Coherence and Disorder in Arrays of Point Contacts

Abstract

By measuring the penetration depth and the critical current of three-dimensional assemblies of weakly coupled superconducting grains as a function of temperature, two critical exponents, $\ensuremath{\beta}$ and ${\ensuremath{\nu}}^{\ensuremath{'}}$, were determined characterizing the transition to coherence of the system. As in calculations on disordered systems, strict universality does not hold, but the exponents are shown to be compatible with the hypothesis of weak universality.