Directional Locking

Particles which are driven across periodic substrate potentials show a number of intriguing phenomena. Depending on the direction of the applied driving force F, the orientation of the particle's motion can substantially deviate from F but is locked-in to directions determined by the substrate's symmetry. Examples of such kinetically locked-in states range from atom migration on crystalline surfaces, driven charge density waves to flux flow in type-II superconductors. Also, it has been demonstrated that directional locking can be employed for sorting of colloidal particles according to their size, refractive index or chirality. When subjecting a monolayer of colloidal particles to quasiperiodic substrates potentials being created by interfering laser beams, we also observe dynamical ordering with a pronounced colloidal smectic phase. This suggests that dynamical ordering is not restricted to periodic potentials but also occurs under more general conditions.

Further information

Experimental Observation of Directional Locking and Dynamical Ordering of Colloidal Monolayers Driven across Quasiperiodic Substrates
Thomas Bohlein, and Clemens Bechinger
Phys. Rev. Lett. 109, 058301 (2012)