Dimensional crossover in flux dynamics in YBa 2Cu 3O 7− δ/PrBa 2(Cu 3− xGa x)O 7− δ superlattices

Abstract

Magnetic measurements were performed on a ring patterned [YBa 2Cu 3O 7− δ ] 56 Å/[PrBa 2(Cu 3− x Ga x )O 7− δ ] 125 Å superlattice with a transition temperature to superconductivity of T c=69 K. In this way, the critical current density j c( T), current–voltage characteristics E( j) and hysteresis M( H) were obtained. The normalized relaxation rate S( T) shows an anomalous drop for T≥65 K pointing to a reduced dissipation. An additional scaling analysis according to the vortex-glass theory reveals a crossover from 3D to quasi-2D behavior. A related anomaly was also observed in j c( T) behavior showing an unusual kink, from which a corresponding H– T borderline can be constructed, which is suggested to be due to a crossover from 3D to 2D collective pinning in accordance with the collective creep theory.