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⩽0.3and 0.0⩽z⩽0.35 were prepared by standard solid-state reaction andcharacterized by XRD technique. The magnetoresistance of the samples weremeasured and analysed. The superconducting transition region broadened by theapplication of a magnetic field. The resistive transition showed two distinctparts. (1) A steep part near the onset of superconductivity, where the onsettransition temperature remained unchanged. For the Gd0.85Ca0.15-123sample, the steep part was more sensitive to the application of magneticfields. (2) A transition tail part. The experimental data in this region werefitted with an Ambegakor and Halperin (AH) phase-slip model. The AHparameter, γ(H), was used to estimate the critical current density atzero temperature of samples at various magnetic fields. It was observed thatthe critical current density decreased with Pr substitution and increased withCa substitution in Gd-123. An optimal value of the Ca doping concentration forincreasing the critical current density was determined. We suggest that the Prion probably acts to enhance the weak link and the Ca ion acts as a flux pinningcentre in the GdPrCa-123 system. Moreover, we observed that the AH parameter,γ, and activation energy, U0, depend not only on temperature andmagnetic field, but also on the Pr and Ca ion concentrations.Part of this paper has been reported at the MSM-99 conference [26].