The electrical-transport current properties of a series of epitaxial ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ thin films have been investigated using a range of techniques, including the activated electrical resistivity for fields B>${\mathit{B}}_{\mathrm{irr}}$, the irreversibility field; the I-V curves for both B>${\mathit{B}}_{\mathrm{irr}}$ and B<${\mathit{B}}_{\mathrm{irr}}$; 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 ${\mathit{U}}_0$∝exp(-J/${\mathit{J}}_{\mathit{c}0}$)(1-t${)}^{\mathit{n}}$/B, with n∼1.8. The exponential J dependence agrees well with the behavior U∝${\mathit{J}}^{\mathrm{-}\mathrm{\mu }}$ (μ∼0.8) of the collective-flux-creep model in the regime J<${\mathit{J}}_{\mathit{c}0}$, while properly describing the finite pinning potential observed in the activated-flux-flow regime as J→0. The resulting analysis using this form for ${\mathit{U}}_0$ provides a quantitatively self-consistent interpretation of all sets of measurements.

Close

PrevNext

View figure in article