Gap anisotropy and Fermi velocity in oriented YBa2Cu3O7−δ from point contact spectroscopy

Hass, N.; Ilzycer, D.; Deutscher, G.; Desgardin, G.; Monot, I.; Weger, M.

doi:10.1016/0921-4534(93)90877-s

Cited by 13 publications

(29 citation statements)

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“…Point-contact spectroscopy (PCS) data of Srikanth & Raychaudhuri [30] also indicate a structure at 5 rneV for an YBCO-Au contact. Indications of such a structure were also seen by Hass et al [31]. A strong ZBA in the organic superconductor ET was also reported [26] and its magnetic field dependence studied [32].…”

Section: Experimental Manifestations Of the Zbasupporting

confidence: 65%

Solution of the Eliashberg equations for a very strong electron‐phonon coupling with a low‐energy cutoff

et al. 1995

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We solve the Eliashberg equations for the case of an explicit dependence of the interactions, and of the resulting self-energies XI (I?, a), X2(% w ) . We consider a strong energy-dependence of the electron-electron scattering-rate r;', which is associated with a strong energy-dependence of the electron-phonon matrix element g(k,k'). We characterize this energy-dependence by a cutoff tl, which is of the order of the phonon frequency Up),. We find that we can account for a large number of unexpected features of the superconductivity of the cuprates by the BCS electron-phonon theory, if we consider very large values of the McMillan coupling constant Aph, and small values of the cutoff C1. Specifically, the Coulomb interaction is found not to depress T,; thejsotope effect is strongly reduced when c1

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Section: Experimental Manifestations Of the Zbasupporting

confidence: 65%

Solution of the Eliashberg equations for a very strong electron‐phonon coupling with a low‐energy cutoff

et al. 1995

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“…This apparent contradiction between experiment and theory was explained by Deutscher and Nozieres (Deutscher and Nozieres, 1994) as resulting from a renormalization of the Fermi velocity in the Point Contact experiments, which is different from the full quasi-particle renormalization. This special renormalization also explains the occurrence of strong ASJ reflections in heavy Fermions (Hasselbach et al, 1993).…”

Section: Introductionmentioning

confidence: 61%

“…In fact, observation of ASJ reflections turned out to be relatively easy. I believe that (Hass et al, 1992) were the first to report such observations on single crystal quality YBCO samples, using a Gold tip as the normal metal. For reasons that became clear only later, and that had to do with the d-wave symmetry of the order parameter in this superconductor, the fit to BTK theory was not perfect, but a gap value of 18-20 meV could clearly be obtained.…”

Section: Introductionmentioning

confidence: 99%

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Andreev–Saint-James reflections: A probe of cuprate superconductors

2005

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Electrical transport through a normal metal / superconductor contact at biases smaller than the energy gap can occur via the reflection of an electron as a hole of opposite wave vector. The same mechanism of electron-hole reflection gives rise to low energy states at the surface of unconventional superconductors having nodes in their order parameter. The occurrence of electron-hole reflections at normal metal / superconductor interfaces was predicted independently by Saint James and de Gennes and by Andreev, and their spectroscopic features discussed in detail by Saint James in the early sixties. They are generally called Andreev reflections but, for that reason, we call them Andreev -Saint James (ASJ) reflections. We present a historical review of ASJ reflections and spectroscopy in conventional superconductors, and review their application to the High Tc cuprates. The occurrence of ASJ reflections in all studied cuprates is well documented for a broad range of doping levels, implying that there is no large asymmetry between electrons and holes near the Fermi level in the superconducting state. In the underdoped regime, where the pseudo-gap phenomenon has been observed by other methods such as NMR, ARPES and Giaever tunneling, gap values obtained from ASJ spectroscopy are smaller than pseudo-gap values, indicating a lack of coherence in the pseudo-gap energy range. Low energy surface bound states have been observed in all studied hole doped cuprates, in agreement with a dominant d-wave symmetry order parameter. Results are mixed for electron doped cuprates. In overdoped Y Ba 2 Cu 3 O 7−δ (δ < 0.08) and La 2−x SrxCuO 4 , ASJ spectroscopy is consistent with the presence of an additional imaginary component of the order parameter. Results of ASJ spectroscopy under applied magnetic fields are also reviewed. A short section at the end is devoted to some recent results on spin effects. * Electronic address: guyde@tau.ac.il 2

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“…where, is Plancks constant, is the Fermi velocity and is the energy band gap of the YBCO thin film. Using this equation and values from [17], we calculate a coherence length ( ) of about 7 nm at 4.2 K for our case.…”

Section: Introductionmentioning

confidence: 99%

Micron-Sized Constrictions Fabricated Using the Femtosecond Laser Technique on YBCO Thin Films

Umenne

2019

J Supercond Nov Magn

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In this paper, I report on the fabrication of micron-sized constrictions in YBCO thin films using the femtosecond laser technique.The constrictions are S-shaped superconducting weak links fabricated on YBCO thin films. The constrictions show a measurable superconducting current flowing through them. Current -Voltage (I-V) characteristics were used to determine the critical current of the constrictions at 77 K. The width of the constrictions was determined at the narrowest point using SEM (Scanning electron microscope). Three micron-sized constrictions were fabricated with a width of 2.88 µm, 1.72 µm, 1.69 µm and a length of 5 µm.Based on the width and length of these constrictions in relation to the coherence length ( ) of the YBCO these constrictions should conduct supercurrent by Abrikosov vortices. The SEM images show that the femtosecond laser heats the samples beyond the geometric boundary, damaging some of the superconductive phase of the YBCO constrictions. As a result, the constrictions conduct current by one-dimensional depairing.

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Gap anisotropy and Fermi velocity in oriented YBa2Cu3O7−δ from point contact spectroscopy

Cited by 13 publications

References 15 publications

Solution of the Eliashberg equations for a very strong electron‐phonon coupling with a low‐energy cutoff

Solution of the Eliashberg equations for a very strong electron‐phonon coupling with a low‐energy cutoff

Andreev–Saint-James reflections: A probe of cuprate superconductors

Micron-Sized Constrictions Fabricated Using the Femtosecond Laser Technique on YBCO Thin Films

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