Suppression of superconductivity in low dimensional systems: Effects of magnetic impurities in Molybdenum-Germanium films and superconductor-insulator transition in long Molybdenum-Germanium nanowires

In the first three chapters of this dissertation, we report experimental measurements of pair breaking strength per magnetic Gd atoms on amorphous superconducting MoGe films with thickness in the range of 1-50nm. The strength of a magnetic pair breaker monotonically decreases with decreasing film thickness and becomes almost zero for the superconducting film with Tc ≈ 1K. Suppression of superconductivity by reducing film thickness and by magnetic impurities is observed to be a nonadditive processes in amorphous MoGe alloy. The anomalous behavior is likely related to inhomogeneous distribution of the order parameter.;In the last four chapters, we present the experimental results of the transport properties for two series of long (1-25mum) and very narrow (9-20 nm) homogenous amorphous MoGe wires fabricated by advanced electron beam lithography. We observed that wires undergo a superconducting-insulator transition that is controlled by cross-sectional area of a wire, i.e., by local physics. Mean-field critical temperature (Tc) decreases exponentially with a wire cross section, suggesting that the reduction in Tc is likely fermionic due to the enhancement of Coulomb repulsion. After losing superconductivity, the resistance of the wires increases monotonically with decreasing temperature and shows a conductance dip at zero-bias voltage. This zero-bias anomaly in insulating wires has the signature of both Coulomb blockade and perturbative electron-electron interaction correction in one-dimensional system.