Quasi-Equilibrium Dynamics and Non-Debye Relaxation in High Tc Granular Superconductors

Abstract

High Tc granular superconductors are concrete examples of 3D disordered arrays of coupled junctions. While their static critical properties have been studied to some extent1–2, the study of their critical dynamics properties is still an open subject and it is made difficult by the existence of both intergranular and intragranular junctions3. The difficulty stands in the overlapping between the dynamically-relevant temperature ranges of the two types of junctions. Being mainly interested in the physics of the intergranular connections, we were forced to develop first of all a procedure to select the range of the experimental parameters in such a way to disentangle their own features, as described in ref.3. Our main concern here is devoted to the quasi-equilibrium dynamics of the junction system, that is, the dynamics that can be studied in a situation of uniform magnetic field penetration. By means of a careful examination of the a.c. (both linear and non-linear) susceptibility data, we have recently shown that it is possible to define a temperature range within which the critical dynamics is typical of a fully-pierced intergranular network3. In the recent past, there has been an explosive growth in the number of works dealing with the a.c. susceptibility of the high Tc granular samples, and the interpretations of the experimental data are thereupon spread and suffer of the school of thinking to which each researcher belongs. We can separate them at least in two groups whose opinions are not really in contrast between them but, we believe, rather focused on two different dynamical behaviours: the non-equilibrium4 and the quasi-equilibrium ones5,1. The first group of researchers (whithin which we may distinguish between those that regard the “intergranular matter” as a standard type-II superconductor and those that consider it as a true ensemble of junctions) prefers to cope with those aspects of the dynamics experimentally relevant when the sample is inhomogeneously pierced by the a.c. magnetic field.KeywordsSpin GlassFractal ClusterCritical DynamicCritical State ModelJunction NetworkThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.