Vortex-antivortex behaviour and thermally activated phase slip in a polycrystalline YBa2Cu3O7-δ superconductor

The temperature-dependent resistivity of a polycrystalline YBa2Cu3O7-δ superconductor under magnetic fields up to 5 kG has been investigated by employing two models invoking different mechanisms of dissipation, namely the Kosterlitz-Thouless (KT) model of vortex-antivortex unbinding for two-dimensional systems (2D) and the Ambegaokar-Halperin (AH) model of thermally activated phase slip (TAPS) for granular superconductors. The experimental R-T data shows a partial agreement with the KT model in the intermediate temperature range, justifying the picture of a quasi-two-dimensional polycrystalline YBa2Cu3O7-δ superconductor. Deviations from the KT model are apparent in the region near the onset transition temperature (TC) and the offset transition temperature (TCO). On the other hand, excellent agreement is obtained with the AH model over the entire transition range. 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 plotting the inverse square root of normalized resistance, i.e. √(RN)/R versus γ∼A(H)(1-T/TC)m, where A(H) is an adjustable field-dependent parameter and 'm' is a fixed parameter