Normal state versus paracoherent resistivity in granular copper-oxide superconductors

Abstract

In granular superconductors there are two distinct measurable electrical resistivities, namely the normal state resistivity and the paracoherent resistivity. For the latter, we understand the resistivity due only to the intergrain boundaries i.e. when the intragrains have become superconducting, and it is straightforwardly measurable from the current-voltage characteristics below the critical temperature. We show that the application of simple ideas on the framework of the effective medium theory allows us to correlate the normal state and paracoherent resistivities with the degree of texturization of samples. In particular, it is predicted that for non-textured samples the paracoherent resistivity should equal one third the normal state residual resistivity. Measurements on a batch of Y 1Ba 2Cu 3O 7 − δ granular samples are also presented to support, with no free parameters, our results.