Resistive states in thin films of Y2Ba4Cu8O16−δ

The resistance of a preferentially oriented thin film of Y2Ba4Cu8O16−δ has been measured as a function of temperature and fields up to 20 T oriented parallel to the c-axis. The normal state resistance could be well fitted by the Bloch-Grüneisen theory. Below Tc (≈ 80 K) the resistance transitions both in field and temperature could be separated in three regimes. A regime where the data can be analysed in terms of a model combining thermally activated flux flow and flux pinning due to dislocation lines. The upper critical field Bc2, obtained from this analysis, exhibits an upward curvature at low temperatures, possibly indicating a mixed s-d wave pairing. In the second regime just below Bc2 viscous forces are increasingly important for flux-line motion and the resistance is determined by the flux-flow resistance ϱf. At fields higher than Bc2 we find a large contribution of superconducting fluctuations to the conduction.