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.

Controlled trapping and guided motion of vortices via special arrangements of microholes, so-called antidots, in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ 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.

A thermodynamically stable vortex-antivortex pattern has been revealed in equilateral mesoscopic type I superconducting triangles, contrary to type II superconductors where similar patterns are unstable. The stable vortex-antivortex “molecule” appears due to the interplay between two factors: a repulsive vortex-antivortex interaction in type I superconductors and the vortex confinement in the mesoscopic triangle.

We study the critical depinning current $J_c$ 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 $J_c(\Phi )$ are determined by a sequence of harmonics of the long and short segments of the chain. The critical current $J_c(\Phi )$ has a remarkable self-similarity. In 2D QP pinning arrays, we predict analytically and numerically the main features of $J_c(\Phi )$, and demonstrate that the Penrose lattice of pinning sites provides an enormous enhancement of $J_c(\Phi )$, even compared to triangular and random pinning site arrays. This huge increase in $J_c(\Phi )$ could be useful for applications.

Merged, or giant, multiquanta vortices (GVs) are known to appear in very small superconductors near the superconducting transition due to strong confinement of magnetic flux. Here we present evidence for a new, pinning-related, mechanism for vortex merger. Using Bitter decoration to visualize vortices in small Nb disks with varying degrees of disorder, we show that confinement in combination with strong disorder causes individual vortices to merge into clusters or even GVs well below $T_c$ and $H_{c2}$, in contrast to well-defined shells of individual vortices found in the absence of pinning.

We study the critical depinning current $J_c$, as a function of the applied magnetic flux $\Phi$, for quasiperiodic (QP) pinning arrays, including one-dimensional (1D) chains and two-dimensional (2D) arrays of pinning centers placed on the nodes of a fivefold Penrose lattice. In 1D QP chains of pinning sites, the peaks in $J_c\left(\Phi \right)$ are shown to be determined by a sequence of harmonics of long and short periods of the chain. This sequence includes as a subset the sequence of successive Fibonacci numbers. We also analyze the evolution of $J_c\left(\Phi \right)$ while a continuous transition occurs from a periodic lattice of pinning centers to a QP one; the continuous transition is achieved by varying the ratio $\gamma =a_S∕a_L$ of lengths of the short $a_S$ and the long $a_L$ segments, starting from $\gamma =1$ for a periodic sequence. We find that the peaks related to the Fibonacci sequence are most pronounced when $\gamma$ is equal to the “golden mean.” The critical current $J_c\left(\Phi \right)$ in a QP lattice has a remarkable self-similarity. This effect is demonstrated both in real space and in reciprocal $k$ space. In 2D QP pinning arrays (e.g., Penrose lattices), the pinning of vortices is related to matching conditions between the vortex lattice and the QP lattice of pinning centers. Although more subtle to analyze than in 1D pinning chains, the structure in $J_c\left(\Phi \right)$ is determined by the presence of two different kinds of elements forming the 2D QP lattice. Indeed, we predict analytically and numerically the main features of $J_c\left(\Phi \right)$ for Penrose lattices. Comparing the $J_c$’s for QP (Penrose), periodic (triangular) and random arrays of pinning sites, we have found that the QP lattice provides an unusually broad critical current $J_c\left(\Phi \right)$, that could be useful for practical applications demanding high $J_c$’s over a wide range of fields.