Suppression of superconductivity dominated by proximity effect in amorphous MoSi nanobelts

A traditional concept proposes that the suppression of the transition temperature Tc in an amorphous nanobelt is driven by enhanced disorder, which accounts for localized Cooper pairs. However, in this paper, we observe Tc suppression in an amorphous molybdenum-silicide (MoSi) nanobelt, which scales as the inverse square of the width but contradicts disorder theory. Instead, the transition regime can be well described by Cooper pair diffusion in the proximity effect. Both the nonlinear reduction of the switching current density and the abnormal increase of the effective retrapping current density with the reduction of the width further verify the proximity-induced relation. Therefore, we attribute the main size dependence of the suppressed superconducting properties in the MoSi nanobelt to the proximity effect rather than disorder. We speculate that the competition between superconductivity and disorder only appears at the two narrow edge bands rather than the entire nanobelt. Subsequently, the reduction in width does not produce a significant impact on superconductivity for disorder, and only the proximity effect plays an overwhelming role in the MoSi nanobelt.