Fluctuation-induced resistivity in YBCO across T-c from angular measurements in magnetic field.

We present various sets of resistive transitions in an YBCO thin film, as a function of the temperature, magnetic field and field orientation theta with respect to the (a,b) planes. We show that the resistivity undergoes an angular scaling only above a characteristic field-dependent temperature T-f(H), where T-f is below the mean-field transition temperature T-C(H). The scaling function found is that expected for a strongly coupled layered superconductor. It is shown that the interacting fluctuations theory describes with details the data for T>T-f(H), with a very reduced set of parameters. Comparison with data taken on untwinned samples reveals that the upper part of the transition is identical for films and single crystals, and that the same theory works well in both cases. In addition, Bardeen-Stephen flux flow is observed in the crystal only, and in a small region of H and T. We conclude that in a wide portion of the H-T plane the dissipation is due to intrinsic properties only (order parameter fluctuations), while only at lower temperatures the pinning becomes relevant, as supported by the breakdown of the angular scaling and by the fact that pure crystals and films appear to be different at low temperatures only.