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Nanoscale Phase Separation of Incommensurate and Quasi-Commensurate Spin Stripes in Low Temperature Spin Glass of La2−xSrxNiO4. CONDENSED MATTER 2021. [DOI: 10.3390/condmat6040045] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
While spin striped phases in La2−xSrxNiO4+y for 0.25 < x < 0.33 are the archetypal case of a 1D spin density wave (SDW) phase in doped antiferromagnetic strongly correlated perovskites, few information is available on the SDW spatial organization. In this context, we have measured the spatial variation of the wave vector of the SDW reflection profile by scanning micro X-ray diffractions with a coherent beam. We obtained evidence of a SDW order–disorder transition by lowering a high temperature phase (T > 50 K) to a low temperature phase (T < 50 K). We have identified quasi-commensurate spin stripe puddles in the ordered phase at 50 < T < 70 K, while the low temperature spin glassy phase presents a nanoscale phase separation of T = 30 K, with the coexistence of quasi-commensurate and incommensurate spin stripe puddles assigned to the interplay of quantum frustration and strong electronic correlations.
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Abstract
The basic features of multi-band superconductivity and its implications are derived. In particular, it is shown that enhancements of the superconducting transition temperature take place due to interband interactions. In addition, isotope effects differ substantially from the typical BCS scheme as soon as polaronic coupling effects are present. Special cases of the model are polaronic coupling in one band as realized e.g., in cuprates, coexistence of a flat band and a steep band like in MgB2, crossovers between extreme cases. The advantages of the multiband approach as compared to the single band BCS model are elucidated and its rather frequent realization in actual systems discussed.
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Multiple Electronic Components and Lifshitz Transitions by Oxygen Wires Formation in Layered Cuprates and Nickelates. CONDENSED MATTER 2019. [DOI: 10.3390/condmat4010015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
There is growing compelling experimental evidence that a quantum complex matter scenario made of multiple electronic components and competing quantum phases is needed to grab the key physics of high critical temperature ( T c ) superconductivity in layered cuprates. While it is known that defect self-organization controls T c , the mechanism remains an open issue. Here we focus on the theoretical prediction of the multiband electronic structure and the formation of broken Fermi surfaces generated by the self-organization of oxygen interstitials O i atomic wires in the spacer layers in HgBa 2 CuO 4 ± δ , La 2 CuO 4 ± δ and La 2 NiO 4 ± δ , by means of self-consistent Linear Muffin-Tin Orbital (LMTO) calculations. The electronic structure of a first phase of ordered O i atomic wires and of a second glassy phase made of disordered O i impurities have been studied through supercell calculations. We show the common features of the influence of O i wires in the electronic structure in three types of materials. The ordering of O i into wires leads to a separation of the electronic states between the O i ensemble and the rest of the bulk. The wire formation first produces quantum confined localized states near the wire, which coexist with, Second, delocalized states in the Fermi surface (FS) of doped cuprates. A new scenario emerges for high T c superconductivity, where Kitaev wires with Majorana bound states are proximity-coupled to a 2D d-wave superconductor.
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The Road Map toward Room-Temperature Superconductivity: Manipulating Different Pairing Channels in Systems Composed of Multiple Electronic Components. CONDENSED MATTER 2017. [DOI: 10.3390/condmat2030024] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Breakdown of the Migdal approximation at Lifshitz transitions with giant zero-point motion in the H3S superconductor. Sci Rep 2016; 6:24816. [PMID: 27095368 PMCID: PMC4837402 DOI: 10.1038/srep24816] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 04/06/2016] [Indexed: 11/18/2022] Open
Abstract
While 203 K high temperature superconductivity in H3S has been interpreted by BCS theory in the dirty limit here we focus on the effects of hydrogen zero-point-motion and the multiband electronic structure relevant for multigap superconductivity near Lifshitz transitions. We describe how the topology of the Fermi surfaces evolves with pressure giving different Lifshitz-transitions. A neck-disrupting Lifshitz-transition (type 2) occurs where the van Hove singularity, vHs, crosses the chemical potential at 210 GPa and new small 2D Fermi surface portions appear with slow Fermi velocity where the Migdal-approximation becomes questionable. We show that the neglected hydrogen zero-point motion ZPM, plays a key role at Lifshitz transitions. It induces an energy shift of about 600 meV of the vHs. The other Lifshitz-transition (of type 1) for the appearing of a new Fermi surface occurs at 130 GPa where new Fermi surfaces appear at the Γ point of the Brillouin zone here the Migdal-approximation breaks down and the zero-point-motion induces large fluctuations. The maximum Tc = 203 K occurs at 160 GPa where EF/ω0 = 1 in the small Fermi surface pocket at Γ. A Feshbach-like resonance between a possible BEC-BCS condensate at Γ and the BCS condensate in different k-space spots is proposed.
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Yang Y, Fedorov G, Shafranjuk SE, Klapwijk TM, Cooper BK, Lewis RM, Lobb CJ, Barbara P. Electronic Transport and Possible Superconductivity at Van Hove Singularities in Carbon Nanotubes. NANO LETTERS 2015; 15:7859-7866. [PMID: 26506109 DOI: 10.1021/acs.nanolett.5b02564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Van Hove singularities (VHSs) are a hallmark of reduced dimensionality, leading to a divergent density of states in one and two dimensions and predictions of new electronic properties when the Fermi energy is close to these divergences. In carbon nanotubes, VHSs mark the onset of new subbands. They are elusive in standard electronic transport characterization measurements because they do not typically appear as notable features and therefore their effect on the nanotube conductance is largely unexplored. Here we report conductance measurements of carbon nanotubes where VHSs are clearly revealed by interference patterns of the electronic wave functions, showing both a sharp increase of quantum capacitance, and a sharp reduction of energy level spacing, consistent with an upsurge of density of states. At VHSs, we also measure an anomalous increase of conductance below a temperature of about 30 K. We argue that this transport feature is consistent with the formation of Cooper pairs in the nanotube.
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Affiliation(s)
- Y Yang
- Department of Physics, Georgetown University , Washington, District of Columbia 20057, United States
| | - G Fedorov
- Department of Physics, Georgetown University , Washington, District of Columbia 20057, United States
| | - S E Shafranjuk
- Department of Physics and Astronomy, Northwestern University , Evanston, Illinois 60208, United States
| | - T M Klapwijk
- Kavli Institute of Nanoscience, Delft University of Technology , 2600 GA Delft, The Netherlands
- Laboratory for Quantum Limited Devices, Physics Department, Moscow State Pedagogical University , 29 Malaya Pirogovskaya Street, Moscow, 119992, Russia
| | - B K Cooper
- Kavli Institute of Nanoscience, Delft University of Technology , 2600 GA Delft, The Netherlands
| | - R M Lewis
- Department of Physics, CNAM, and JQI , University of Maryland , College Park, Maryland 20742, United States
| | - C J Lobb
- Department of Physics, CNAM, and JQI , University of Maryland , College Park, Maryland 20742, United States
| | - P Barbara
- Department of Physics, Georgetown University , Washington, District of Columbia 20057, United States
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Conradson SD, Gilbertson SM, Daifuku SL, Kehl JA, Durakiewicz T, Andersson DA, Bishop AR, Byler DD, Maldonado P, Oppeneer PM, Valdez JA, Neidig ML, Rodriguez G. Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation. Sci Rep 2015; 5:15278. [PMID: 26472071 PMCID: PMC4607891 DOI: 10.1038/srep15278] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 09/21/2015] [Indexed: 11/23/2022] Open
Abstract
Bose-Einstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photo- and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. That some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novel mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. A macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields.
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Affiliation(s)
- Steven D Conradson
- Synchrotron Soleil, L'Orme des Merisiers Saint-Aubin, BP 48 91192, Gif-sur-Yvette, France
| | | | | | - Jeffrey A Kehl
- Department of Chemistry, University of Rochester, NY 14627, USA
| | - Tomasz Durakiewicz
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | - David A Andersson
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | - Alan R Bishop
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | - Darrin D Byler
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | - Pablo Maldonado
- Department of Physics and Astronomy, Uppsala University, S-75120, Uppsala, Sweden
| | - Peter M Oppeneer
- Department of Physics and Astronomy, Uppsala University, S-75120, Uppsala, Sweden
| | - James A Valdez
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | | | - George Rodriguez
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
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Bianconi A, Jarlborg T. Lifshitz transitions and zero point lattice fluctuations in sulfur hydride showing near room temperature superconductivity. ACTA ACUST UNITED AC 2015. [DOI: 10.1515/nsm-2015-0006] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractEmerets’s experiments on pressurized sulfur hydride have shown that H3S metal has the highest known superconducting critical temperature Tc = 203 K. The Emerets data show pressure induced changes of the isotope coefficient between 0.25 and 0.5, in disagreement with Eliashberg theory which predicts a nearly constant isotope coefficient.We assign the pressure dependent isotope coefficient to Lifshitz transitions induced by pressure and zero point lattice fluctuations. It is known that pressure could induce changes of the topology of the Fermi surface, called Lifshitz transitions, but were neglected in previous papers on the H3S superconductivity issue. Here we propose thatH3S is a multi-gap superconductor with a first condensate in the BCS regime (located in the large Fermi surface with high Fermi energy) which coexists with second condensates in the BCS-BEC crossover regime (located on the Fermi surface spots with small Fermi energy) near the and Mpoints.We discuss the Bianconi-Perali-Valletta (BPV) superconductivity theory to understand superconductivity in H3S since the BPV theory includes the corrections of the chemical potential due to pairing and the configuration interaction between different condensates, neglected by the Eliashberg theory. These two terms in the BPV theory give the shape resonance in superconducting gaps, similar to Feshbach resonance in ultracold fermionic gases, which is known to amplify the critical temperature. Therefore this work provides some key tools useful in the search for new room temperature superconductors.
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Ideta S, Yoshida T, Nishi I, Fujimori A, Kotani Y, Ono K, Nakashima Y, Yamaichi S, Sasagawa T, Nakajima M, Kihou K, Tomioka Y, Lee CH, Iyo A, Eisaki H, Ito T, Uchida S, Arita R. Dependence of carrier doping on the impurity potential in transition-metal-substituted FeAs-based superconductors. PHYSICAL REVIEW LETTERS 2013; 110:107007. [PMID: 23521287 DOI: 10.1103/physrevlett.110.107007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Revised: 01/14/2013] [Indexed: 06/01/2023]
Abstract
In order to examine to what extent the rigid-band-like electron doping scenario is applicable to the transition metal-substituted Fe-based superconductors, we have performed angle-resolved photoemission spectroscopy studies of Ba(Fe(1-x)Ni(x))(2)As(2) (Ni-122) and Ba(Fe(1-x)Cu(x))(2)As(2) (Cu-122), and compared the results with Ba(Fe(1-x)Co(x))(2)As(2) (Co-122). We find that Ni 3d-derived features are formed below the Fe 3d band and that Cu 3d-derived ones further below it. The electron and hole Fermi surface (FS) volumes are found to increase and decrease with substitution, respectively, qualitatively consistent with the rigid-band model. However, the total extra electron number estimated from the FS volumes (the total electron FS volume minus the total hole FS volume) is found to decrease in going from Co-, Ni-, to Cu-122 for a fixed nominal extra electron number, that is, the number of electrons that participate in the formation of FS decreases with increasing impurity potential. We find that the Néel temperature T(N) and the critical temperature T(c) maximum are determined by the FS volumes rather than the nominal extra electron concentration or the substituted atom concentration.
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Affiliation(s)
- S Ideta
- Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
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