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25 May 2004 Vortex fluctuations in YBCO thin films: influence of weak magnetic fields
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Proceedings Volume 5469, Fluctuations and Noise in Materials; (2004) https://doi.org/10.1117/12.546515
Event: Second International Symposium on Fluctuations and Noise, 2004, Maspalomas, Gran Canaria Island, Spain
Abstract
Flux-noise and ac susceptibility measurements have been performed on epitaxial YBa2Cu3O7 films. The validity of the fluctuation-dissipation-theorem is verified by the proportionality between flux noise and ac susceptibility results. The nominal zero-field flux-noise spectrum (Sφ(f)) can be characterized as follows: Below a temperature dependent frequency f0(T), the flux-noise spectrum is frequency independent. For frequencies f > f0(T), the flux-noise spectrum follows f-x, with x ≈ 1.7-1.8. f0 decreases by 4 orders of magnitude in a temperature interval of ▵T ≈ 0.5 K. Moreover, the flux-noise spectrum scales as fSφ = g(f/f0(T)), where g(·) is a scaling function. The influence of weak perturbing magnetic fields was investigated. While the general characteristics of the flux-noise spectrum remain, the characteristic frequency f0 increases by 3-4 orders of magnitude increasing the field from zero to 1 Oe. Flux-noise measurements performed using a compensating field to reduce the residual field in the experimental setup reveal new features of the measured noise spectra. The flux-noise is dominated by thermally generated vortex-antivortex pair fluctuations at temperatures below the mean-field transition temperature, while with decreasing temperature there is a transition to vortex fluctuations being dominated by field generated vortices.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Peter Svedlindh, Orjan Festin, Klas Gunnarsson, Fredrik Ronnung, and Dag Winkler "Vortex fluctuations in YBCO thin films: influence of weak magnetic fields", Proc. SPIE 5469, Fluctuations and Noise in Materials, (25 May 2004); https://doi.org/10.1117/12.546515
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