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Dynamic Regimes for Driven Colloidal Particles on a Periodic Substrate at Commensurate and Incommensurate Fillings

We examine colloidal particles driven over a periodic muffin tin substrate using numerical simulations. In the absence of a driving force this system exhibits a rich variety of commensurate and incommensurate static phases in which topological defects can form domain walls, ordered stripes, superlattices, and disordered patchy regimes as a function of the filling fraction. When an external drive is applied, these different static phases generate distinct dynamical responses. At incommensurate fillings the flow generally occurs in the form of localized pulses or solitons correlated with the motion of the topological defect structures. We also find dynamic transitions between different types of moving states that are associated with changes in the velocity force curves, structural transitions in the topological defect arrangements, and modifications of the velocity distributions and particle trajectories. We find that the dynamic transitions between ordered and disordered flows exhibit hysteresis, while in strongly disordered regimes there is no hysteresis and the velocity force curves are smooth. When stripe patterns are present, transport can occur along the stripe direction rather than along the driving direction. Structural dynamic transitions can also occur within the pinned regimes when the applied drive causes distortions of the interstitially pinned particles while the particles trapped at pinning sites remain immobile.