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Valence-skipping and quasi-two-dimensionality of superconductivity in a van der Waals insulator. Nat Commun 2022; 13:6938. [DOI: 10.1038/s41467-022-34726-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 11/01/2022] [Indexed: 11/15/2022] Open
Abstract
AbstractValence fluctuation of interacting electrons plays a crucial role in emergent quantum phenomena in correlated electron systems. The theoretical rationale is that this effect can drive a band insulator into a superconductor through charge redistribution around the Fermi level. However, the root cause of such a fluctuating leap in the ionic valency remains elusive. Here, we demonstrate a valence-skipping-driven insulator-to-superconductor transition and realize quasi-two-dimensional superconductivity in a van der Waals insulator GeP under pressure. This is shown to result from valence skipping of the Ge cation, altering its average valency from 3+ to 4+, turning GeP from a layered compound to a three-dimensional covalent system with superconducting critical temperature reaching its maximum of 10 K. Such a valence-skipping-induced superconductivity with a quasi-two-dimensional nature in thin samples, showing a Berezinskii-Kosterlitz-Thouless-like character, is further confirmed by angle-dependent upper-critical-field measurements. These findings provide a model system to examine competing order parameters in valence-skipping systems.
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Moca CP, Chirla R, Dóra B, Zaránd G. Quantum Criticality and Formation of a Singular Fermi Liquid in the Attractive SU(N>2) Anderson Model. PHYSICAL REVIEW LETTERS 2019; 123:136803. [PMID: 31697511 DOI: 10.1103/physrevlett.123.136803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 08/12/2019] [Indexed: 06/10/2023]
Abstract
While much is known about repulsive quantum impurity models, significantly less attention has been devoted to their attractive counterparts. This motivated us to study the attractive SU(N) Anderson impurity model. While for the repulsive case the phase diagram features mild N dependence and the ground state is always a Fermi liquid, in the attractive case a Kosterlitz-Thouless charge localization phase transition is revealed for N>2. Beyond a critical value of attractive interaction, an abrupt jump appears in the number of particles at the impurity site, and a singular Fermi liquid state emerges, where the scattering of quasiparticles is found to exhibit power law behavior with fractional power. The capacity diverges exponentially at the quantum critical point, signaling the Kosterlitz-Thouless transition.
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Affiliation(s)
- Cătălin Paşcu Moca
- BME-MTA Exotic Quantum Phases Research Group, Institute of Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111 Budapest, Hungary
- Department of Physics, University of Oradea, 410087 Oradea, Romania
| | - Razvan Chirla
- Department of Physics, University of Oradea, 410087 Oradea, Romania
- School of Medicine and Pharmacy, University of Oradea, 410087 Oradea, Romania
| | - Balázs Dóra
- Department of Theoretical Physics and MTA-BME Lendület Topology and Correlation Research Group, Budapest University of Technology and Economics, 1521 Budapest, Hungary
| | - Gergely Zaránd
- BME-MTA Exotic Quantum Phases Research Group, Institute of Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111 Budapest, Hungary
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Thermoelectrics of Interacting Nanosystems—Exploiting Superselection Instead of Time-Reversal Symmetry. ENTROPY 2017. [DOI: 10.3390/e19120668] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Dramatically Enhanced Superconductivity in Elemental Bismuth from Excitonic Fluctuation Exchange. Sci Rep 2017; 7:10993. [PMID: 28887558 PMCID: PMC5591209 DOI: 10.1038/s41598-017-11269-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Accepted: 08/04/2017] [Indexed: 11/18/2022] Open
Abstract
Motivated by the remarkable discovery of superconductivity in elemental Bismuth at ambient pressure, we study its normal state in detail using a combination of tight-binding (TB) band-structure supplemented by dynamical mean-field theory (DMFT). We show that a two-fluid model composed of preformed and dynamically fluctuating excitons coupled to a tiny number of carriers provides a unified rationalization of a range of ill-understood normal state spectral and transport data. Based on these, we propose that resonant scattering involving a very low density of renormalized carriers and the excitonic liquid drives logarithmic enhancement of vertex corrections, boosting superconductivity in Bi. A confirmatory test for our proposal would be the experimental verification of an excitonic semiconductor with electronic nematicity as a ‘competing order’ on inducing a semi-metal-to semiconductor transition in Bi by an external perturbation like pressure
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Prawiroatmodjo GEDK, Leijnse M, Trier F, Chen Y, Christensen DV, von Soosten M, Pryds N, Jespersen TS. Transport and excitations in a negative-U quantum dot at the LaAlO 3/SrTiO 3 interface. Nat Commun 2017; 8:395. [PMID: 28855569 PMCID: PMC5577219 DOI: 10.1038/s41467-017-00495-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Accepted: 07/03/2017] [Indexed: 11/20/2022] Open
Abstract
In a solid-state host, attractive electron-electron interactions can lead to the formation of local electron pairs which play an important role in the understanding of prominent phenomena such as high T c superconductivity and the pseudogap phase. Recently, evidence of a paired ground state without superconductivity was demonstrated at the level of single electrons in quantum dots at the interface of LaAlO3 and SrTiO3. Here, we present a detailed study of the excitation spectrum and transport processes of a gate-defined LaAlO3/SrTiO3 quantum dot exhibiting pairing at low temperatures. For weak tunneling, the spectrum agrees with calculations based on the Anderson model with a negative effective charging energy U, and exhibits an energy gap corresponding to the Zeeman energy of the magnetic pair-breaking field. In contrast, for strong coupling, low-bias conductance is enhanced with a characteristic dependence on temperature, magnetic field and chemical potential consistent with the charge Kondo effect.Complex oxide devices provide a platform for studying and making use of strongly correlated electronic behavior. Here the authors present a LaAlO3/SrTiO3 quantum dot and show that its transport behavior is consistent with the presence of attractive electron interactions and the charge Kondo effect.
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Affiliation(s)
- Guenevere E D K Prawiroatmodjo
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark
| | - Martin Leijnse
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark
- Division of Solid State Physics and NanoLund, Lund University, Box 118, SE-221 00, Lund, Sweden
| | - Felix Trier
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark
- Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, 4000, Roskilde, Denmark
| | - Yunzhong Chen
- Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, 4000, Roskilde, Denmark
| | - Dennis V Christensen
- Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, 4000, Roskilde, Denmark
| | - Merlin von Soosten
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark
- Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, 4000, Roskilde, Denmark
| | - Nini Pryds
- Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, 4000, Roskilde, Denmark
| | - Thomas S Jespersen
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark.
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Yoo G, Park J, Lee SSB, Sim HS. Anisotropic charge Kondo effect in a triple quantum dot. PHYSICAL REVIEW LETTERS 2014; 113:236601. [PMID: 25526143 DOI: 10.1103/physrevlett.113.236601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Indexed: 06/04/2023]
Abstract
We predict that an anisotropic charge Kondo effect appears in a triple quantum dot, when the system has twofold degenerate ground states of (1,1,0) and (0,0,1) charge configurations. Using bosonization and refermionization methods, we find that at low temperature the system has the two different phases of massive charge fluctuations between the two charge configurations and vanishing fluctuations, which are equivalent with the Kondo-screened and ferromagnetic phases of the anisotropic Kondo model, respectively. The phase transition is identifiable by electron conductance measurement, offering the possibility of experimentally exploring the anisotropic Kondo model. Our charge Kondo effect has a similar origin to that in a negative-U Anderson impurity.
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Affiliation(s)
- Gwangsu Yoo
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
| | - Jinhong Park
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
| | - S-S B Lee
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
| | - H-S Sim
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
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Costi TA, Zlatić V. Charge Kondo anomalies in PbTe doped with Tl impurities. PHYSICAL REVIEW LETTERS 2012; 108:036402. [PMID: 22400764 DOI: 10.1103/physrevlett.108.036402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Indexed: 05/31/2023]
Abstract
We investigate the properties of PbTe doped with a small concentration x of Tl impurities acting as acceptors and described by Anderson impurities with negative onsite correlation energy. We use the numerical renormalization group method to show that the resulting charge Kondo effect naturally accounts for the unusual low temperature and doping dependence of normal state properties, including the self-compensation effect in the carrier density and the nonmagnetic Kondo anomaly in the resistivity. These are found to be in good qualitative agreement with experiment. Our results for the Tl s-electron spectral function provide a new interpretation of point contact data.
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Affiliation(s)
- T A Costi
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
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Dubi Y, Balatsky AV. Impurity-induced bound states and proximity effect in a bilayer exciton condensate. PHYSICAL REVIEW LETTERS 2010; 104:166802. [PMID: 20482072 DOI: 10.1103/physrevlett.104.166802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Indexed: 05/29/2023]
Abstract
The effect of impurities which induce local interlayer tunneling in bilayer exciton condensates is discussed. We show that a localized single-fermion bound state emerges inside the gap for any strength of impurity scattering and calculate the dependence of the impurity state energy and wave function on the potential strength. We show that such an impurity-induced single-fermion state enhances the interlayer coherence around it, and is similar to the superconducting proximity effect. As a direct consequence of these single-impurity states, we predict that a finite concentration of such impurities will increase the critical temperature for exciton condensation.
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Affiliation(s)
- Yonatan Dubi
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Nakayama K, Sato T, Takahashi T, Murakami H. Doping induced evolution of Fermi surface in low carrier superconductor Tl-doped PbTe. PHYSICAL REVIEW LETTERS 2008; 100:227004. [PMID: 18643449 DOI: 10.1103/physrevlett.100.227004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2007] [Indexed: 05/26/2023]
Abstract
We have performed high-resolution angle-resolved photoemission spectroscopy on Tl-doped PbTe. We observed a distinct energy shift of the valence band and core levels upon Tl doping, together with the evolution of a small hole pocket around the X[over] point in the Brillouin zone, while no clear evidence for the localized states near the Fermi level is observed. These experimental results suggest that direct hole doping into the valence band and resultant emergence of a small Fermi surface are responsible for the metallic conductivity in Tl-doped PbTe.
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Affiliation(s)
- K Nakayama
- Department of Physics, Tohoku University, Sendai 980-8578, Japan
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Koch J, Raikh ME, von Oppen F. Pair Tunneling through Single Molecules. PHYSICAL REVIEW LETTERS 2006; 96:056803. [PMID: 16486970 DOI: 10.1103/physrevlett.96.056803] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2005] [Indexed: 05/06/2023]
Abstract
By a polaronic energy shift, the effective charging energy of molecules can become negative, favoring ground states with even numbers of electrons. Here we show that charge transport through such molecules near ground-state degeneracies is dominated by tunneling of electron pairs which coexists with (featureless) single-electron cotunneling. Because of the restricted phase space for pair tunneling, the current-voltage characteristics exhibit striking differences from the conventional Coulomb blockade. In asymmetric junctions, pair tunneling can be used for gate-controlled current rectification and switching.
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Affiliation(s)
- Jens Koch
- Institut für Theoretische Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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Matsushita Y, Bluhm H, Geballe TH, Fisher IR. Evidence for charge Kondo effect in superconducting Tl-doped PbTe. PHYSICAL REVIEW LETTERS 2005; 94:157002. [PMID: 15904175 DOI: 10.1103/physrevlett.94.157002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2004] [Indexed: 05/02/2023]
Abstract
We report results of low-temperature thermodynamic and transport measurements of Pb1-xTlxTe single crystals for Tl concentrations up to the solubility limit of approximately x=1.5%. For all doped samples, we observe a low-temperature resistivity upturn that scales in magnitude with the Tl concentration. The temperature and field dependence of this upturn are consistent with a charge Kondo effect involving degenerate Tl valence states differing by two electrons, with a characteristic Kondo temperature T(K) approximately 6 K. The observation of such an effect supports an electronic pairing mechanism for superconductivity in this material and may account for the anomalously high T(c) values.
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Affiliation(s)
- Y Matsushita
- Department of Materials Science and Engineering and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305-4045, USA
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Dzero M, Schmalian J. Superconductivity in charge Kondo systems. PHYSICAL REVIEW LETTERS 2005; 94:157003. [PMID: 15904176 DOI: 10.1103/physrevlett.94.157003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2004] [Indexed: 05/02/2023]
Abstract
We present a theory for superconductivity and charge Kondo fluctuations, i.e., resonant quantum valence fluctuations by two charge units, for Tl-doped PbTe. We show that Tl is very special as it first supplies a certain amount of charge carriers to the PbTe-valence band and then puts itself into a self-tuned resonant state to yield a new, robust pairing mechanism for these carriers.
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Affiliation(s)
- Maxim Dzero
- Department of Physics and Astronomy and Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
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Taraphder A, Krishnamurthy HR, Pandit R, Ramakrishnan TV. Negative-U extended Hubbard model for doped barium bismuthates. PHYSICAL REVIEW. B, CONDENSED MATTER 1995; 52:1368-1388. [PMID: 9980720 DOI: 10.1103/physrevb.52.1368] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Perakis IE, Varma CM. Non-Fermi-liquid states of a magnetic ion in a metal: Particle-hole symmetric case. PHYSICAL REVIEW. B, CONDENSED MATTER 1994; 49:9041-9051. [PMID: 10009683 DOI: 10.1103/physrevb.49.9041] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Mooij JE. Localized superconductivity. PHYSICAL REVIEW. B, CONDENSED MATTER 1992; 45:9940-9950. [PMID: 10000885 DOI: 10.1103/physrevb.45.9940] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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