Stringlike clusters and cooperative interlayer permeation in smectic liquid crystals formed by colloidal rods

Using simulations of hard rods in smectic-A states, we find stringlike clusters of up to 10 interlayer rods exhibiting dynamic cooperativity. We also find non-Gaussian diffusion and heterogeneous dynamics due to the equilibrium periodic smectic density profiles, which give rise to permanent barriers for layer-tolayer diffusion. This relaxation behavior is surprisingly similar to that of nonequilibrium supercooled liquids, although there the particles are trapped in transient (instead of permanent) cages