Vortex fluctuations in YBCO thin films: influence of weak magnetic fields

Peter Svedlindh; Orjan Festin; Klas Gunnarsson; Fredrik Ronnung; Dag Winkler

doi:10.1117/12.546515

25 May 2004 Vortex fluctuations in YBCO thin films: influence of weak magnetic fields

Peter Svedlindh, Orjan Festin, Klas Gunnarsson, Fredrik Ronnung, Dag Winkler

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 (S_φ(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 fS_φ = 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.

Citation Download Citation

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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