Tunneling density of states in cuprate and bismuthate superconductors

Zasadzinski, J. F.; Tralshawala, N.; Romano, P.; Huang, Qiang; Chen, Jun; Gray, K. E.

doi:10.1016/0022-3697(92)90154-6

Cited by 43 publications

(18 citation statements)

References 9 publications

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“…An enhanced, symmetric dip feature in the conductance is found at approximately 3D in superconductorinsulator-superconductor (SIS) junctions [11], which can be probed with our PCT techniques [3]. This is consistent with a dip at ϳ2D, in a d-wave DOS [9] because features are shifted by an additional factor of D in the SIS configuration.…”

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confidence: 61%

“…There have been numerous SIN tunneling studies of Bi2212 including STM [10] and PCT [1,3] which displayed a spectral feature (dip or shoulder) at a voltage approximately twice that of the conductance peak ͑eV ϳ 2D͒. An enhanced, symmetric dip feature in the conductance is found at approximately 3D in superconductorinsulator-superconductor (SIS) junctions [11], which can be probed with our PCT techniques [3].…”

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confidence: 96%

“…This is consistent with a dip at ϳ2D, in a d-wave DOS [9] because features are shifted by an additional factor of D in the SIS configuration. The enhanced size of the dip in SIS junctions as well as the symmetry are consequences of the convolution of the quasiparticle density of states with itself [3,9]. In a recent STM study [2] of Bi2212 it was argued that the dip feature was absent for voltage polarities corresponding to electron injection.…”

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confidence: 99%

“…[S0031-9007(97)04908-9] PACS numbers: 74.50. + r, 74.62.Dh, 74.72.Hs A provocative feature that has commonly been observed in the superconductor-insulator-normal (SIN) metal tunneling conductances of Bi 2 Sr 2 CaCu 2 O 81d (Bi2212) is a dip at jeV j ϳ 2D that is very large for voltage polarities which correspond to the removal of quasiparticles from the superconductor [1][2][3]. This feature has generated much interest due to its similarity to a dip found in the angle-resolved photoemission (ARPES) [4,5] spectra of Bi2212 and to strong-coupling effects in general [6].…”

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confidence: 99%

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Unusual Strong-Coupling Effects in the Tunneling Spectroscopy of Optimally Doped and OverdopedBi2Sr2CaCu2

et al. 1998

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Tunneling spectroscopy measurements are reported on single crystals of Bi 2 Sr 2 CaCu 2 O 81d using vacuum tunneling and point-contact methods. A reproducible dip feature in the tunneling conductance is found near jeV j 2D, observed for both voltage polarities in the best resolved spectra. With overdoping the position of the dip continues to scale with D, and its magnitude decreases as D decreases. These results indicate that the dip feature arises from a strong-coupling effect whereby the quasiparticle lifetime is decreased at a characteristic energy of ϳ2D, consistent with an electron-electron pairing interaction. [S0031-9007(97)04908-9] PACS numbers: 74.50. + r, 74.62.Dh, 74.72.Hs A provocative feature that has commonly been observed in the superconductor-insulator-normal (SIN) metal tunneling conductances of Bi 2 Sr 2 CaCu 2 O 81d (Bi2212) is a dip at jeV j ϳ 2D that is very large for voltage polarities which correspond to the removal of quasiparticles from the superconductor [1][2][3]. This feature has generated much interest due to its similarity to a dip found in the angle-resolved photoemission (ARPES) [4,5] spectra of Bi2212 and to strong-coupling effects in general [6]. But in contrast to the tunneling phonon structures observed in strong-coupled, low-T c superconductors [6], the dip is often highly asymmetric with bias voltage. For voltages corresponding to electron injection, the dip has appeared as a shoulder in early point-contact tunneling (PCT) measurements [1] and is scarcely observable in some scanning tunneling microscope (STM) measurements [2]. We report here that the dip feature is indeed observed for both bias voltage polarities in the best resolved SIN spectra obtained from both STM and PCT methods. This points toward a strong-coupling interpretation. As T c and D are reduced by overdoping (the latter from 37 to 15 meV in this study), the dip location continues to scale with D and its magnitude is reduced. The coupling to D is quite unusual and suggests that the dip arises from a pairing interaction that is purely electronic so that the superconducting gap feeds back into the excitations which mediate the pairing. This is also consistent with recent interpretations of the dip in ARPES spectra as arising from the coupling of quasiparticles to collective excitations [7,8].SIN tunneling spectroscopy is a unique probe of high temperature superconductors (HTS) in that it can, in principle, reveal the quasiparticle excitation spectrum directly with an energy resolution better than 1 meV. In conventional, s-wave superconductors, strong-coupling effects due to quasiparticle emission of bosons of frequency v produce a dip feature [6] in the tunneling conductance, dI͞dV , near a voltage, eV D 1 "v. More precisely, it is the maximum negative slope if dI͞dV vs V that pinpoints the boson frequency. In d-wave superconductors, which have gap nodes, quasiparticle decay processes which turn on at some threshold energy (e.g., 2D) display a dip in the density of states (DOS) near that energy [9], unshifted...

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confidence: 61%

mentioning

confidence: 96%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Unusual Strong-Coupling Effects in the Tunneling Spectroscopy of Optimally Doped and OverdopedBi2Sr2CaCu2

et al. 1998

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“…1 also shows that there is not any large degree of inhomogeneity in either the break junctions or c-axis mesa junctions as they agree with a local STS spectrum in a superconducting region. It has generally been noted [15,16] that the dip voltage scaled with the maximum d-wave gap, e.g. eV dip , 3D in SIS junctions as is evident in Fig.…”

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Aspects of the tunneling dip feature in Bi2Sr2CaCu2O8+ and its relation to the resonance spin excitation

Zasadzinski

Özyüzer

Miyakawa

et al. 2002

Journal of Physics and Chemistry of Solids

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Break-junction tunneling data are reported in Bi 2 Sr 2 CaCu 2 O 8þd over a wide range of hole concentration from underdoped to overdoped. The strong conductance peaks in the superconducting state reveal a single gap consistent with d-wave symmetry. In addition, sharp dips are observed at a voltage, V=e; measured with respect to the gap edge. These features are shown to be reproduced in other junction types from the literature including atomically resolved STM and c-axis mesas, establishing their intrinsic character. Trends are observed with doping and temperature which link the dip to the resonance spin excitation and indicate that the quasiparticles are strongly coupled to this mode. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Superconductors Fine structure in the tunneling spectra of conventional superconductors such as Pb or Nb reveals completely the nature of the electron -phonon interaction responsible for pairing and superconductivity [1]. For high T c cuprates, however, tunneling and other spectroscopies have not led to any consensus on the pairing mechanism. On the contrary, spectral features are currently being interpreted within radically different theoretical frameworks. One such feature is a suppression of spectral weight, more commonly termed the 'dip', which is observed in ARPES, tunneling and a.c. conductivity measurements and which has received considerable theoretical attention [2]. Interpretations of the dip in tunneling have ranged from it being described as an ordinary background effect to suggestions that it is a strongcoupling effect tied to the mechanism of superconductivity [3]. One way of removing such ambiguities is to examine how the dip evolves with thermodynamic variables such as temperature or hole concentration. Such trends might also serve to identify the origin of this and other spectral features.In this article, we examine a large set of superconductor -insulator -superconductor (SIS) tunneling data on Bi 2 Sr 2 CaCu 2 O 8þd (Bi2212) over a very wide doping range from underdoped ðT c ¼ 74 KÞ to optimal doped ðT c ¼ 95 KÞ to overdoped ðT c ¼ 48 KÞ: From zero bias up to the gap voltage, 2D=e; the measured conductances are close to that expected from the density of states (DOS) found in weak-coupling, mean-field models of a d-wave order parameter. In conjunction with the presence of Josephson currents, this suggests the gap is always of superconducting character. However, the conductances also reveal sharp dips at a voltage, V=e; beyond the gap edge. These dip features are similar to structures ascribed to phonons in conventional superconductors in that there appears to be a corresponding pile-up of states at the gap edge. This suggests that electrons are coupled to some type of collective excitation of energy , V. Recently, it has been shown that V extracted from the dip minima scales as 4:9kT c over the entire doping range [4] which is close to that of the resonance spin excitation energy, V res , found in neutron scattering [5 -7]. These data are d...

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Theories of Superconductivity

Saxena

2012

High-Temperature Superconductors

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Tunneling density of states in cuprate and bismuthate superconductors

Cited by 43 publications

References 9 publications

Unusual Strong-Coupling Effects in the Tunneling Spectroscopy of Optimally Doped and OverdopedBi2Sr2CaCu2

Unusual Strong-Coupling Effects in the Tunneling Spectroscopy of Optimally Doped and OverdopedBi2Sr2CaCu2

Aspects of the tunneling dip feature in Bi2Sr2CaCu2O8+ and its relation to the resonance spin excitation

Theories of Superconductivity

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