5 July 1996 Thermodynamical fluctuations and critical behavior in weakly disordered YBCO thin and ultrathin films
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The specific role of disorder in the transport properties of YBCO has been investigated, using both light-ion irradiation of thin films to finely tune the amount of atomic disorder, and ultra-thin films grown to study possible dimensional effects. For weak disorder, the samples display a resistive transition typical of the mean-field paraconductive regime of an homogeneous media, well described by the Lawrence and Doniach model for layered superconductors. As the disorder increases, two effects take place. First, the c-axis coherence length becomes shorter, leading to a more anisotropic material, as shown by the excess conductivity above Tc. Second, an incipient granularity is revealed, leading to a less sharper transition, which is analyzed within the random 3D XY critical model for the paracoherence transition. Two main results are derived: and experimental test of the Ginzburg criteria for the paracoherence transition, and a new fluctuation regime in a nanometric grain size superconductors.
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Jerome Lesueur, Jerome Lesueur, S. Degoy, S. Degoy, Marco Aprili, Marco Aprili, D. Chambonnet, D. Chambonnet, D. Keller, D. Keller, } "Thermodynamical fluctuations and critical behavior in weakly disordered YBCO thin and ultrathin films", Proc. SPIE 2697, Oxide Superconductor Physics and Nano-Engineering II, (5 July 1996); doi: 10.1117/12.250233; https://doi.org/10.1117/12.250233

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