Negative magnetoresistance, negative electroresistance, and metallic behavior on the insulating side of the two-dimensional superconductor-insulator transition in granular Pb films

Granular Pb thin films on the insulating side of the two-dimensional superconductor-insulator transition are observed to exhibit a large negative magnetoresistance and electroresistance (change in resistance with electric field) at low temperatures. At high measurement voltages and low temperatures, the film resistances become temperature independent creating a "metallic" state. These phenomena are explained as manifestations of transport due to intergranular quasiparticle tunneling. This explanation might also provide insights into the similar behavior observed in other superconductors.