Vortex fluctuations in high-Tc films close to the resistive transition
2004 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 70, no 2, 024511Article in journal (Refereed) Published
Flux noise and ac susceptibility measurements have been performed on epitaxial YBa2Cu3O7 films to investigate dynamical properties of vortex fluctuations close to the resistive transition. The validity of the fluctuation-dissipation theorem is verified by the proportionality between flux noise and ac susceptibility results. The 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≈1.5–1.75. The characteristic frequency f0 exhibits a dramatic decrease close to the resistive transition; f0 decreases by 3–4 orders of magnitude in a temperature interval of ΔT≈1K. Moreover, the flux noise spectrum scales as fSϕ=g(f∕f0(T)), where g(∙) is a scaling function. The influence of a weak perturbing magnetic field (Hdc) on the characteristics of the flux noise spectrum has been investigated. While the general characteristics of the flux noise spectrum remain, except for a change in frequency dependence at f>f0, the characteristic frequency f0 exhibits a dramatic increase with increasing applied field; f0 increases by 3–4 orders of magnitude on increasing the field from zero to a few oersteds. Moreover, it is found that f0 is proportional to Hydc, with y≈1.15. The results are interpreted in terms of thermally generated vortex-antivortex fluctuations in combination with fluctuations of field-generated vortices.
Place, publisher, year, edition, pages
2004. Vol. 70, no 2, 024511
Engineering and Technology
IdentifiersURN: urn:nbn:se:uu:diva-91203DOI: 10.1103/PhysRevB.70.024511OAI: oai:DiVA.org:uu-91203DiVA: diva2:163856