Geometry dependent dephasing in small metallic wires

Temperature dependent weak localization is measured in metallic nanowires in a previously unexplored size regime down to width $w=5$ nm. The dephasing time, ${\tau }_{\varphi }$, shows a low temperature $T$ dependence close to quasi-1D theoretical expectations (${\tau }_{\varphi }\sim T^{-2\mathrm{/}3}$) in the narrowest wires, but exhibits a relative saturation as $T\to 0$ for wide samples of the same material, as observed previously. As only sample geometry is varied to exhibit both suppression and divergence of ${\tau }_{\varphi }$, this finding provides a new constraint on models of dephasing phenomena.