Superconducting transport properties of epitaxial YBa2Cu3O7-δ thin films: A consistent description based on thermally-activated flux motion

The electrical-transport current properties of a series of epitaxial YBa2Cu3O7-δ thin films have been investigated using a range of techniques, including the activated electrical resistivity for fields B>Birr, the irreversibility field; the I-V curves for both B>Birr and B<Birr; and the resistive transitions in magnetic fields. The results are analyzed in the framework of a model for thermally-activated flux motion. The model utilizes a pinning barrier that is dependent on the current density J, temperature T, and applied magnetic field B, given by U0∝exp(-J/Jc0)(1-t)n/B, with n∼1.8. The exponential J dependence agrees well with the behavior U∝J-μ (μ∼0.8) of the collective-flux-creep model in the regime J<Jc0, while properly describing the finite pinning potential observed in the activated-flux-flow regime as J→0. The resulting analysis using this form for U0 provides a quantitatively self-consistent interpretation of all sets of measurements