Transport properties of ultrathin YBa2Cu3O7−δ layers: Evidence for two-dimensional vortex fluctuations

Abstract

We report on the transport properties of ultrathin ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (YBCO) layers, and compare the results with predictions of the Ginzburg-Landau Coulomb-gas (GLCG) model for two-dimensional (2D) vortex fluctuations. We find that the normalized flux-flow resistances for several ultrathin YBCO structures collapse onto a single universal curve, as predicted by the model. In addition, the values for the Kosterlitz-Thouless transition temperature ${\mathit{T}}_{\mathrm{KT}}$ and the Ginzburg-Landau temperature, ${\mathit{T}}_{\mathit{c}0}$, obtained by separate analyses of I-V and resistance data within the context of the GLCG model, are in general agreement. Finally, we find that the properties of a series of YBCO/${\mathrm{Pr}}_{0.5}$ ${\mathrm{Ca}}_{0.5}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ superlattice structures are consistent with the GLCG treatment for anisotropic, 3D layered superconductors.