Negative Magnetoresistance in Homogeneous Amorphous Superconducting Pb Wires

We report systematic magnetotransport measurements on a series of in situ grown homogeneous amorphous Pb wires. Corresponding to the broadening of the superconducting transitions as the wires cross over from 2D to 1D, we observe a negative magnetoresistance (MR) below the mean-field $T_c$ at low fields. Both the magnitude of the negative MR and the crossover field increase with decreasing $T_c$ and wire cross-sectional area. We speculate that these observations are the result of superfluid density fluctuations in sign as well as in magnitude along these wires close to the superconductor-insulator transition.