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.

The research field of man-made nano/micromotors is growing significantly at the level of new materials and fabrication, as well as numerous exciting demonstrations, ranging from Visible light-driven nano/micromotors are promising candidates for biomedical and environmental applications. This study demonstrates blue light-driven Ag/AgCl-based spherical Janus micromotors, which couple plasmonic light absorption with the photochemical decomposition of AgCl. These micromotors reveal high motility in pure water, i.e., mean squared displacements (MSD) reaching 800 µm 2 within 8 s, which is 100× higher compared to previous visible light-driven Janus micromotors and 7× higher than reported ultraviolet (UV) light-driven AgCl micromotors. In addition to providing design rules to realize efficient Janus micromotors, the complex dynamics revealed by individual and assemblies of Janus motors is investigated experimentally and in simulations. The effect of suppressed rotational diffusion is focused on, compared to UV light-driven AgCl micromotors, as a reason for this remarkable increase of the MSD. Moreover, this study demonstrates the potential of using visible light-driven plasmonic Ag/AgCl-based Janus micromotors in human saliva, phosphate-buffered saline solution, the most common isotonic buffer that mimics the environment of human body fluids, and Rhodamine B solution, which is a typical polluted dye for demonstrations of photocatalytic environmental remediation. This new knowledge is useful for designing visible light driven nano/micromotors based on the surface plasmon resonance effect and their applications in assays relevant for biomedical and ecological sciences. Janus Micromotors

Multi-quanta, or giant, 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 the formation of GVs. Using Bitter decoration to visualise vortices in small Nb disks, 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.Mesoscopic superconductors, i.e., such that they can accommodate only a small number of vortices, are known to exhibit complex and unique vortex structures due to the competition between surface superconductivity and vortex-vortex interactions [see e.g. 1-6]. For mesoscopic disks, theoretical studies found two kinds of superconducting states: a giant vortex (GV), i.e., a circular symmetric state with a fixed value of angular momentum that can carry several flux quanta [1,2] and multivortex states (MVS) with an effective total angular momentum corresponding to the number of vortices in the disk (vorticity L) [3]. Recently, it became possible to experimentally distinguish between a singlecore GV and a MVS composed of singly quantized vortices using the multiple-small-tunnel-junction

We study the critical depinning current Jc, as a function of the applied magnetic flux Φ, for quasiperiodic (QP) pinning arrays, including one-dimensional (1D) chains and two-dimensional (2D) arrays of pinning centers placed on the nodes of a five-fold Penrose lattice. In 1D QP chains of pinning sites, the peaks in Jc(Φ) 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 Jc(Φ) 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 γ = aS/aL of lengths of the short aS and the long aL segments, starting from γ = 1 for a periodic sequence. We find that the peaks related to the Fibonacci sequence are most pronounced when γ is equal to the "golden mean". The critical current Jc(Φ) in 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 Jc(Φ) 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 Jc(Φ) for Penrose lattices. Comparing the Jc'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 Jc(Φ), that could be useful for practical applications demanding high Jc's over a wide range of fields.

Molecular diffusion in unidimensional channel structures (single-file diffusion) is important to understand the behavior of, e.g., colloidal particles in porous materials (zeolites) and superconducting vortices in 1-dimensional (1D) channels. Here the diffusion of charged massive particles in a 1D channel is investigated using the Langevin Dynamics (LD) simulations. We analyze different regimes based on the hierarchy of the interactions and damping mechanisms in the system and we show that, contrary to previous findings, single-file diffusion depends on the inter-particle interaction and could be suppressed if the interaction is strong enough displaying a subdiffusive behavior slower than t 1/2 , in agreement with recent experimental observations in colloids and charged metallic balls.

Quasiperiodic pinning arrays, as recently demonstrated theoretically and experimentally using a fivefold Penrose tiling, can lead to a significant enhancement of the critical current I c as compared to "traditional" regular pinning arrays. However, while regular arrays showed only a sharp peak in I c ͑⌽͒ at the matching flux ⌽ 1 and quasiperiodic arrays provided a much broader maximum at ⌽Ͻ⌽ 1 , both types of pinning arrays turned out to be inefficient for fluxes larger than ⌽ 1 . We demonstrate theoretically and experimentally the enhancement of I c ͑⌽͒ for ⌽Ͼ⌽ 1 by using non-Penrose quasiperiodic pinning arrays. This result is based on a qualitatively different mechanism of flux pinning by quasiperiodic pinning arrays and could be potentially useful for applications in superconducting microelectronic devices operating in a broad range of magnetic fields.