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He G, Peis L, Cuddy EF, Zhao Z, Li D, Zhang Y, Stumberger R, Moritz B, Yang H, Gao H, Devereaux TP, Hackl R. Anharmonic strong-coupling effects at the origin of the charge density wave in CsV 3Sb 5. Nat Commun 2024; 15:1895. [PMID: 38429269 PMCID: PMC10907679 DOI: 10.1038/s41467-024-45865-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Accepted: 02/06/2024] [Indexed: 03/03/2024] Open
Abstract
The formation of charge density waves is a long-standing open problem, particularly in dimensions higher than one. Various observations in the vanadium antimonides discovered recently further underpin this notion. Here, we study the Kagome metal CsV3Sb5 using polarized inelastic light scattering and density functional theory calculations. We observe a significant gap anisotropy with 2 Δ max / k B T CDW ≈ 20 , far beyond the prediction of mean-field theory. The analysis of the A1g and E2g phonons, including those emerging below TCDW, indicates strong phonon-phonon coupling, presumably mediated by a strong electron-phonon interaction. Similarly, the asymmetric Fano-type lineshape of the A1g amplitude mode suggests strong electron-phonon coupling below TCDW. The large electronic gap, the enhanced anharmonic phonon-phonon coupling, and the Fano shape of the amplitude mode combined are more supportive of a strong-coupling phonon-driven charge density wave transition than of a Fermi surface instability or an exotic mechanism in CsV3Sb5.
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Affiliation(s)
- Ge He
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, Garching, 85748, Germany.
- Department of Physics, University College Cork, College Road, Cork, T12 K8AF, Ireland.
| | - Leander Peis
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, Garching, 85748, Germany
- School of Natural Sciences, Technische Universität München, Garching, 85748, Germany
- IFW Dresden, Helmholtzstrasse 20, Dresden, 01069, Germany
- Capgemini, Frankfurter Ring 81, 80807, München, Germany
| | - Emma Frances Cuddy
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA
| | - Zhen Zhao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Dong Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Yuhang Zhang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Romona Stumberger
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, Garching, 85748, Germany
- School of Natural Sciences, Technische Universität München, Garching, 85748, Germany
- Robert Bosch GmbH, Robert-Bosch-Campus 1, 71272, Renningen, Germany
| | - Brian Moritz
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA
| | - Haitao Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
| | - Hongjun Gao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Thomas Peter Devereaux
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA.
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA.
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA.
| | - Rudi Hackl
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, Garching, 85748, Germany.
- School of Natural Sciences, Technische Universität München, Garching, 85748, Germany.
- IFW Dresden, Helmholtzstrasse 20, Dresden, 01069, Germany.
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2
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Zhang H, Yan C, Ge Z, Weinert M, Li L. Impenetrable Barrier at the Metal-Mott Insulator Junction in Polymorphic 1H and 1T NbSe 2 Lateral Heterostructure. J Phys Chem Lett 2022; 13:10713-10721. [PMID: 36367815 DOI: 10.1021/acs.jpclett.2c02546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
When a metal makes contact with a band insulator, charge transfer occurs across the interface leading to band bending and a Schottky barrier with rectifying behavior. The nature of metal-Mott insulator junctions, however, is still debated due to challenges in experimental probes of such vertical heterojunctions with buried interfaces. Here, we grow lateral polymorphic heterostructures of single-layer metallic 1H and Mott insulating 1T NbSe2 by molecular beam epitaxy. We find a one-dimensional metallic channel along the interface due to the appearance of quasiparticle states with an intensity decay following 1/x2, indicating an impenetrable barrier. Near the interface, the Mott gap exhibits a strong spatial dependence arising from the difference in lattice constants between the two phases, consistent with our density functional theory calculations. These results provide clear experimental evidence for an impenetrable barrier at the metal-Mott insulator junction and the high tunability of a Mott insulator by strain.
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Affiliation(s)
- Huimin Zhang
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
- State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China
| | - Chenhui Yan
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Zhuozhi Ge
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Michael Weinert
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53201, United States
| | - Lian Li
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
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3
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Observation of anomalous amplitude modes in the kagome metal CsV 3Sb 5. Nat Commun 2022; 13:3461. [PMID: 35710635 PMCID: PMC9203454 DOI: 10.1038/s41467-022-31162-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2022] [Accepted: 06/03/2022] [Indexed: 11/09/2022] Open
Abstract
The kagome lattice provides a fertile platform to explore novel symmetry-breaking states. Charge-density wave (CDW) instabilities have been recently discovered in a new kagome metal family, commonly considered to arise from Fermi-surface instabilities. Here we report the observation of Raman-active CDW amplitude modes in CsV3Sb5, which are collective excitations typically thought to emerge out of frozen soft phonons, although phonon softening is elusive experimentally. The amplitude modes strongly hybridize with other superlattice modes, imparting them with clear temperature-dependent frequency shift and broadening, rarely seen in other known CDW materials. Both the mode mixing and the large amplitude mode frequencies suggest that the CDW exhibits the character of strong electron-phonon coupling, a regime in which phonon softening can cease to exist. Our work highlights the importance of the lattice degree of freedom in the CDW formation and points to the complex nature of the mechanism. The mechanism of the charge density wave in kagome metals is not fully understood. Here, the authors report the observation of unusual large-frequency collective lattice excitations, or amplitude modes, in CsV3Sb5 in the absence of phonon mode softening, evidencing the strong electron-phonon coupling regime.
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4
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Dong Q, Pan J, Li S, Fang Y, Lin T, Liu S, Liu B, Li Q, Huang F, Liu B. Record-High Superconductivity in Transition Metal Dichalcogenides Emerged in Compressed 2H-TaS 2. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2103168. [PMID: 34936715 DOI: 10.1002/adma.202103168] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 12/17/2021] [Indexed: 06/14/2023]
Abstract
Pressure has always been an effective method for uncovering novel phenomena and properties in condensed matter physics. Here, an electrical transport study is carried on 2H-TaS2 up to ≈208 GPa, and an unexpected superconducting state (SC-II) emerging around 86.1 GPa with an initial critical temperature (Tc ) of 9.6 K is found. As pressure increases, the Tc enhances rapidly and reaches a maximum of 16.4 K at 157.4 GPa, which sets a new record for transition metal dichalcogenides (TMDs). The original superconducting state (SC-I) is found to be re-enhanced above 100 GPa after the recession around 10 GPa, and coexists with SC-II to the highest pressure applied in this work. In situ high-pressure X-ray diffraction and Hall effect measurements reveal that the occurrence of SC-II is accompanied by a structural modification and a concurrent enhancement of hole carrier density. The new high-Tc superconducting state in 2H-TaS2 can be attributed to the change of the electronic states near the Fermi surface, owing to pressure-induced interlayer modulation. It is the first time finding this remarkable superconducting state in TMDs, which not only brings a new broad of perspective on layered materials but also expands the field of pressure-modified superconductivity.
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Affiliation(s)
- Qing Dong
- State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012, China
| | - Jie Pan
- State Key Laboratory of High-Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China
| | - Shujia Li
- State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012, China
| | - Yuqiang Fang
- State Key Laboratory of High-Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Tao Lin
- State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012, China
| | - Shuang Liu
- State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012, China
| | - Bo Liu
- State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012, China
| | - Quanjun Li
- State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012, China
| | - Fuqiang Huang
- State Key Laboratory of High-Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China
- State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China
| | - Bingbing Liu
- State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012, China
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5
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Breslavetz I, Delhomme A, Pelini T, Pawbake A, Vaclavkova D, Orlita M, Potemski M, Measson MA, Faugeras C. Spatially resolved optical spectroscopy in extreme environment of low temperature, high magnetic fields and high pressure. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:123909. [PMID: 34972398 DOI: 10.1063/5.0070934] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 12/01/2021] [Indexed: 06/14/2023]
Abstract
We present an experimental setup developed to perform optical spectroscopy experiments (Raman scattering and photoluminescence measurements) with a micrometer spatial resolution in an extreme environment of low temperature, high magnetic field, and high pressure. This unique experimental setup, to the best of our knowledge, allows us to deeply explore the phase diagram of condensed matter systems by independently tuning these three thermodynamic parameters while monitoring the low-energy excitations (electronic, phononic, or magnetic excitations) to spatially map the Raman scattering response or to investigate objects with low dimensions. We apply this technique to bulk FePS3, a layered antiferromagnet with a Néel temperature of T ≈ 120 K.
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Affiliation(s)
- I Breslavetz
- LNCMI, UPR 3228, CNRS, EMFL, Université Grenoble Alpes, 38000 Grenoble, France
| | - A Delhomme
- LNCMI, UPR 3228, CNRS, EMFL, Université Grenoble Alpes, 38000 Grenoble, France
| | - T Pelini
- LNCMI, UPR 3228, CNRS, EMFL, Université Grenoble Alpes, 38000 Grenoble, France
| | - A Pawbake
- LNCMI, UPR 3228, CNRS, EMFL, Université Grenoble Alpes, 38000 Grenoble, France
| | - D Vaclavkova
- LNCMI, UPR 3228, CNRS, EMFL, Université Grenoble Alpes, 38000 Grenoble, France
| | - M Orlita
- LNCMI, UPR 3228, CNRS, EMFL, Université Grenoble Alpes, 38000 Grenoble, France
| | - M Potemski
- LNCMI, UPR 3228, CNRS, EMFL, Université Grenoble Alpes, 38000 Grenoble, France
| | - M-A Measson
- Institut Neel, CNRS, Université Grenoble Alpes, 38000 Grenoble, France
| | - C Faugeras
- LNCMI, UPR 3228, CNRS, EMFL, Université Grenoble Alpes, 38000 Grenoble, France
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6
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Puviani M, Baum A, Ono S, Ando Y, Hackl R, Manske D. Calculation of an Enhanced A_{1g} Symmetry Mode Induced by Higgs Oscillations in the Raman Spectrum of High-Temperature Cuprate Superconductors. PHYSICAL REVIEW LETTERS 2021; 127:197001. [PMID: 34797154 DOI: 10.1103/physrevlett.127.197001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 05/20/2021] [Accepted: 09/30/2021] [Indexed: 06/13/2023]
Abstract
In superconductors the Anderson-Higgs mechanism allows for the existence of a collective amplitude (Higgs) mode which can couple to eV light mainly in a nonlinear Raman-like process. The experimental nonequilibrium results on isotropic superconductors have been explained going beyond the BCS theory including the Higgs mode. Furthermore, in anisotropic d-wave superconductors strong interaction effects with other modes are expected. Here we calculate the Raman contribution of the Higgs mode from a new perspective, including many-body Higgs oscillations effects and their consequences in conventional, spontaneous Raman spectroscopy. Our results suggest a significant contribution to the intensity of the A_{1g} symmetry Raman spectrum in d-wave superconductors. In order to test our theory, we predict the presence of measurable characteristic oscillations in THz quench-optical probe time-dependent reflectivity experiments.
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Affiliation(s)
- M Puviani
- Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
| | - A Baum
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
| | - S Ono
- Central Research Institute of Electric Power Industry, Yokosuka, 240-0196 Kanagawa, Japan
| | - Y Ando
- Institute of Physics II, University of Cologne, 50937 Köln, Germany
| | - R Hackl
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
| | - D Manske
- Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
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7
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Abstract
Low-dimensional (LD) transition metal dichalcogenides (TMDs) in the form of nanoflakes, which consist of one or several layers, are the subject of intensive fundamental and applied research. The tuning of the electronic properties of the LD-TMDs are commonly related with applied strains and strain gradients, which can strongly affect their polar properties via piezoelectric and flexoelectric couplings. Using the density functional theory and phenomenological Landau approach, we studied the bended 2H-MoS2 monolayer and analyzed its flexoelectric and piezoelectric properties. The dependences of the dipole moment, strain, and strain gradient on the coordinate along the layer were calculated. From these dependences, the components of the flexoelectric and piezoelectric tensors have been determined and analyzed. Our results revealed that the contribution of the flexoelectric effect dominates over the piezoelectric effect in both in-plane and out-of-plane directions of the monolayer. In accordance with our calculations, a realistic strain gradient of about 1 nm−1 can induce an order of magnitude higher than the flexoelectric response in comparison with the piezoelectric reaction. The value of the dilatational flexoelectric coefficient is almost two times smaller than the shear component. It appeared that the components of effective flexoelectric and piezoelectric couplings can be described by parabolic dependences of the corrugation. Obtained results are useful for applications of LD-TMDs in strain engineering and flexible electronics.
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8
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Kvashnin Y, VanGennep D, Mito M, Medvedev SA, Thiyagarajan R, Karis O, Vasiliev AN, Eriksson O, Abdel-Hafiez M. Coexistence of Superconductivity and Charge Density Waves in Tantalum Disulfide: Experiment and Theory. PHYSICAL REVIEW LETTERS 2020; 125:186401. [PMID: 33196259 DOI: 10.1103/physrevlett.125.186401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 08/18/2020] [Accepted: 09/25/2020] [Indexed: 06/11/2023]
Abstract
The coexistence of charge density wave (CDW) and superconductivity in tantalum disulfide (2H-TaS_{2}) at low temperature is boosted by applying hydrostatic pressures to study both vibrational and magnetic transport properties. Around P_{c}, we observe a superconducting dome with a maximum superconducting transition temperature T_{c}=9.1 K. First-principles calculations of the electronic structure predict that, under ambient conditions, the undistorted structure is characterized by a phonon instability at finite momentum close to the experimental CDW wave vector. Upon compression, this instability is found to disappear, indicating the suppression of CDW order. The calculations reveal an electronic topological transition (ETT), which occurs before the suppression of the phonon instability, suggesting that the ETT alone is not directly causing the structural change in the system. The temperature dependence of the first vortex penetration field has been experimentally obtained by two independent methods. While a d wave and single-gap BCS prediction cannot describe the lower critical field H_{c1} data, the temperature dependence of the H_{c1} can be well described by a single-gap anisotropic s-wave order parameter.
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Affiliation(s)
- Y Kvashnin
- Uppsala University, Department of Physics and Astronomy, Box 516, SE-751 20 Uppsala, Sweden
| | - D VanGennep
- Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - M Mito
- Graduate School of Engineering, Kyushu Institute of Technology, Fukuoka 804-8550, Japan
| | - S A Medvedev
- Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
| | - R Thiyagarajan
- Institut für Festkörper- und Materialphysik, Technische Universität Dresden, 01069 Dresden, Germany
| | - O Karis
- Uppsala University, Department of Physics and Astronomy, Box 516, SE-751 20 Uppsala, Sweden
| | - A N Vasiliev
- Ural Federal University, Yekaterinburg 620002, Russia
- Lomonosov Moscow State University, Moscow 119991, Russia
- National Research South Ural State University, Chelyabinsk 454080, Russia
| | - O Eriksson
- Uppsala University, Department of Physics and Astronomy, Box 516, SE-751 20 Uppsala, Sweden
- School of Science and Technology, Örebro University, SE-701 82 Örebro, Sweden
| | - M Abdel-Hafiez
- Uppsala University, Department of Physics and Astronomy, Box 516, SE-751 20 Uppsala, Sweden
- Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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9
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Kumar D, Singh B, Kumar R, Kumar M, Kumar P. Anisotropic electron-photon-phonon coupling in layered MoS 2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:415702. [PMID: 32512557 DOI: 10.1088/1361-648x/ab9a7a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 06/08/2020] [Indexed: 06/11/2023]
Abstract
Transition metal dichalcogenide, MoS2has attracted a lot of attention recently owing to its tunable visible range band gap, and anisotropic electronic and transport properties. Here, we report comprehensive inelastic light scattering measurements on both chemical vapor deposition grown (horizontally and vertically aligned) flakes, and mechanically exfoliated flakes of single crystal MoS2. We probe the anisotropic optical response by studying the polarization dependence intensity of the Raman active phonon modes as a function of different incident photon energy and flake thickness. Our polarization dependent Raman studies reveal strong anisotropic behavior reflected in the anomalous renormalization of the modes intensity as a function of flake thickness, phonons and photon energy. Our observations reflect the strong anisotropic light-matter interaction in this high crystalline symmetric layered MoS2system, especially for the in-plane vibrations, crucial for understanding as well as future applications of these materials.
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Affiliation(s)
- Deepu Kumar
- School of Basic Sciences, Indian Institute of Technology Mandi, Mandi-175005, India
| | - Birender Singh
- School of Basic Sciences, Indian Institute of Technology Mandi, Mandi-175005, India
| | - Rahul Kumar
- Department of Electrical Engineering, Indian Institute of Technology Jodhpur, Jodhpur-342037, India
| | - Mahesh Kumar
- Department of Electrical Engineering, Indian Institute of Technology Jodhpur, Jodhpur-342037, India
| | - Pradeep Kumar
- School of Basic Sciences, Indian Institute of Technology Mandi, Mandi-175005, India
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10
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Kurkjian H, Tempere J, Klimin SN. Linear response of a superfluid Fermi gas inside its pair-breaking continuum. Sci Rep 2020; 10:11591. [PMID: 32665570 PMCID: PMC7360786 DOI: 10.1038/s41598-020-65371-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Accepted: 04/20/2020] [Indexed: 11/09/2022] Open
Abstract
We study the signatures of the collective modes of a superfluid Fermi gas in its linear response functions for the order-parameter and density fluctuations in the Random Phase Approximation (RPA). We show that a resonance associated to the Popov-Andrianov (or sometimes "Higgs") mode is visible inside the pair-breaking continuum at all values of the wavevector q, not only in the (order-parameter) modulus-modulus response function but also in the modulus-density and density-density responses. At nonzero temperature, the resonance survives in the presence of thermally broken pairs even until the vicinity of the critical temperature Tc, and coexists with both the Anderson-Bogoliubov modes at temperatures comparable to the gap Δ and with the low-velocity phononic mode predicted by RPA near Tc. The existence of a Popov-Andrianov-"Higgs" resonance is thus a robust, generic feature of the high-energy phenomenology of pair-condensed Fermi gases, and should be accessible to state-of-the-art cold atom experiments.
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Affiliation(s)
- H Kurkjian
- TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610, Antwerp, Belgium.
| | - J Tempere
- TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610, Antwerp, Belgium
| | - S N Klimin
- TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610, Antwerp, Belgium
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11
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Patterns and driving forces of dimensionality-dependent charge density waves in 2H-type transition metal dichalcogenides. Nat Commun 2020; 11:2406. [PMID: 32415071 PMCID: PMC7229047 DOI: 10.1038/s41467-020-15715-w] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Accepted: 03/26/2020] [Indexed: 12/02/2022] Open
Abstract
Charge density wave (CDW) is a startling quantum phenomenon, distorting a metallic lattice into an insulating state with a periodically modulated charge distribution. Astonishingly, such modulations appear in various patterns even within the same family of materials. Moreover, this phenomenon features a puzzling diversity in its dimensional evolution. Here, we propose a general framework, unifying distinct trends of CDW ordering in an isoelectronic group of materials, 2H-MX2 (M = Nb, Ta and X = S, Se). We show that while NbSe2 exhibits a strongly enhanced CDW order in two dimensions, TaSe2 and TaS2 behave oppositely, with CDW being absent in NbS2 entirely. Such a disparity is demonstrated to arise from a competition of ionic charge transfer, electron-phonon coupling, and electron correlation. Despite its simplicity, our approach can, in principle, explain dimensional dependence of CDW in any material, thereby shedding new light on this intriguing quantum phenomenon and its underlying mechanisms. The dimensional dependence of charge density wave (CDW) in two-dimensional dichalcogenides remains puzzled. Here, Lin et al. study trends of CDW ordering in an isoelectronic group of materials 2H-MX2 and provide a unified understanding involving several microscopic factors.
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12
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Chu H, Kim MJ, Katsumi K, Kovalev S, Dawson RD, Schwarz L, Yoshikawa N, Kim G, Putzky D, Li ZZ, Raffy H, Germanskiy S, Deinert JC, Awari N, Ilyakov I, Green B, Chen M, Bawatna M, Cristiani G, Logvenov G, Gallais Y, Boris AV, Keimer B, Schnyder AP, Manske D, Gensch M, Wang Z, Shimano R, Kaiser S. Phase-resolved Higgs response in superconducting cuprates. Nat Commun 2020; 11:1793. [PMID: 32286291 PMCID: PMC7156672 DOI: 10.1038/s41467-020-15613-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Accepted: 03/02/2020] [Indexed: 11/29/2022] Open
Abstract
In high-energy physics, the Higgs field couples to gauge bosons and fermions and gives mass to their elementary excitations. Experimentally, such couplings can be inferred from the decay product of the Higgs boson, i.e., the scalar (amplitude) excitation of the Higgs field. In superconductors, Cooper pairs bear a close analogy to the Higgs field. Interaction between the Cooper pairs and other degrees of freedom provides dissipation channels for the amplitude mode, which may reveal important information about the microscopic pairing mechanism. To this end, we investigate the Higgs (amplitude) mode of several cuprate thin films using phase-resolved terahertz third harmonic generation (THG). In addition to the heavily damped Higgs mode itself, we observe a universal jump in the phase of the driven Higgs oscillation as well as a non-vanishing THG above Tc. These findings indicate coupling of the Higgs mode to other collective modes and potentially a nonzero pairing amplitude above Tc. Interaction between Cooper pairs and other collective excitations may reveal important information about the pairing mechanism. Here, the authors observe a universal jump in the phase of the driven Higgs oscillations in cuprate thin films, indicating the presence of a coupled collective mode, as well as a nonvanishing Higgs-like response at high temperatures, suggesting a potential nonzero pairing amplitude above Tc.
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Affiliation(s)
- Hao Chu
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany.,4th Physics Institute, University of Stuttgart, 70569, Stuttgart, Germany.,Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Min-Jae Kim
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany.,4th Physics Institute, University of Stuttgart, 70569, Stuttgart, Germany
| | - Kota Katsumi
- Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan
| | - Sergey Kovalev
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Robert David Dawson
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Lukas Schwarz
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Naotaka Yoshikawa
- Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan
| | - Gideok Kim
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Daniel Putzky
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Zhi Zhong Li
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Saclay, 91405, Orsay, France
| | - Hélène Raffy
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Saclay, 91405, Orsay, France
| | - Semyon Germanskiy
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Jan-Christoph Deinert
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Nilesh Awari
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany.,University of Groningen, 9747 AG, Groningen, Netherlands
| | - Igor Ilyakov
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Bertram Green
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Min Chen
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany.,Technische Universität Berlin, Institut für Optik und Atomare Physik, Strasse des 17. Juni 135, 10623, Berlin, Germany
| | - Mohammed Bawatna
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Georg Cristiani
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Gennady Logvenov
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Yann Gallais
- Laboratoire Matériaux et Phénomènes Quantiques (UMR 7162 CNRS), Université de Paris, Bâtiment Condorcet, 75205, Paris Cedex 13, France
| | - Alexander V Boris
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Bernhard Keimer
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Andreas P Schnyder
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Dirk Manske
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
| | - Michael Gensch
- Technische Universität Berlin, Institut für Optik und Atomare Physik, Strasse des 17. Juni 135, 10623, Berlin, Germany.,German Aerospace Center (DLR), Institute of Optical Sensor Systems, Rutherfordstrasse 2, 12489, Berlin, Germany
| | - Zhe Wang
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany. .,Institute of Physics II, University of Cologne, 50937, Cologne, Germany.
| | - Ryo Shimano
- Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan. .,Cryogenic Research Center, University of Tokyo, Hongo, Tokyo, 113-0032, Japan.
| | - Stefan Kaiser
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany. .,4th Physics Institute, University of Stuttgart, 70569, Stuttgart, Germany.
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13
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Classification and characterization of nonequilibrium Higgs modes in unconventional superconductors. Nat Commun 2020; 11:287. [PMID: 31941881 PMCID: PMC6962398 DOI: 10.1038/s41467-019-13763-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 11/26/2019] [Indexed: 11/17/2022] Open
Abstract
Recent findings of new Higgs modes in unconventional superconductors require a classification and characterization of the modes allowed by nontrivial gap symmetry. Here we develop a theory for a tailored nonequilibrium quantum quench to excite all possible oscillation symmetries of a superconducting condensate. We show that both a finite momentum transfer and quench symmetry allow for an identification of the resulting Higgs oscillations. These serve as a fingerprint for the ground state gap symmetry. We provide a classification scheme of these oscillations and the quench symmetry based on group theory for the underlying lattice point group. For characterization, analytic calculations as well as full scale numeric simulations of the transient optical response resulting from an excitation by a realistic laser pulse are performed. Our classification of Higgs oscillations allows us to distinguish between different symmetries of the superconducting condensate. The lately reported Higgs modes in unconventional superconductors require a classification and characterization allowed by nontrivial symmetry of the gap and the quench pulses. Here, the authors provide a classification scheme of Higgs oscillations with their excitation processes allowing them to distinguish between different symmetries of the superconducting condensate.
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14
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Wang X, Liu Y, Chen X, Zhang P, Liu X. Prediction of a novel robust superconducting state in TaS2 under high pressure. Phys Chem Chem Phys 2020; 22:8827-8833. [DOI: 10.1039/d0cp00838a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A novel superconducting I4/mmm phase has been predicted in TaS2 under high pressure, illustrating an unusual superconductor–metal–superconductor transition.
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Affiliation(s)
- Xiaojun Wang
- School of Physics and Physical Engineering
- Qufu Normal University
- Qufu
- China
| | - Yunxian Liu
- School of Physics and Physical Engineering
- Qufu Normal University
- Qufu
- China
| | - Xin Chen
- School of Physics and Physical Engineering
- Qufu Normal University
- Qufu
- China
| | - Ping Zhang
- School of Physics and Physical Engineering
- Qufu Normal University
- Qufu
- China
| | - Xiaobing Liu
- School of Physics and Physical Engineering
- Qufu Normal University
- Qufu
- China
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