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

Systematic measurements of the in-plane fluctuation magnetoconductivity in a YBa2Cu3O7−δ 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 Tc, 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 Tc, evidence is found for a fluctuation regime beyond 3D XY. This new scaling can be interpreted as revealing an ultimate first-order character of the superconducting transition in YBa2Cu3O7−δ.