Brownian transport of self-propelled overdamped microswimmers (like Janus particles) in a two-dimensional periodically compartmentalized channel is numerically investigated for different compartment geometries, boundary collisional dynamics, and particle rotational diffusion. The resulting time-correlated active Brownian motion is subject to rectification in the presence of spatial asymmetry. We prove that ratcheting of Janus particles can be orders of magnitude stronger than for ordinary thermal potential ratchets and thus experimentally accessible. In particular, autonomous pumping of a large mixture of passive particles can be induced by just adding a small fraction of Janus particles.
We study the critical depinning current Jc versus the applied magnetic flux Phi, for quasiperiodic (QP) chains and 2D arrays of pinning centers placed on the nodes of a fivefold Penrose lattice. In QP chains, the peaks in Jc(Phi) are determined by a sequence of harmonics of the long and short segments of the chain. The critical current Jc(Phi) has a remarkable self-similarity. In 2D QP pinning arrays, we predict analytically and numerically the main features of Jc(Phi), and demonstrate that the Penrose lattice of pinning sites provides an enormous enhancement of Jc(Phi), even compared to triangular and random pinning site arrays. This huge increase in Jc(Phi) could be useful for applications.
Controlled trapping and guided motion of vortices via special arrangements of microholes, so-called antidots, in YBa 2 Cu 3 O 7 films and devices is demonstrated. Resistive Hall-type measurements prove the presence of guided flux motion along rows of antidots. In contrast to conventional vortex motion due to vortex unpinning at currents exceeding the critical current, this motion is present down to zero current and low temperatures. It is characterized by a linear voltage-current dependence, i.e., Ohmic behavior. The latter is indicative for a novel mechanism of vortex propagation that is probably based upon flux nucleation within antidots due to the redistribution of screening currents and flux quantization. Together with trapping of vortices by isolated antidots this mechanism can be used for new devices concepts. As an example a vortex ratchet formed by a special arrangement of antidots is demonstrated.
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