Josephson effect and single-particle tunneling in YBa2Cu3O7−x and YbBa2Cu3O7−x single-crystal break junctions

Ponomarev, Ya. G.; Aminov, B. A.; Hein, Matthias; Heinrichs, H.; Kresin, Vladimir Z.; Müller, Günter; Piel, H.; Rosner, K.; Tchesnokov, S. N.; Tsokur, E. B.; Wehler, D.; Winzer, Klaus; Yarygin, A. V.; Yusupov, Khabib

doi:10.1016/0921-4534(94)02452-9

Cited by 35 publications

(7 citation statements)

References 49 publications

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“…It was argued that single-particle tunneling experiments along the CuO 2 planes can probe the bulk electronic density of states since the mean-free path is far larger than the thickness of the possibly degraded surface layer. 28 Figure 2 ͑BTK͒ theory. 29 In this model, two parameters are introduced to describe the effective potential barrier ͑Z͒ and the superconducting energy gap ⌬.…”

mentioning

confidence: 99%

Nearly isotropics-wave gap in the bulk of the optimally electron-doped superconductorNd1.85Ce0.15
Zhao
¹

2010
Phys. Rev. B
17
2
12
0
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We address an important issue as to whether bulk-sensitive data of Raman scattering, optical conductivity, magnetic penetration depth, directional point-contact tunneling spectra, and nonmagnetic pair-breaking effect in optimally electron-doped Nd 1.85 Ce 0.15 CuO 4−y support a nodeless s-wave or d-wave superconducting gap. We numerically calculate Raman intensities, directional point-contact tunneling spectra, and nonmagnetic pairbreaking effect in terms of both s wave and d-wave gap symmetries. We find that all these bulk-sensitive data are in quantitative agreement with a nearly isotropic s-wave gap. The fact that T c is nearly independent of the residual resistivity rules out any d-wave gap symmetry.

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confidence: 99%

Nearly isotropics-wave gap in the bulk of the optimally electron-doped superconductorNd1.85Ce0.15
Zhao
¹

2010
Phys. Rev. B
17
2
12
0
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“…It is also shifted to lower energies. Some experiments 20 indicate a reduction in gap value with underdoping in YBCO while many experiments show an important increase in Bi2212. 19 Even if the gap is assumed to stay the same at 27 meV, the spin polarized neutron resonant frequency is known to decrease with doping.…”

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confidence: 99%

Coupling strength of charge carriers to spin fluctuations in high-temperature superconductors

Ćarbotte

Schachinger

Basov

1999

Nature

223

277

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In conventional superconductors, the most direct evidence of the mechanism responsible for superconductivity comes from tunnelling experiments, which provide a clear picture of the underlying electron-phonon interactions. As the coherence length in conventional superconductors is large, the tunnelling process probes several atomic layers into the bulk of the material; the observed structure in the current-voltage characteristics at the phonon energies gives, through inversion of the Eliashberg equations, the electron-phonon spectral density alpha2F(omega). The situation is different for the high-temperature copper oxide superconductors, where the coherence length (particularly for c-axis tunnelling) can be very short. Because of this, methods such as optical spectroscopy and neutron scattering provide a better route for investigating the underlying mechanism, as they probe bulk properties. Accurate reflection measurements at infrared wavelengths and precise polarized neutron-scattering data are now available for a variety of the copper oxides, and here we show that the conducting carriers (probed by infrared spectroscopy) are strongly coupled to a resonance structure in the spectrum of spin fluctuations (measured by neutron scattering). The coupling strength inferred from those results is sufficient to account for the high transition temperatures of the copper oxides, highlighting a prominent role for spin fluctuations in driving superconductivity in these materials.

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“…The contact area typical for Sm-1111, is about 10 − 30 nm, as estimated [33], thus providing local measurements of energy parameters. Intrinsic MARE (IMARE) similar to intrinsic Josephson effect [55] takes place in Andreev arrays and scales by a factor of m the position of any features caused by the bulk. In particular, SGS's would appear at bias voltages V n = 2m× ∆ L,S /en.…”

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confidence: 99%

Evidence of a multiple boson emission in Sm _1−x Th _x OFeAs

Kuzmichev

Kuzmicheva

Zhigadlo

2017

EPL

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-We studied a reproducible fine structure observed in dynamic conductance spectra of Andreev arrays in Sm1−xThxOFeAs superconductors with various thorium concentrations (x = 0.08-0.3) and critical temperatures Tc = 26-50 K. This structure is unambiguously caused by a multiple boson emission (of the same energy) during the process of multiple Andreev reflections. The directly determined energy of the bosonic mode reaches ε0 = 14.8 ± 2.2 meV for optimal compound. Within the studied range of Tc, this energy as well as the large ∆L and the small ∆S superconducting gaps, nearly scales with critical temperature with the characteristic ratio ε0/kBTc ≈ 3.2 (and 2∆L/kBTc ≈ 5.3, correspondingly) resembling the expected energy ∆L + ∆S of spin resonance and spectral density enhancement in s ± and s ++ states, respectively.Fe-based superconductors Sm 1−x Th x OFeAs belong to the oxypnictide family (so called 1111), and have rather simple crystal structure, resembling the stack of superconducting FeAs blocks alternating with Sm 1−x Th x O spacers along the c-direction [1]. Under electron doping, the T c varies in the wide range, reaching 54 K at x ≈ 0.3 nominal concentration [1,2]. Band-structure calculations [3] showed the density of states at the Fermi level formed mainly by iron 3d states. For this reason, the (Sm,Th) substitution affecting the spacer structure barely seems not changing the underlying pairing mechanism [4]. The Fermi surface consists of tubular sections, electron-like near the M point of the first Brillouin zone, and hole-like near the Γ point, both with no significant k z anisotropy [3,5].The majority of theoretical and experimental studies [3][4][5][6][7][8] suppose two superconducting condensates developing below T c . Earlier we reported the scaling between both gaps (∆ L -large gap, ∆ S -small gap) and T c , keeping 2∆ S /k B T c ≈ 1.2 − 1.6 and 2∆ L /k B T c = 5. 0−5.7 [4,9-11]. Similar 2∆ L /k B T c was obtained in literature for Sm-1111 in point-contact probes [12,13], and for various other 1111 [14][15][16][17][18][19][20]. Both BCS-ratios diverge from the weakcoupling BCS prediction due to a strong coupling in the "driving" bands where the large gap is developed, and a k-space proximity effect with the "driven" ∆ S bands. The pairing p-1

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Josephson effect and single-particle tunneling in YBa2Cu3O7−x and YbBa2Cu3O7−x single-crystal break junctions

Cited by 35 publications

References 49 publications

Nearly isotropics-wave gap in the bulk of the optimally electron-doped superconductorNd1.85Ce0.15
Zhao
¹

2010
Phys. Rev. B
17
2
12
0
View full text Add to dashboard Cite

Nearly isotropics-wave gap in the bulk of the optimally electron-doped superconductorNd1.85Ce0.15
Zhao
¹

2010
Phys. Rev. B
17
2
12
0
View full text Add to dashboard Cite

Coupling strength of charge carriers to spin fluctuations in high-temperature superconductors

Evidence of a multiple boson emission in Sm _1−x Th _x OFeAs

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Josephson effect and single-particle tunneling in YBa2Cu3O7−x and YbBa2Cu3O7−x single-crystal break junctions

Cited by 35 publications

References 49 publications

Nearly isotropics-wave gap in the bulk of the optimally electron-doped superconductorNd1.85Ce0.15Zhao1 2010Phys. Rev. B172120View full textAdd to dashboardCite

Nearly isotropics-wave gap in the bulk of the optimally electron-doped superconductorNd1.85Ce0.15Zhao1 2010Phys. Rev. B172120View full textAdd to dashboardCite

Coupling strength of charge carriers to spin fluctuations in high-temperature superconductors

Evidence of a multiple boson emission in Sm 1−x Th x OFeAs

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Product

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Nearly isotropics-wave gap in the bulk of the optimally electron-doped superconductorNd1.85Ce0.15
Zhao
¹

2010
Phys. Rev. B
17
2
12
0
View full text Add to dashboard Cite

Nearly isotropics-wave gap in the bulk of the optimally electron-doped superconductorNd1.85Ce0.15
Zhao
¹

2010
Phys. Rev. B
17
2
12
0
View full text Add to dashboard Cite

Evidence of a multiple boson emission in Sm _1−x Th _x OFeAs