Magnetoresistance oscillations in granular Sn wires near the superconductor-insulator transition

We report on a series of magnetoresistance measurements of in situ grown granular Sn wires with widths from 1100-2000 Angstrom. The magnetoresistance is measured within the superconducting resistive transition of wires with different normal state resistances and the results are compared to two-dimensional (2D) granular Sn films. Both the wires and the 2D films exhibit two distinct magnetic-field regimes: a low-field weak positive magnetoresistance regime and a high-field strong positive magnetoresistance regime. In addition, the wires exhibit strong reproducible magnetoresistance oscillations within the low-field regime near the superconductor-insulator transition, which are not observed in the 2D films. We attribute these magnetoresistance oscillations to the effects of screening currents circulating around phase coherent loops of weakly linked superconducting grains. The observed magnetoresistance at different field strengths in the wires and films allows for a clear and coherent interpretation of the mechanisms causing the magnetoresistance behavior, and the magnetic-field tuned superconductor-insulator transition. [S0163-1829(98)00646-8].