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

TL;DR

This study measures flux noise spectrum and complex impedance in a high-temperature superconductor film, revealing vortex fluctuation behaviors and a crossover in vortex diffusion, advancing understanding of vortex dynamics in 2D superconductors.

Contribution

It provides experimental verification of theoretical predictions on vortex fluctuations and flux noise scaling in high-Tc films, highlighting a crossover in vortex diffusion regimes.

Findings

Flux noise spectra proportional to complex impedance

Logarithm of flux noise spectra has a common tangent with slope -1

Noise amplitude decreases as d^{-3} with height above the film

Abstract

The flux noise spectrum and complex impedance for a 500 {\AA} thick YBCO film are measured and compared with predictions for two dimensional vortex fluctuations. It is verified that the complex impedance and the flux noise spectra are proportional to each other, that the logarithm of the flux noise spectra for different temperatures has a common tangent with slope $\approx -1$, and that the amplitude of the noise decreases as $d^{-3}$, where $d$ is the height above the film at which the magnetic flux is measured. A crossover from normal to anomalous vortex diffusion is indicated by the measurements and is discussed in terms of a two-dimensional decoupling.