High electric field study of the superconducting transition ofY Ba2Cu3O7−x

Abstract

The superconducting transitions ofY Ba2Cu3O7−x (YBCO) films of different thicknesses in high current densities and high electric fields areinvestigated. A pulsed-current technique allows for true four-probe measurements with a pulseduration as short as 50 ns, resulting in a significant reduction of self-heating. Electric fields up to900 V cm−1 can be applied without sample damage. The data are compared to a theoreticalmodel that describes the superconducting transition by the Hartree approximationof the Lawrence–Doniach model for a layered superconductor, together with atemperature correction in order to account for the self-heating. Although this modelfits the electric-field dependence of the resistivity of a 330 nm thick YBCO filmwell, it fails for a 36 nm ultra-thin film, where self-heating is much smaller. Thisobservation is a direct indication of intrinsic non-ohmic behaviour, resulting fromthe suppression of superconducting order parameter fluctuations in high electricfields.