Flux noise in high-temperature superconductors

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.Comment: 9 pages, 4 PostScript figures, to be published in Phys. Rev.

Loss of Superconducting Phase Coherence inYBa2Cu3O7Films: Vortex-Loop Un

“…Both results are fully consistent with the frequency and temperature variations observed in Ref. [13], which have also been associated with the dynamics of the v/a plasma above the KT transition [29].…”

Simulation of vortex noise in superconductors in weak applied magnetic fields

“…Flux noise in Josephson-junction arrays and high-temperature superconductors has been studied extensively, both experimentally and theoretically. [1][2][3][4][5][6][7][8][9][10][11][12][13] However, most theoretical calculations of the vortex noise spectrum has considered only the case of zero applied magnetic field. In this paper we study the effects of a weak applied magnetic field on the vortex noise power spectra in both twoand three-dimensional models for vortex fluctuations.…”

Fluctuation-dissipation theorem and flux noise in overdamped Josephson-junction arrays

“…Although in semi-phenomenological treatment [12][13][14]18] of twodimensional superconductors such decomposition seems to be inevitable, the case of an overdamped Josephson junction array allows for application of a more universal approach to calculation of the flux noise power spectrum. It is based on the direct relation (discussed in Sec.…”