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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 957-959 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dense oriented superconducting Bi-Sr-Ca-Cu-O films having zero resistance as high as 100 K have been made using a technique in which spray deposited and pyrolyzed films are densified by either melt quenching or flux sintering. The highest Tc films were those prepared with PbO as a dopant/flux on MgO substrates. Films without lead doping prepared on both BeO and MgO substrates yielded resistive transitions of 81–83 K. For these latter films, it was demonstrated that a subsequent anneal in argon enhanced the Tc to 87 K. The films were characterized by x-ray diffraction, scanning electron microscopy, and four-point probe resistance measurements. The critical current density of a film having a Tc of 81 K was 4000 A/cm2 at 78 K and 14 000 A/cm2 at 55K.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 38 (1980), S. 497-534 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Using a generalized two-fluid picture to describe a quasi-one-dimensional superconductor near T c,we provide a heuristic derivation for a set of equations governing the temporal and spatial evolution of the charge imbalance (or branch imbalance) in the quasiparticles. We show that these equations are isomorphic to those that describe a simple electrical transmission line, so that charge imbalance waves may propagate in the superconductor in analogy with electrical signals that propagate down the transmission line. We propose as a model for a phase-slip center in a superconducting filament a localized Josephson oscillator coupled to the transmission line. Applying standard transmission-line theory to solve the problem, we show that the Josephson oscillations in the center generate charge imbalance waves that propagate out to a frequency-dependent distance of the order of the quasiparticle diffusion length λ Q *= (D Τ Q *)1/2 before they damp out. The time-averaged behavior of the model reduces to the earlier model of Skocpol, Beasley, and Tinkham. A novel consequence of the model is a prediction of intrinsic hysteresis in the dc current-voltage relation. The model also provides a convenient framework for dealing with ac effects in phase-slip centers, including resonance and synchronization in systems of closely spaced phase-slip centers and microbridges.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 38 (1980), S. 553-569 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: We report on experiments in which superconducting tin microstrips at temperatures 〉1/2T cwere illuminated, both cw and pulsed, by an argon laser. The illuminated films cannot in general be modeled in terms of a spatially uniform effective temperature. Even when care is taken to ensure that the illumination is spatially uniform to within ~5% over the area of the strips, the resistive transition far from T cextends over a range of laser powers which is ~25% of the power necessary to drive the strips completely normal. The critical current of each strip decreases smoothly to zero and the current-voltage characteristics smoothly approach that of the normal state as the laser power is increased, indicating the probable absence of a first-order transition in any section of the strips. However, the behavior of the current-voltage characteristics of one strip is consistent with what might be expected if a spatially inhomogeneous state were to develop suddenly as the laser power is increased. Possible explanations are discussed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 28 (1977), S. 519-533 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show that there is a large class of quasiparticle distributions, qualitatively similar to those predicted for optically excited superconductors, that may lead to a spatial instability driven by quasiparticle diffusion. The resultant inhomogeneous state would consist of distinct regions characterized by a length scale λ (quasiparticle diffusion length) and different energy gaps. We discuss the dynamics of this inhomogeneous state, and its experimental implications.
    Type of Medium: Electronic Resource
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