Insulator-Superconductor Transition in 3D Granular Al-Ge Films

Abstract

We report the results of high magnetic field study of granular 3D Al-Ge and demonstrate that intragranular superconductivity leads in truly insulating samples (with an exponentially diverging normal state resistivity), either to a global superconducting phase coherent state, or to a ``superconductor-insulator'' state with Cooper pairs totally localized within individual grains, depending on the strength of the intergranular Josephson coupling.