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

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