American Physical Society
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.
R. P. Barber, Jr., S.-Y. Hsu, J. M. Valles, Jr., R. C. Dynes, and R. E. Glover, III. Negative magnetoresistance, negative electroresistance, and metallic behavior on the insulating side of the two-dimensional superconductor-insulator transition in granular Pb films. Phys. Rev. B 73, 134516 (2006)