TRANSPORT-PROPERTIES OF ULTRATHIN YBA2CU3O7-DELTA LAYERS - EVIDENCE FOR 2-DIMENSIONAL VORTEX FLUCTUATIONS

We report on the transport properties of ultrathin YBa2Cu3O7-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 T(KT) and the Ginzburg-Landau temperature, T(c0), 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/Pr0.5Ca0.5Ba2Cu3O7-delta superlattice structures are consistent with the GLCG treatment for anisotropic, 3D layered superconductors.