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Experimental evidence of anomalously large superconducting gap on topological surface state of β-Bi 2Pd film. Sci Bull (Beijing) 2019; 64:1215-1221. [PMID: 36659601 DOI: 10.1016/j.scib.2019.07.019] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 07/03/2019] [Accepted: 07/12/2019] [Indexed: 01/21/2023]
Abstract
Connate topological superconductor (TSC) combines topological surface states with nodeless superconductivity in a single material, achieving effective p-wave pairing without interface complication. By combining angle-resolved photoemission spectroscopy and in-situ molecular beam epitaxy, we studied the momentum-resolved superconductivity in β-Bi2Pd film. We found that the superconducting gap of topological surface state (ΔTSS ∼ 3.8 meV) is anomalously enhanced from its bulk value (Δb ∼ 0.8 meV). The ratio of 2ΔTSS/kBTc ∼ 16.3, is substantially larger than the BCS value. By measuring β-Bi2Pd bulk single crystal as a comparison, we clearly observed the upward-shift of chemical potential in the film. In addition, a concomitant increasing of surface weight on the topological surface state was revealed by our first principle calculation, suggesting that the Dirac-fermion-mediated parity mixing may cause this anomalous superconducting enhancement. Our results establish β-Bi2Pd film as a unique case of connate TSCs with a highly enhanced topological superconducting gap, which may stabilize Majorana zero modes at a higher temperature.
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Chatterjee U, Zhao J, Iavarone M, Di Capua R, Castellan JP, Karapetrov G, Malliakas CD, Kanatzidis MG, Claus H, Ruff JPC, Weber F, van Wezel J, Campuzano JC, Osborn R, Randeria M, Trivedi N, Norman MR, Rosenkranz S. Emergence of coherence in the charge-density wave state of 2H-NbSe2. Nat Commun 2015; 6:6313. [PMID: 25687135 PMCID: PMC4339883 DOI: 10.1038/ncomms7313] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Accepted: 01/19/2015] [Indexed: 12/02/2022] Open
Abstract
A charge-density wave (CDW) state has a broken symmetry described by a complex order parameter with an amplitude and a phase. The conventional view, based on clean, weak-coupling systems, is that a finite amplitude and long-range phase coherence set in simultaneously at the CDW transition temperature Tcdw. Here we investigate, using photoemission, X-ray scattering and scanning tunnelling microscopy, the canonical CDW compound 2H-NbSe2 intercalated with Mn and Co, and show that the conventional view is untenable. We find that, either at high temperature or at large intercalation, CDW order becomes short-ranged with a well-defined amplitude, which has impacts on the electronic dispersion, giving rise to an energy gap. The phase transition at Tcdw marks the onset of long-range order with global phase coherence, leading to sharp electronic excitations. Our observations emphasize the importance of phase fluctuations in strongly coupled CDW systems and provide insights into the significance of phase incoherence in ‘pseudogap’ states. Charge density waves are described by a complex order parameter whose amplitude is expected to vanish at the transition temperature. This study shows that the transition in 2H-NbSe2 is driven by fluctuations of the phase of the order parameter, with a finite amplitude surviving in the disordered state.
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Affiliation(s)
- U Chatterjee
- 1] Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA [2] Department of Physics, University of Virginia, Charlottesville, Virginia 22904, USA
| | - J Zhao
- 1] Department of Physics, University of Virginia, Charlottesville, Virginia 22904, USA [2] Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA
| | - M Iavarone
- Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA
| | - R Di Capua
- Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA
| | - J P Castellan
- 1] Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA [2] Institute of Solid State Physics, Karlsruhe Institute of Technology, PO Box 3640, D-76021 Karlsruhe, Germany
| | - G Karapetrov
- Department of Physics, Drexel University, Philadelphia, Pennsylvania 19104, USA
| | - C D Malliakas
- 1] Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA [2] Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| | - M G Kanatzidis
- 1] Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA [2] Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| | - H Claus
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - J P C Ruff
- 1] Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA [2] CHESS, Cornell University, Ithaca, New York 14853, USA
| | - F Weber
- 1] Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA [2] Institute of Solid State Physics, Karlsruhe Institute of Technology, PO Box 3640, D-76021 Karlsruhe, Germany
| | - J van Wezel
- 1] Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA [2] Institute for Theoretical Physics, University of Amsterdam, Tyndall Avenue, 1090 GL Amsterdam, The Netherlands
| | - J C Campuzano
- 1] Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA [2] Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA
| | - R Osborn
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - M Randeria
- Department of Physics, Ohio State University, Columbus, Ohio 43210, USA
| | - N Trivedi
- Department of Physics, Ohio State University, Columbus, Ohio 43210, USA
| | - M R Norman
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - S Rosenkranz
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
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Kondo T, Santander-Syro AF, Copie O, Liu C, Tillman ME, Mun ED, Schmalian J, Bud'ko SL, Tanatar MA, Canfield PC, Kaminski A. Momentum dependence of the superconducting gap in NdFeAsO0.9F0.1 single crystals measured by angle resolved photoemission spectroscopy. PHYSICAL REVIEW LETTERS 2008; 101:147003. [PMID: 18851561 DOI: 10.1103/physrevlett.101.147003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2008] [Indexed: 05/26/2023]
Abstract
We use angle resolved photoemission spectroscopy to study the momentum dependence of the superconducting gap in NdFeAsO0.9F0.1 single crystals. We find that the Gamma hole pocket is fully gapped below the superconducting transition temperature. The value of the superconducting gap is 15+/-1.5 meV and its anisotropy around the hole pocket is smaller than 20% of this value-consistent with an isotropic or anisotropic s-wave symmetry of the order parameter. This is a significant departure from the situation in the cuprates, pointing to the possibility that the superconductivity in the iron arsenic based system arises from a different mechanism.
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Affiliation(s)
- Takeshi Kondo
- Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
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Kanigel A, Chatterjee U, Randeria M, Norman MR, Koren G, Kadowaki K, Campuzano JC. Evidence for pairing above the transition temperature of cuprate superconductors from the electronic dispersion in the pseudogap phase. PHYSICAL REVIEW LETTERS 2008; 101:137002. [PMID: 18851483 DOI: 10.1103/physrevlett.101.137002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2008] [Indexed: 05/26/2023]
Abstract
In the underdoped high temperature superconductors, instead of a complete Fermi surface above Tc, only disconnected Fermi arcs appear, separated by regions that still exhibit an energy gap. We show that in this pseudogap phase, the energy-momentum relation of electronic excitations near EF behaves like the dispersion of a normal metal on the Fermi arcs, but like that of a superconductor in the gapped regions. We argue that this dichotomy in the dispersion is difficult to reconcile with a competing order parameter, but is consistent with pairing without condensation.
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Affiliation(s)
- A Kanigel
- Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA
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Wilson JA. Evolution with hole doping of the electronic excitation spectrum in the cuprate superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:385210. [PMID: 21693828 DOI: 10.1088/0953-8984/20/38/385210] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The recent scanning tunnelling results of Alldredge and co-workers on Bi-2212 and of Hanaguri and co-workers on Na-CCOC (Ca(2-x)Na(x)CuO(2)Cl(2)) are examined from the perspective of the Bardeen-Cooper-Schrieffer (BCS)/Bose-Einstein condensation boson-fermion resonant crossover model for the mixed-valence high temperature superconductor (HTSC) cuprates. The model specifies the two energy scales controlling the development of HTSC behaviour and the dichotomy often now alluded to between nodal and antinodal phenomena in the HTSC cuprates. An indication is extracted from the data as to how the choice of the particular HTSC system sees these two basic energy scales ([Formula: see text], the local pair binding energy, and Δ(sc), the nodal BCS-like gap parameter) evolve with doping and change in the degree of metallization of the structurally and electronically perturbed mixed-valent environment.
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Affiliation(s)
- John A Wilson
- H H Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK
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Sensarma R, Randeria M, Trivedi N. Can one determine the underlying fermi surface in the superconducting state of strongly correlated systems? PHYSICAL REVIEW LETTERS 2007; 98:027004. [PMID: 17358639 DOI: 10.1103/physrevlett.98.027004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2006] [Indexed: 05/14/2023]
Abstract
The question of determining the underlying Fermi surface (FS) that is gapped by superconductivity (SC) is of central importance in strongly correlated systems, particularly in view of angle-resolved photoemission experiments. Here we explore various definitions of the FS in the superconducting state using the zero-energy Green's function, the excitation spectrum, and the momentum distribution. We examine (a) d-wave SC in high-Tc cuprates, and (b) the s-wave superfluid in the BCS-Bose-Einstein condensation (BEC) crossover. In each case we show that the various definitions agree, to a large extent, but all of them violate the Luttinger count and do not enclose the total electron density. We discuss the important role of chemical potential renormalization and incoherent spectral weight in this violation.
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Affiliation(s)
- Rajdeep Sensarma
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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Gros C, Edegger B, Muthukumar VN, Anderson PW. Determining the underlying Fermi surface of strongly correlated superconductors. Proc Natl Acad Sci U S A 2006; 103:14298-301. [PMID: 16983075 PMCID: PMC1599958 DOI: 10.1073/pnas.0606219103] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The notion of a Fermi surface (FS) is one of the most ingenious concepts developed by solid-state physicists during the past century. It plays a central role in our understanding of interacting electron systems. Extraordinary efforts have been undertaken, by both experiment and theory, to reveal the FS of the high-temperature superconductors, the most prominent class of strongly correlated superconductors. Here, we discuss some of the prevalent methods used to determine the FS and show that they generally lead to erroneous results close to half-filling and at low temperatures, because of the large superconducting gap (pseudogap) below (above) the superconducting transition temperature. Our findings provide a perspective on the interplay between strong correlations and superconductivity and highlight the importance of strong coupling theories for the characterization and determination of the underlying FS in angle-resolved photoemission spectroscopy experiments.
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Affiliation(s)
- Claudius Gros
- *Institute for Theoretical Physics, J. W. Goethe University, 60438 Frankfurt, Germany
| | - Bernhard Edegger
- *Institute for Theoretical Physics, J. W. Goethe University, 60438 Frankfurt, Germany
- Department of Physics, City College of the City University of New York, New York, NY 10031; and
- Department of Physics, Princeton University, Princeton, NJ 08544
| | - V. N. Muthukumar
- Department of Physics, City College of the City University of New York, New York, NY 10031; and
| | - P. W. Anderson
- Department of Physics, Princeton University, Princeton, NJ 08544
- To whom correspondence should be addressed. E-mail:
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McElroy K, Simmonds RW, Hoffman JE, Lee DH, Orenstein J, Eisaki H, Uchida S, Davis JC. Relating atomic-scale electronic phenomena to wave-like quasiparticle states in superconducting Bi2Sr2CaCu2O8+delta. Nature 2003; 422:592-6. [PMID: 12686994 DOI: 10.1038/nature01496] [Citation(s) in RCA: 398] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2002] [Accepted: 02/14/2003] [Indexed: 11/09/2022]
Abstract
The electronic structure of simple crystalline solids can be completely described in terms either of local quantum states in real space (r-space), or of wave-like states defined in momentum-space (k-space). However, in the copper oxide superconductors, neither of these descriptions alone may be sufficient. Indeed, comparisons between r-space and k-space studies of Bi2Sr2CaCu2O8+delta (Bi-2212) reveal numerous unexplained phenomena and apparent contradictions. Here, to explore these issues, we report Fourier transform studies of atomic-scale spatial modulations in the Bi-2212 density of states. When analysed as arising from quasiparticle interference, the modulations yield elements of the Fermi-surface and energy gap in agreement with photoemission experiments. The consistency of numerous sets of dispersing modulations with the quasiparticle interference model shows that no additional order parameter is required. We also explore the momentum-space structure of the unoccupied states that are inaccessible to photoemission, and find strong similarities to the structure of the occupied states. The copper oxide quasiparticles therefore apparently exhibit particle-hole mixing similar to that of conventional superconductors. Near the energy gap maximum, the modulations become intense, commensurate with the crystal, and bounded by nanometre-scale domains. Scattering of the antinodal quasiparticles is therefore strongly influenced by nanometre-scale disorder.
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Affiliation(s)
- K McElroy
- Department of Physics, University of California, and Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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