Vortex Fluctuations in High-Tc Films : Flux Noise Spectrum and Complex Impedance

• The flux noise spectrum and complex impedance for a 500 Å thick YBCO film are measured and comparedwith predictions for two-dimensional vortex fluctuations. It is verified that the complex impedanceand the flux noise spectra are proportional to each other, that the logarithm of the flux noise spectrafor different temperatures has a common tangent with slope 21, and that the amplitude of the noisedecreases as d23, where d is the height above the film at which the magnetic flux is measured. Acrossover from normal to anomalous vortex diffusion is indicated by the measurements and is discussedin terms of a two-dimensional decoupling.

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