Vortex–antivortex behaviour and thermally activated phase slip in a polycrystallineYBa2Cu3O7−δ superconductor

Abstract

The temperature-dependent resistivity of a polycrystallineYBa2Cu3O7−δ superconductor under magnetic fields up to 5 kG has been investigated byemploying two models invoking different mechanisms of dissipation, namelythe Kosterlitz–Thouless (KT) model of vortex–antivortex unbinding fortwo-dimensional systems (2D) and the Ambegaokar–Halperin (AH) model of thermallyactivated phase slip (TAPS) for granular superconductors. The experimentalR–T data shows a partial agreement with the KT model in the intermediatetemperature range, justifying the picture of a quasi-two-dimensional polycrystallineYBa2Cu3O7−δ superconductor. Deviations from the KT model are apparent in the region near the onset transition temperature(TC) and the offsettransition temperature (TCO). On the other hand, excellent agreement is obtained with the AH model over the entire transitionrange. The resistivity curves under different magnetic fields show a scaling with the barrier parameter‘γ’ in the AH model. The resistivity curves can be made to merge with each other by plottingthe inverse square root of normalized resistance, i.e. versus γ∼A(H)(1−T/TC)m, where A(H) is an adjustable field-dependent parameter and‘m’ is a fixed parameter.