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  • 1
    Electronic Resource
    Electronic Resource
    Apparatus for vortex dynamics studies in high Tc samples using close cycle refrigerator and rf oscillators (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1494-1500 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design, fabrication, and performance of an apparatus for measurements of rf penetration depth in superconducting samples are described. The instrument makes use of a close-cycle helium refrigerator and is capable of measuring vortex dynamics in superconducting sample of volume as small as 1×10−3 cm3 with a signal-to-noise ratio of 1400. The system has been tested for a tunnel diode oscillator and an IC 74LS04 oscillator in the 3–5 MHz frequency range. Both magnetic field magnitude and angular variations to the resolution of 1 G and 0.05°, respectively, are possible with the apparatus. The system performance is evaluated by measuring the dynamical behavior of vortices in platelet samples of Bi2Sr2CaCu2O8 and (Bi-Pb)2Sr2Ca2Cu3O10 superconductors. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149612
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  • 2
    Electronic Resource
    Electronic Resource
    DC Electrical Resistivity Study of Granularity in YBa2CU3O7/Ag Composites (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 641-648 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Ag composites ; percolation ; granularity ; weak-link resistivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Temperature-dependent electrical resistivity in a set of YBa2Cu3O7−x /Ag composites, all prepared under an identical sintering schedule, is analyzed to extract granularity information. The weak-link resistivity ρ wl across the grain boundaries and the percolation factor α arising due to current frustration caused by misalignment of anisotropic grains and sample defects such as voids and cracks are estimated from the residual resistivity ρ0 and the temperature coefficient of resistivity dρ/dT. Variation of these parameters with Ag vol.% quantifying the extent of granularity indicates that granularity in the composites decreases and their electrical characteristics tend to be identical to that of Ag-free YBa2Cu3O7−x single crystals and epitaxial thin films as Ag vol.% approaches a value where onset of current percolation occurs through Ag channels. The increased α and decreased ρ wl observed at higher Ag vol.% explains the larger grains in the composites with narrow size distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022609432697
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  • 3
    Electronic Resource
    Electronic Resource
    Metastability-induced charge and spin fluctuations in 123 type superconductors (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 359-364 
    Details
    ISSN: 1572-9605
    Keywords: Vacancy ordering/disordering ; charge fluctuation ; spin fluctuation ; oxygen coordination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Various defects arising from lattice mismatch and coordination incompatibility at the cation sites are known to lend the cuprates a metastable state at temperatures and pressures where they exhibit superconductivity. The present paper considers the metastability induced by coordination incompatibility at Cu(1) sites in oxygen-deficient 123 type systems and looks for their possible effects on charge and spin degrees of freedom. Depending upon the concentration of oxygen vacancies, the resulting unstable charge state at the Cu(1) sites is shown to either temporally fluctuate or spatially equilibrate, providing a mechanism for the 90 K and the 60 K plateaus, with a peak in the former observed in the YBa2Cu3O7-y , samples prepared under thermodynamic equilibrium conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617972
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