Experimental observation of directional locking and dynamical ordering of colloidal monolayers driven across quasiperiodic substrates.

We experimentally investigate the structural behavior of an interacting colloidal monolayer being driven across a decagonal quasiperiodic potential landscape created by an optical interference pattern. When the direction of the driving force is varied, we observe the monolayer to be directionally locked on angles corresponding to the symmetry axes of the underlying potential. At such locking steps, we observe a dynamically ordered smectic phase in agreement with recent simulations. We demonstrate that such dynamical ordering is due to the interaction of particle lanes formed by interstitial and noninterstitial particles.