NORMAL-STATE VERSUS PARACOHERENT RESISTIVITY IN GRANULAR COPPER-OXIDESUPERCONDUCTORS

In granular superconductors there are two distinct measurable electric al resistivities, namely the normal state resistivity and the paracohe rent resistivity. For the latter, we understand the resistivity due on ly to the intergrain boundaries, i.e, when the intragrains have become superconducting, and it is straightforwardly measurable from the curr ent-voltage characteristics below the critical temperature. We show th at the application cation of simple ideas on the framework of the effe ctive medium theory allows us to correlate the normal state and paraco herent resistivities with the degree of texturization of samples. In p articular, it is predicted that for non-textured samples the paracoher ent resistivity should equal one third the normal state residual resis tivity. Measurements on a batch of Y1Ba2Cu3O7-delta granular samples a re also presented to support, with no free parameters, our results. (C ) 1997 Published by Elsevier Science Ltd.