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  • Artikel  (16)
  • YBCO  (16)
  • 1995-1999  (16)
  • Elektrotechnik, Elektronik, Nachrichtentechnik  (16)
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  • Artikel  (16)
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  • 1
    Digitale Medien
    Digitale Medien
    Investigation of the Symmetry of the Pairing State in YBa2Cu3O7−δ Using the Nonlinear Transverse Magnetic Moment: Experimental Results (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 99-103 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Nonlinear Meissner effect ; pairing state ; YBCO
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract Measurements of the nonlinear transverse magnetic moment have been carried out on disk-shaped samples of YBCO, using an ac technique. Numerical calculations for a d x 2 - y 2 pairing state predict a fourfold modulation of this moment as a function of the angle between the applied magnetic and the crystalline axes for a magnetic field applied in the a–b plane of the sample. Our results imply a minimum nonzero gap at all points on the Fermi surface.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007738123479
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  • 2
    Digitale Medien
    Digitale Medien
    Unusual Photon Energy Dependence of the Cooper Pair Breaking Rate in YBa2Cu3O7−δ Epitaxial Thin Films (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 675-680 
    Details
    ISSN: 1572-9605
    Schlagwort(e): YBCO ; Cooper pair ; thin films ; ultrafast phenomena
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The transient photoimpedance response of epitaxial YBa2Cu3O7−δ thin films has been studied using 100 fs Ti:Sapphire laser pulse excitation. Both temperature and photon energy dependence of the fast optical response signal (whose temperature dependence can be explained by a kinetic inductance model involving Cooper pair breaking) were studied. The pair breaking rate is strongly photon energy-dependent, with a resonance around 1.5 eV with a width of only 100 meV, which is very surprising given the strong electron correlation in this metallic system and may be explained in terms of the stripe phase model.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007708304186
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  • 3
    Digitale Medien
    Digitale Medien
    Investigation of Oxidation Kinetics of YBa2Cu3O7−x Ceramics by the Acoustic Emission Method (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 275-276 
    Details
    ISSN: 1572-9605
    Schlagwort(e): YBCO ; acoustic emission ; absorption
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The oxidation kinetics of YBa2Cu3O7−x ceramics has been investigated by the acoustic emission method. It is observed that the oxidation follows an exponential law. For YBCO the exponential index τ is a specific parameter and is equal to 1.7 s±10%. It is confirmed that the related narrow surface layer is first oxidized, and oxygen dissolution in the material is controlled by the speed of volume diffusion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022688018815
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  • 4
    Digitale Medien
    Digitale Medien
    Experimental determination of the symmetry of the order parameter in YBCO (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 491-494 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Superconductivity ; pairing symmetry ; YBCO ; SQUID
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract At present, the symmetry of the order parameter in the high temperature superconductor YBCO is quite controversial. Recent experiments using SQUIDs and Josephson junctions appear to support competing theories, with some experiments supporting a dx2−y2 pairing symmetry for the order parameter and others a s-wave pairing symmetry. We note that a number of factors such as trapped flux, magnetic field gradients and SQUID asymmetries could lead such measurements astray. We use a Scanning SQUID Microscope and a time-reversal invariance test to resolve these experimental problems. We find the order parameter in YBCO has a time-reversal invariant dx2−y2 symmetric component. We estimate the amplitude of anyimaginary s-wave symmetric component to be less than 4% and anyreal s-wave component to be less than 82%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00722838
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  • 5
    Digitale Medien
    Digitale Medien
    Upper critical and irreversibility fields in selectively doped YBa2Cu3O7 (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 619-620 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Irreversibility ; critical ; field ; doped ; YBCO
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The electrical resistivity of (Y1−xPrx)Ba2Cu3O7−gd and YBa2(Cu1−xZnx)3O7−δ thin films and (Y1−x. Tbx)Ba2Cu3O7−δ thin films and single crystals has been measured as a function of 0≤x≤xcrit, 2K≤T≤300K and OTH≤20T. The samples were oriented withc-axis parallel to applied fields. Upper critical field Hc2 and irreversibility field Hirr values have been determined from these measurements. Increased Tb doping appears to shift Hirr to higher temperatures. This coupled with observed twin peaks in magnetization measurements reflects an enhancement of flux pinning. Unlike Tb which does not appear to alterT c , Pr and Zn doping of this system tends to depress bothT c and the slope of the mean field normal phase-mixed phase boundary line (dH c2/dT).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00727445
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  • 6
    Digitale Medien
    Digitale Medien
    Studies on microbridges of superconducting YBCO thin film (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 211-216 
    Details
    ISSN: 1572-9605
    Schlagwort(e): YBCO ; microbridges ; microwave effects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract Critical current densities of the superconducting Y-Ba-Cu-O (YBCO) films have been observed to decrease with the increase of power of microwave radiation. Presence of Josephson type of junctions in the microbridges has been established from the microwave irradiation and magnetic field studies. BCS energy gap parameter (2Δ/kT c ) has been calculated from thedI/dV characteristics and found to be 3.7 at 13 K.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00728305
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  • 7
    Digitale Medien
    Digitale Medien
    A new type of biepitaxialc-axis tilted YBCO Josephson junction (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 237-244 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Josephson junctions ; YBCO ; grain boundary ; MgO seed layer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract A novel fabrication procedure of high critical temperature superconductor Josephson junctions (HTCSJJ) has been developed by a 90° rotation of YBa2Cu3O7−x c-axis around an in-plane direction, on the basis of concepts of the biepitaxial technique. YBa2Cu3O7−x grows oriented along (001) direction on a MgO seed layer deposited on a (110) SrTiO3 substrate and along (110) direction on the bare substrate. Josephson junctions of good quality were obtained exhibiting RSJ behavior and features characteristic of HTCSJJ phenomenology. Even if not uniform, in some samples, the nature of the critical currentI c is completely Josephson, as resulting from theI c dependence on the applied magnetic field. The maximum measuredI c R N value atT=4.2K is 2mV.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00728309
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  • 8
    Digitale Medien
    Digitale Medien
    Photo-Thermal Transport Effects in a Thick Film YBCO Bolometer Under Magnetic Fields (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 463-469 
    Details
    ISSN: 1572-9605
    Schlagwort(e): YBCO ; thick film ; vortices ; pinning ; bolometer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract Thick (~50 μm) YBCO superconducting film bolometers have been fabricated to operate in the temperature range 89–92 K. Responsivities greater than 1 V/W have been achieved by biasing with a current slightly less than that of the critical current, and observing the photo-voltage in the resistive state. The time response of these films due to photo-conduction is slow (ms). The present work concentrates on the resistive transition and the width of the photo-signal peak under the effect of applied magnetic fields. The width of the photo-signal peak over the transition is found to be strongly magnetic field dependent at low field values while at higher field values it has been used to determine a value for the vortex tilt modulus. Further, it is found that a temperature difference in the position of the photo-signal peak relative to that of the dR/dT peak changes with applied field.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022657900890
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  • 9
    Digitale Medien
    Digitale Medien
    A Model for the Crystal Growth of YBa2Cu3O y (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 347-352 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Crystal growth ; morphology ; YBCO ; terraced crystals ; step growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The crystal growth and crystal morphology are very important properties of YBa2Cu3O y superconductors. In this work, we approach these problems with polycrystals. Several typical crystal morphologies were observed by scanning electron microscopy, and the terraced crystals with a layer-by-layer structure were found to be the major form for the well-grown YBa2Cu3O y . To interpret the results, a step-growth model was proposed. In this model, each crystal terrace is close-packed with crystal particles in order. And the particles, each consisting of tens of crystal cells, are movable during crystal growth. Particles at edges or margins of small crystals can move to their larger neighboring crystals through diffusion. With this particle diffusion, small crystals vanish and large crystals grow larger. This proposed model is confirmed by experimental observations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022646713766
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  • 10
    Digitale Medien
    Digitale Medien
    Specific Heat of YBa2Cu3O7−−δ and (La2−xSrx)CuO4: Evidence for d-Wave Pairing (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 105-111 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Specific heat ; YBCO ; LSCO ; d-wave
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract New low-temperature specific-heat data for YBa2Cu3O7−δ, 0≤δ≤0.2, and (La1.85Sr0.15)CuO4 in magnetic fields (H) to 9 T are reported. They show features predicted for the lines of nodes in the energy gap that are expected for d-wave pairing; for H=0, a T 2 term; for H≠0 an H 1/2 T term with a crossover to a more complicated T dependence at higher T and lower H. The results are compared with recent measurements in other laboratories.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007790107549
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  • 11
    Digitale Medien
    Digitale Medien
    High-Q oscillator measurements of vortex properties in YBa2Cu3O7−δ (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 667-668 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Mechanical oscillator ; YBCO ; vortex pinning ; twin boundary
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract High-Q oscillators, vibrating with extremely small tilt angles, ∼10−7 radians, were used to study vortex behavior in single crystal YBa2Cu3O7−δ. Systematic changes in the dissipation and frequency of the oscillator were explored for various fields both parallel and perpendicular to twin boundaries. At the small tilt oscillation amplitudes employed here, a number of features were observed which are not evident at the more typically utilized large oscillation amplitudes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00727469
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  • 12
    Digitale Medien
    Digitale Medien
    Use of tricrystal junctions to probe the pairing state symmetry of YBa2Cu3O7 (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 679-680 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Pairing ; symmetry ; YBCO ; tricrystal ; junction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract We have developed a new method of probing superconducting pairing state symmetry, by using tricrystal devices analogous tos-d corner junctions. Two central peaks are observed in the field-modulated critical currents of frustrated YBCO tricrystal junctions operating in the short junction limit, consistent with predominantly $$d_{x^2 - y^2 } $$ — wave pairing symmetry with little or no imaginarys-wave component. However, our results are consistent with a real combination of larged-wave and smalls-wave components. A single peak is also observed for frustrated tricrystal junctions operating in the long junction limit, and it is shown theoretically that the behaviors ofs- andd-wave superconductors are indistinguishable in this limit.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00727475
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  • 13
    Digitale Medien
    Digitale Medien
    RF measurements on a TE011 YBCO cavity at 8 GHz (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 753-757 
    Details
    ISSN: 1572-9605
    Schlagwort(e): YBCO ; surface resistance ; penetration depth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract In the present work a cavity fully coated with an YBCO thick film was fabricated using an improved electrophoretic deposition technology with a special attempt to avoid the possible contamination of the superconducting powder during the milling process in the suspension preparation. A microwave experimental set-up was constructed to measure the rf behavior of the cavity in a wide temperature range. The loaded quality factorQ 1 and the shift of the resonant frequency vs. the temperature at various rf magnetic fields have been measured. Furthermore, the surface resistance and the penetration depth determined from the measurements were compared with the numerical calculation in the framework of BCS theory, showing good agreement with the theoretical predictions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00727499
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  • 14
    Digitale Medien
    Digitale Medien
    Large ultrasonic attenuation at Tc in YBa2Cu3O7−x (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 647-648 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Ultrasonic ; YBCO ; polaronic condensation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract We investigated elastic anomalies of sintered YBa2Cu3O7−x (x=0.35) superconductor around the critical temperature (Tc=60 K). We observed the non-symmetric and large attenuation peak (2 dB/cm at 9.7 MHz) at Tc, which was due to the lattice softening caused by the strong correlation between carriers and local lattice distortion. The rapid decrease of ultrasonic attenuation just below Tc suggested a condensation mechanism. These supported the polaronic condensation in high-Tc superconductivity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00727459
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  • 15
    Digitale Medien
    Digitale Medien
    New aspects in the microstructure of YBCO melt-textured high-T c superconductors (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 535-538 
    Details
    ISSN: 1572-9605
    Schlagwort(e): YBCO ; microstructure ; phase ; microanalysis ; pinning ; melt-textured samples
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The microstructure and phase constitution of bulk textured YBCO samples prepared by the modified MTG method in the longitudinal temperature gradient have been investigated. We found the existence of an unusual phase between stacked platelets. Microanalysis shows that this phase may be characterized as Y-143. This phase forms ellipsoid-like particles with a typical size about 0.05–2μ which can play the role of effective pinning centers. The reason for the phase formation is discussed. We assume that this phase exists commonly in melt-textured samples prepared in the temperature field gradient.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00723527
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  • 16
    Digitale Medien
    Digitale Medien
    Influence of substrate on the excess electrical noise in the normal state of YBa2Cu3O7-δ thin films (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 307-310 
    Details
    ISSN: 1572-9605
    Schlagwort(e): YBCO ; electrical noise ; substiates ; normal state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract We present our studies of the low-frequency excess electrical noise in YBa2Cu3O7-δ thin films in the normal state. We have studied films with varying microstructure deposited on different substrates. The frequency dependence and bias current dependence of the noise power spectral density agree with the behavior expected for noise due to conductance fluctuations. Comparison between films on different substrates shows that the presence of defects such as grain boundaries in the film correlate with significantly enhanced noise levels. The noise levels in our good-quality epitaxial films are several orders of magnitude lower than the anomalously large noise magnitudes reported for YBa2Cu3O7-δ in most of the earlier studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00727553
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