Critical Current Enhancement due to an Electric Field in a Granular d-Wave Superconductor

We study the effects of an electric-field in the transport properties of bulk granular superconductors with different kinds of disorder. We find that for a d-wave granular superconductor with random $\pi$-junctions the critical current always increases after applying a strong electric field, regardless of the polarity of the field. This result plus a change in the voltage as a function of the electric field are in good agreement with experimental results in ceramic high T_c superconductors.