Zero bias anomalies in YBa2Cu3O7 tunnel junctions

Lesueur, J.; Greene, L. H.; Feldmann, W. L.; Inam, A.

doi:10.1016/0921-4534(92)90926-4

Cited by 171 publications

(110 citation statements)

References 29 publications

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“…Recently, a zero field splitting and a nonlinear evolution of the magnitude of the splitting with increasing applied magnetic field as predicted by Fogelström et al [59], has been reported for planar SIN-junctions [13,31] and for low temperature scanning tunneling spectroscopy experiments [64].…”

Section: Splitting Of the Zero Bias Conductance Peak By A Broken Timementioning

confidence: 99%

“…Initially, the Anderson-Appelbaum model [16,17] was used by most groups to give an interpretation of the observed zero bias conductance peak in tunneling spectroscopy experiments on HTS [12,30,31,33,34]. However, later on it became clear that the Appelbaum-Anderson model can explain only a few features of the experimental observations.…”

Section: Magnetic Impurity Scenariomentioning

confidence: 99%

“…Initially, it also was used to explain the experimentally observed zero bias conductance peak in tunnel junctions employing HTS electrodes [12,30,31,32,33,34]. However, as will be shown below the Appelbaum-Anderson model cannot account for the temperature and magnetic field dependence of the zero bias conductance peak observed for the HTS junctions including the GBJs.…”

Section: Appelbaum-anderson Modelmentioning

confidence: 99%

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Andreev bound states in high temperature superconductors

et al. 1998

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Abstract. Andreev bound states at the surface of superconductors are expected for any pair potential showing a sign change in different k-directions with their spectral weight depending on the relative orientation of the surface and the pair potential. We report on the observation of Andreev bound states in high temperature superconductors (HTS) employing tunneling spectroscopy on bicrystal grain boundary Josephson junctions (GBJs). The tunneling spectra were studied as a function of temperature and applied magnetic field. The tunneling spectra of GBJ formed by YBa2Cu3O 7−δ (YBCO), Bi2Sr2CaCu2O 8+δ (BSCCO), and La1.85Sr0.15CuO4 (LSCO) show a pronounced zero bias conductance peak that can be interpreted in terms of Andreev bound states at zero energy that are expected at the surface of HTS having a d-wave symmetry of the order parameter. In contrast, for the most likely s-wave HTS Nd1.85Ce0.15CuO4−y (NCCO) no zero bias conductance peak was observed. Applying a magnetic field results in a shift of spectral weight from zero to finite energy. This shift is found to depend nonlinearly on the applied magnetic field. Further consequences of the Andreev bound states are discussed and experimental evidence for anomalous Meissner currents is presented.

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Section: Splitting Of the Zero Bias Conductance Peak By A Broken Timementioning

confidence: 99%

Section: Magnetic Impurity Scenariomentioning

confidence: 99%

Section: Appelbaum-anderson Modelmentioning

confidence: 99%

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Andreev bound states in high temperature superconductors

et al. 1998

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“…Lesueur et al were the first to notice that a magnetic field can induce a split of the ZBCP in YBCO films, and proposed that it might be due to a Zeeman effect, under the assumption that the ZBCP itself is due to the presence of magnetic impurities in the vicinity of the barrier (Lesueur et al, 1992). Covington et al (Covington et al, 1997) further studied this effect, which was given a different interpretation by Fogelstrom et al (Fogelstrom et al, 1997) in terms of a Doppler shift of the energy of the ASJ surface states.…”

Section: High Z (110) Contacts Under Magnetic Fieldsmentioning

confidence: 99%

“…On (110) oriented films, a ZBCP and a Gap Like Feature (GLF) are both observed (Sharoni et al, 2002). Macroscopic contacts allowing in-plane tunneling into films having the (100) or (110) orientations have been produced by a number of techniques such as: using a Pb counter-electrode (sometimes with a thin Ag buffer layer in order to avoid massive oxygen out-diffusion, Lesueur et al 1992); or a copper counter electrode (Aprili et al, 1999). The method that we have been mostly using is sticking a small In dot on the film's fresh surface (Krupke and Deutscher, 1999).…”

Section: High Z (110) Contactsmentioning

confidence: 99%

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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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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Zero bias anomalies in YBa2Cu3O7 tunnel junctions

Cited by 171 publications

References 29 publications

Andreev bound states in high temperature superconductors

Andreev bound states in high temperature superconductors

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

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

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