Correlation length and time in the vortex-glass critical regime in YBa 2Cu 3O 7−x films

Abstract

We report on the complex conductivity of a YBa 2Cu 3O 7−x microbridge in the presence of magnetic field 0.5 ≤B≤6.5 T applied parallel to the c-axis. A broad range of frequences 10 ≤ f ≤ 2 × 10 6 Hz for the transport current passing through the bridge allows us to explore the ac dynamical response of the vortices where conflicting results have been reported, in addition to the static characteristics of the vortex system ( dc limit). In consistency with the concept of a correlation length and a correlation time that diverge at the transition temperature T g(B), we demostrate that a single value for T g(B) can be identified in both the static and dynamical measurements, within an experimental uncertainty of 1 K. In conflict to previous reports, the real and imaginary components of the ac-linear voltage at T=T g (B) were found to follow the same power law V i ∝ V o ∝ f α, with α=0.82±0.05. Finally, as T→T g +, the critical scaling laws break down when the diverging vortex correlation length matches the film thickness of our sample and the correlation time exceeds 10 μs.