Size Effects in Flow of Flux-Line Solids and Liquids

Flow of 2D flux lines confined to narrow channels has been studied. In the solid, (in)commensurability between lattice and channel width cause mobility oscillations from which the actual channel width follows. In the liquid, the oscillations disappear and flow is dictated by the shear viscosity $\eta$. By repeated experiments for different channel widths, $\eta$ is determined for the first time. It diverges according to $\eta \propto {\xi }_{+}^2(T,B)$. An indication for the hexatic-to-liquid transition is also observed.