Scaling beyond 3D XY in the fluctuation conductivity of YBa2Cu3O7-δ

Systematic measurements of the in-plane fluctuation magnetoconductivity in a YBa2Cu3O7-delta single crystal are presented. Fields up to 500 mT were applied either parallel or perpendicular to the Cu-O planes. The data reveal the occurrence of Gaussian-fluctuation regimes far from the transition. Closer to T-c, the results clearly show the occurrence of a genuine critical regime, where the exponent is consistent with predictions for the 3D XY universality class with model-E dynamics. Still closer to T-c, evidence is found for a fluctuation regime beyond 3D XP. This new scaling can be interpreted as revealing an ultimate first-order character of the superconducting transition in YBa2Cu3O7-delta. (C) 1999 Elsevier Science Ltd. All rights reserved.