Dynamic of vortices in YBa2Cu3O7-δ single crystal near the temperature of the vortex glass transition by the use of voltage noise measurements

We have studied the voltage noise Vn and the voltage noise spectral density SV of YBa2Cu3O7-δ superconductor in the regime of high magnetic field. Our studies were performed in a large range of temperature T (70 K-90 K) covering the vortex-glass-vortex-liquid transition which appears at Tg temperature. The sample is driving by a current I=1 nA, under a different high magnetic fields H (2.4 T, and 5 T). The noise spectral density noted SV(f) exhibits a 1/fα. Approaching Tg the vortex glass transition, the voltage noise spectral density SV(T) is found to vanish critically according to the critical power law SV ∝(T-Tg)x, with x=1.64±0.1 which represents the critical exponent. The behaviour exhibited by Sv(T) cannot be simply interpreted by thermal fluctuations as we conclude by comparing SV(T) with (dR/dT)2 curve. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)