Scaling of cross-over currents in current-voltage characteristics of Y Ba2 Cu3 O7-δ films

We investigate current-voltage measurements of a superconductor in a magnetic field for a continuous superconducting transition. Existence of such a transition in the mixed state has been the subject of recent controversy due to flexibility in the conventional scaling analysis. To address this, we analyze current-voltage data using scaling forms based on the crossover current. One of these scaling forms, based on the logarithmic derivative of current-voltage isotherms, is a stringent test for a superconducting transition. Applying this derivative scaling test to the data shows marked disagreement with a superconducting transition, which indicates that one does not occur within the mixed state.