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Proceedings Paper

Vortex fluctuations in YBCO thin films: influence of weak magnetic fields
Author(s): Peter Svedlindh; Orjan Festin; Klas Gunnarsson; Fredrik Ronnung; Dag Winkler
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Paper 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.

Paper Details

Date Published: 25 May 2004
PDF: 10 pages
Proc. SPIE 5469, Fluctuations and Noise in Materials, (25 May 2004); doi: 10.1117/12.546515
Show Author Affiliations
Peter Svedlindh, Uppsala Univ. (Sweden)
Orjan Festin, Uppsala Univ. (Sweden)
Klas Gunnarsson, Uppsala Univ. (Sweden)
Fredrik Ronnung, Chalmers Univ. of Technology (Sweden)
Dag Winkler, Chalmers Univ. of Technology (Sweden)

Published in SPIE Proceedings Vol. 5469:
Fluctuations and Noise in Materials
Dragana Popovic; Michael B. Weissman; Zoltan A. Racz, Editor(s)

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