  In the wake of previous studies on the rattling-and-jumping diffusion in
smectic liquid crystal phases of colloidal rods, we analyze here for the first
time the heterogeneous dynamics in columnar phases. More specifically, we
perform computer simulations to investigate the relaxation dynamics of a binary
mixture of perfectly aligned hard spherocylinders. We detect that the columnar
arrangement of the system produces free-energy barriers the particles should
overcome to jump from one column to another, thus determining a hopping-type
diffusion. This phenomenon accounts for the non-Gaussian inter-column diffusion
and shows a two-step structural relaxation which is remarkably analogous to
that of out-of-equilibrium glass-forming systems and gels. Surprisingly enough,
slight deviations from the behavior of simple liquids due to transient cages is
also observed in the direction perpendicular to this plane, where the system is
usually referred to as liquid-like.
