Flux noise in high-temperature superconductors

TL;DR

This paper calculates the flux noise spectrum in high-temperature superconductor Bi-2212, revealing a transition from white noise to 1/omega^(3/2) behavior influenced by temperature, using a theoretical model based on vortex dynamics.

Contribution

It introduces a detailed theoretical model incorporating vortex diffusion and interactions to predict flux noise spectra in high-temperature superconductors.

Findings

White noise at low frequencies

1/omega^(3/2) spectrum at high frequencies

Cross-over frequency varies with temperature

Abstract

Spontaneously created vortex-antivortex pairs are the predominant source of flux noise in high-temperature superconductors. In principle, flux noise measurements allow to check theoretical predictions for both the distribution of vortex-pair sizes and for the vortex diffusivity. In this paper the flux-noise power spectrum is calculated for the highly anisotropic high-temperature superconductor Bi-2212, both for bulk crystals and for ultra-thin films. The spectrum is basically given by the Fourier transform of the temporal magnetic-field correlation function. We start from a Berezinskii-Kosterlitz-Thouless type theory and incorporate vortex diffusion, intra-pair vortex interaction, and annihilation of pairs by means of a Fokker-Planck equation to determine the noise spectrum below and above the superconducting transition temperature. We find white noise at low frequencies omega and a spectrum proportional to 1/omega^(3/2) at high frequencies. The cross-over frequency between these regimes strongly depends on temperature. The results are compared with earlier results of computer simulations.