under lowering temperature below 5 K. Four lines with the g-factors g ≈ 2 are found to contribute to the ESR-like absorption spectrum that may be attributed to intrinsic paramagnetic centers on the sample's surface, which are robust with respect to the surface treatment. The temperature dependence of integrated intensity I(T) for main paramagnetic signal is found to demonstrate anomalous critical behavior I(T) ~ (T* - T)ν with characteristic temperature T * = 5.34 ± 0.05 K and exponent ν = 0.38 ± 0.03 indicating possible magnetic transition at the SmB6 [110] surface. Additional resonant magnetoabsorption line, which may be associated with either donor-like defects or cyclotron resonance mode corresponding to the mass m c ~ 1.2m0, is reported.
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Affiliation(s)
- S V Demishev
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia.,National Research University Higher School of Economics, Moscow, 101000, Russia
| | - M I Gilmanov
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia.,Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - A N Samarin
- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - A V Semeno
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia.,Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - N E Sluchanko
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia.,Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - N A Samarin
- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - A V Bogach
- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - N Yu Shitsevalova
- Institute for Problems of Materials Science of NASU, Kiev, 03680, Ukraine
| | - V B Filipov
- Institute for Problems of Materials Science of NASU, Kiev, 03680, Ukraine
| | - M S Karasev
- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
| | - V V Glushkov
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700, Moscow region, Russia. .,Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia.
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8
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Chowdhury D, Sodemann I, Senthil T. Mixed-valence insulators with neutral Fermi surfaces. Nat Commun 2018; 9:1766. [PMID: 29720630 PMCID: PMC5932084 DOI: 10.1038/s41467-018-04163-2] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Accepted: 03/28/2018] [Indexed: 11/13/2022] Open
Abstract
Samarium hexaboride is a classic three-dimensional mixed valence system with a high-temperature metallic phase that evolves into a paramagnetic charge insulator below 40 K. A number of recent experiments have suggested the possibility that the low-temperature insulating bulk hosts electrically neutral gapless fermionic excitations. Here we show that a possible ground state of strongly correlated mixed valence insulators—a composite exciton Fermi liquid—hosts a three dimensional Fermi surface of a neutral fermion, that we name the “composite exciton.” We describe the mechanism responsible for the formation of such excitons, discuss the phenomenology of the composite exciton Fermi liquids and make comparison to experiments in SmB6. Samarium hexaboride is a candidate topological insulator but recent experiments have found behaviour indicative of a metallic Fermi liquid phase. Here the authors show that the conflicting observations can be accommodated by a model where strong interactions drive the formation of exotic neutral quasiparticles.
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Affiliation(s)
- Debanjan Chowdhury
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
| | - Inti Sodemann
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,Max-Planck Institute for the Physics of Complex Systems, Dresden, 01187, Germany
| | - T Senthil
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
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9
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Liu H, Hartstein M, Wallace GJ, Davies AJ, Hatnean MC, Johannes MD, Shitsevalova N, Balakrishnan G, Sebastian SE. Fermi surfaces in Kondo insulators. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:16LT01. [PMID: 29300180 DOI: 10.1088/1361-648x/aaa522] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We report magnetic quantum oscillations measured using torque magnetisation in the Kondo insulator YbB12 and discuss the potential origin of the underlying Fermi surface. Observed quantum oscillations as well as complementary quantities such as a finite linear specific heat capacity in YbB12 exhibit similarities with the Kondo insulator SmB6, yet also crucial differences. Small heavy Fermi sections are observed in YbB12 with similarities to the neighbouring heavy fermion semimetallic Fermi surface, in contrast to large light Fermi surface sections in SmB6 which are more similar to the conduction electron Fermi surface. A rich spectrum of theoretical models is suggested to explain the origin across different Kondo insulating families of a bulk Fermi surface potentially from novel itinerant quasiparticles that couple to magnetic fields, yet do not couple to weak DC electric fields.
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Affiliation(s)
- Hsu Liu
- Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
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10
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Wu Q, Sun L. Puzzle maker in SmB 6: accompany-type valence fluctuation state. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2017; 80:112501. [PMID: 28937971 DOI: 10.1088/1361-6633/aa7e3a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In recent years, studying the Kondo insulator SmB6, a strongly correlated electron material that has been puzzling the community for decades, has again become an attractive topic due to the discovery of its unusual metallic surface state coexisting with the bulk insulating state. Many efforts have been made to understand the microphysics in SmB6, but some puzzles that have been hotly debated and argued have not been solved. In this article, based on the latest progress made in our high-pressure studies on SmB6 and the accumulating results reported by other groups, we propose a notion named the 'accompany-type valence fluctuation state', which possibly coexists with the bulk Kondo insulating ground state of SmB6. We expect that this notion could be taken as a common starting point for understanding in a unified way most of the low-temperature phenomena observed by different experimental investigations on SmB6, thus promoting the deciphering of the puzzles. We also expect that this notion could attract rigorous theoretical interpretation and further experimental investigation, or stimulate better thinking on the physics in SmB6.
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Affiliation(s)
- Qi Wu
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
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11
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Min CH, Goth F, Lutz P, Bentmann H, Kang BY, Cho BK, Werner J, Chen KS, Assaad F, Reinert F. Matching DMFT calculations with photoemission spectra of heavy fermion insulators: universal properties of the near-gap spectra of SmB 6. Sci Rep 2017; 7:11980. [PMID: 28931836 PMCID: PMC5607333 DOI: 10.1038/s41598-017-12080-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Accepted: 09/04/2017] [Indexed: 11/11/2022] Open
Abstract
Paramagnetic heavy fermion insulators consist of fully occupied quasiparticle bands inherent to Fermi liquid theory. The gap emergence below a characteristic temperature is the ultimate sign of coherence for a many-body system, which in addition can induce a non-trivial band topology. Here, we demonstrate a simple and efficient method to compare a model study and an experimental result for heavy fermion insulators. The temperature dependence of the gap formation in both local moment and mixed valence regimes is captured within the dynamical mean field (DMFT) approximation to the periodic Anderson model (PAM). Using the topological coherence temperature as the scaling factor and choosing the input parameter set within the mixed valence regime, we can unambiguously link the theoretical energy scales to the experimental ones. As a particularly important result, we find improved consistency between the scaled DMFT density of states and the photoemission near-gap spectra of samarium hexaboride (SmB6).
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Affiliation(s)
- Chul-Hee Min
- Experimentelle Physik VII and Röntgen Research Center for Complex Materials (RCCM), Universität Würzburg, 97074, Würzburg, Germany.
| | - F Goth
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074, Würzburg, Germany
| | - P Lutz
- Experimentelle Physik VII and Röntgen Research Center for Complex Materials (RCCM), Universität Würzburg, 97074, Würzburg, Germany
| | - H Bentmann
- Experimentelle Physik VII and Röntgen Research Center for Complex Materials (RCCM), Universität Würzburg, 97074, Würzburg, Germany
| | - B Y Kang
- School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Korea
| | - B K Cho
- School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Korea
| | - J Werner
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074, Würzburg, Germany
| | - K-S Chen
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074, Würzburg, Germany
| | - F Assaad
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074, Würzburg, Germany
| | - F Reinert
- Experimentelle Physik VII and Röntgen Research Center for Complex Materials (RCCM), Universität Würzburg, 97074, Würzburg, Germany
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12
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Erten O, Chang PY, Coleman P, Tsvelik AM. Skyrme Insulators: Insulators at the Brink of Superconductivity. PHYSICAL REVIEW LETTERS 2017; 119:057603. [PMID: 28949703 DOI: 10.1103/physrevlett.119.057603] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Indexed: 06/07/2023]
Abstract
Current theories of superfluidity are based on the idea of a coherent quantum state with topologically protected quantized circulation. When this topological protection is absent, as in the case of ^{3}He-A, the coherent quantum state no longer supports persistent superflow. Here, we argue that the loss of topological protection in a superconductor gives rise to an insulating ground state. We specifically introduce the concept of a Skyrme insulator to describe the coherent dielectric state that results from the topological failure of superflow carried by a complex-vector order parameter. We apply this idea to the case of SmB_{6}, arguing that the observation of a diamagnetic Fermi surface within an insulating bulk can be understood as a realization of this state. Our theory enables us to understand the linear specific heat of SmB_{6} in terms of a neutral Majorana Fermi sea and leads us to predict that in low fields of order a Gauss, SmB_{6} will develop a Meissner effect.
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Affiliation(s)
- Onur Erten
- Center for Materials Theory, Rutgers University, Piscataway, New Jersey 08854, USA
- Max Planck Institute for the Physics of Complex Systems, D-01187 Dresden, Germany
| | - Po-Yao Chang
- Center for Materials Theory, Rutgers University, Piscataway, New Jersey 08854, USA
| | - Piers Coleman
- Center for Materials Theory, Rutgers University, Piscataway, New Jersey 08854, USA
- Department of Physics, Royal Holloway, University of London, Egham, Surrey TW20 0EX, United Kingdom
| | - Alexei M Tsvelik
- Division of Condensed Matter Physics and Material Science, Brookhaven National Laboratory, Upton, New York 11973, USA
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13
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Knolle J, Cooper NR. Anomalous de Haas-van Alphen Effect in InAs/GaSb Quantum Wells. PHYSICAL REVIEW LETTERS 2017; 118:176801. [PMID: 28498702 DOI: 10.1103/physrevlett.118.176801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Indexed: 06/07/2023]
Abstract
The de Haas-van Alphen effect describes the periodic oscillation of the magnetization in a material as a function of an inverse applied magnetic field. It forms the basis of a well established procedure for measuring Fermi surface properties, and its observation is typically taken as a direct signature of a system being metallic. However, certain insulators can show similar oscillations of the magnetization from quantization of the energies of electron states in filled bands. Recently, the theory of such an anomalous dHvAE (AdHvAE) was worked out, but there has not yet been a clear experimental observation. Here, we show that the inverted narrow gap regime of InAs/GaSb quantum wells is an ideal platform for the observation of the AdHvAE. From our microscopic calculations, we make quantitative predictions for the relevant magnetic field and temperature regimes, and we describe unambiguous experimental signatures.
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Affiliation(s)
- Johannes Knolle
- T.C.M. Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Nigel R Cooper
- T.C.M. Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
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14
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Jian SK, Lin CH, Maciejko J, Yao H. Emergence of Supersymmetric Quantum Electrodynamics. PHYSICAL REVIEW LETTERS 2017; 118:166802. [PMID: 28474942 DOI: 10.1103/physrevlett.118.166802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Indexed: 06/07/2023]
Abstract
Supersymmetric (SUSY) gauge theories such as the minimal supersymmetric standard model play a fundamental role in modern particle physics, but have not been verified so far in nature. Here, we show that a SUSY gauge theory with dynamical gauge bosons and fermionic gauginos emerges naturally at the pair-density-wave (PDW) quantum phase transition on the surface of a correlated topological insulator hosting three Dirac cones, such as the topological Kondo insulator SmB_{6}. At the quantum tricritical point between the surface Dirac semimetal and nematic PDW phases, three massless bosonic Cooper pair fields emerge as the superpartners of three massless surface Dirac fermions. The resulting low-energy effective theory is the supersymmetric XYZ model, which is dual by mirror symmetry to N=2 supersymmetric quantum electrodynamics in 2+1 dimensions, providing a first example of emergent supersymmetric gauge theory in condensed matter systems. Supersymmetry allows us to determine certain critical exponents and the optical conductivity of the surface states at the strongly coupled tricritical point exactly, which may be measured in future experiments.
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Affiliation(s)
- Shao-Kai Jian
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
| | - Chien-Hung Lin
- Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
| | - Joseph Maciejko
- Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
- Theoretical Physics Institute, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
- Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
| | - Hong Yao
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
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15
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Knolle J, Cooper NR. Excitons in topological Kondo insulators: Theory of thermodynamic and transport anomalies in SmB_{6}. PHYSICAL REVIEW LETTERS 2017; 118:096604. [PMID: 28306303 DOI: 10.1103/physrevlett.118.096604] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Indexed: 06/06/2023]
Abstract
Kondo insulating materials lie outside the usual dichotomy of weakly versus correlated-band versus Mott-insulators. They are metallic at high temperatures but resemble band insulators at low temperatures because of the opening of an interaction-induced band gap. The first discovered Kondo insulator (KI) SmB_{6} has been predicted to form a topological KI (TKI). However, since its discovery thermodynamic and transport anomalies have been observed that have defied a theoretical explanation. Enigmatic signatures of collective modes inside the charge gap are seen in specific heat, thermal transport, and quantum oscillation experiments in strong magnetic fields. Here, we show that TKIs are susceptible to the formation of excitons and magnetoexcitons. These charge neutral composite particles can account for long-standing anomalies in SmB_{6}.
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Affiliation(s)
- Johannes Knolle
- T.C.M. Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Nigel R Cooper
- T.C.M. Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
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