Thermally activated phase-slip in high-temperature cuprates

Abstract

Gd1-x-zPrxCazBa2Cu3O7-δ (GdPrCa-123) high-temperature superconductor cuprate (HTSC) samples with 0.0⩽x⩽0.3 and 0.0⩽z⩽0.35 were prepared by standard solid-state reaction and characterized by XRD technique. The magnetoresistance of the samples were measured and analysed. The superconducting transition region broadened by the application of a magnetic field. The resistive transition showed two distinct parts. (1) A steep part near the onset of superconductivity, where the onset transition temperature remained unchanged. For the Gd0.85Ca0.15-123 sample, the steep part was more sensitive to the application of magnetic fields. (2) A transition tail part. The experimental data in this region were fitted with an Ambegakor and Halperin (AH) phase-slip model. The AH parameter, γ(H), was used to estimate the critical current density at zero temperature of samples at various magnetic fields. It was observed that the critical current density decreased with Pr substitution and increased with Ca substitution in Gd-123. An optimal value of the Ca doping concentration for increasing the critical current density was determined. We suggest that the Pr ion probably acts to enhance the weak link and the Ca ion acts as a flux pinning centre in the GdPrCa-123 system. Moreover, we observed that the AH parameter, γ, and activation energy, U0, depend not only on temperature and magnetic field, but also on the Pr and Ca ion concentrations.