Vortex avalanche phenomenon enhanced by thermomagnetic instabilities suppresses critical current in MgB2 films. This effect is investigated at 4.2 K by spectral noise power measurements up to 1 kHz with a dc superconducting quantum interference device apparatus. 1/f(gamma) behavior is shown at low frequencies in magnetic fields and feeding currents below j(c). gamma increases from 1 to 2 at increasing magnetic field, typical of fluxon avalanche processes. A peak in the power spectrum frequency behavior, observed only in magnetic field, is attributed to vortex-antivortex annihilations. Thermal instabilities disappear when an efficient thermal link to the He bath is attained and no vortex avalanche extra-noise is observed.
Vortex avalanche phenomena in MgB2 superconducting film studied by current noise measurements
EGGENHOFFNER, ROBERTO;CELASCO, EDVIGE;CELASCO, MARCELLO
2005-01-01
Abstract
Vortex avalanche phenomenon enhanced by thermomagnetic instabilities suppresses critical current in MgB2 films. This effect is investigated at 4.2 K by spectral noise power measurements up to 1 kHz with a dc superconducting quantum interference device apparatus. 1/f(gamma) behavior is shown at low frequencies in magnetic fields and feeding currents below j(c). gamma increases from 1 to 2 at increasing magnetic field, typical of fluxon avalanche processes. A peak in the power spectrum frequency behavior, observed only in magnetic field, is attributed to vortex-antivortex annihilations. Thermal instabilities disappear when an efficient thermal link to the He bath is attained and no vortex avalanche extra-noise is observed.
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