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Four iron-based triple tungstate and tellurate perovskites have been synthesized in the nanocrystalline form using a simple sol–gel citrate route: Sr3Fe2WO9 (SFWO), Ba3Fe2WO9 (BFWO), Sr3Fe2TeO9 (SFTO), and Ba3Fe2TeO9 (BFTO). Strontium-based compounds crystallize in the tetragonal space group I4/m, while barium-based compounds crystallize in the hexagonal space group P63/mmc. All compounds possess a ferromagnetic order with high values for room-temperature magnetization. The magnetic state as traced by Mo¨ssbauer spectroscopy is heterogeneously related to disorder. The compounds also possess relatively high dielectric constants (20–199.16) measured at 1 MHz and a moderate loss factor. The synthesized triple perovskite compounds were utilized in the fabrication of vertical contact mode triboelectric nanogenerators (TENGs). The working mechanism and the electrical response of the TENGs were extensively studied. The TENG device based on BFTO/Kapton triboelectric layers produces the highest output of 88 V/2.69 mA. For the first time, the surface polarity of the triple perovskite was shown using a Kelvin probe force microscopy technique (KPFM), which elucidates the positive polarity of the triboelectric layer. Furthermore, the TENG device was used to charge several capacitors and to carry out the powering of electronics that make it an excellent choice for various self-powered applications.

Liquid crystals (LCs) can host robust topological defect structures that essentially determine their optical and elastic properties. Although recent experimental progress enables precise control over localization and dynamics of nematic LC defects, their practical potential for information storage and processing has yet to be explored. Here, we introduce the concept of nematic bits (nbits) by exploiting a quaternionic mapping from LC defects to the Poincar\'e-Bloch sphere. Through theory and simulations, we demonstrate how single-nbit operations can be implemented using electric fields, in close analogy with Pauli, Hadamard and other common quantum gates. Ensembles of two-nbit states can exhibit strong statistical correlations arising from nematoelastic interactions, which can be used as a computational resource. Utilizing nematoelastic interactions, we show how suitably arranged 4-nbit configurations can realize universal classical NOR and NAND gates. Finally, we demonstrate the implementation of generalized logical functions that take values on the Poincar\'e-Bloch sphere. These results open a new route towards the implementation of classical and non-classical computation strategies in topological soft matter systems., Comment: title updated; introduction extended; nbit realizations of universal NAND and NOR gates and generalized logic functions added in new Figures 6 and 7

We propose the Sachdev-Ye-Kitaev Lindbladian as a paradigmatic solvable model of dissipative many-body quantum chaos. It describes N strongly coupled Majorana fermions with random all-to-all interactions, with unitary evolution given by a quartic Hamiltonian and the coupling to the environment described by M quadratic jump operators, rendering the full Lindbladian quartic in the Majorana operators. Analytical progress is possible by developing a dynamical mean-field theory for the Liouvillian time evolution on the Keldysh contour. By disorder-averaging the interactions, we derive an (exact) effective action for two collective fields (Green’s function and self-energy). In the large-N, large-M limit, we obtain the saddle-point equations satisfied by the collective fields, which determine the typical timescales of the dissipative evolution, particularly the spectral gap that rules the relaxation of the system to its steady state. We solve the saddle-point equations numerically and find that, for strong or intermediate dissipation, the system relaxes exponentially, with a spectral gap that can be computed analytically, while for weak dissipation, there are oscillatory corrections to the exponential relaxation. In this letter, we illustrate the feasibility of analytical calculations in strongly correlated dissipative quantum matter.

Soavtorji: Tilen Potisk, Matej Praprotnik, Daniel Svenšek. Bibliografija: str. 224317-13-224317-14. Abstract.

In liquid crystal applications, boundary conditions are essential to ensuring suitable bulk molecular orientation and a deterministic response to external fields. Be it confinement to a droplet or a shell, a glass plate, or an interface with air or another liquid, proper surface alignment must be ensured&mdash, mechanically by rubbing, by chemical treatment that adds a layer of aligning molecules, by using photoalignment or even by leaving the surface untreated, using the intrinsic properties of the substrate itself. The anchoring can be classified as unidirectional (perpendicular homeotropic, or at oblique angles), or degenerate (planar or pre-tilted). However, if both substances at the interface are anisotropic, more diverse behaviour is expected. Here, we present a numerical simulation of a nematic droplet in a nematic host, and investigate behaviour of the director field and defects at the interface for different interfacial couplings. Finally, we compare the simulations to experimental images of discotic droplets in a calamitic nematic host.

Quasicrystalline ordering was first observed in synthetic multi-component metallic alloys. These solid state materials exhibit quasicrystalline atomic ordering at nanometer length scales. Softmatter systems are another class of versatile materials that can exhibit quasicrystalline ordering across supra-nanometer (&gt, 10 nm) to supra-micrometer (&gt, 10 &mu, m) length scales as recently observed in materials like-supramolecular dendritic molecules, ABC star polymers, binary nanoparticle systems and block co-polymers in condensed matter systems. The underlying mechanism in most of these soft quasicrystals seems to be the presence of two or more length scales in the system. Another class of development in self-assembled quasicrystals in softmatter is being observed in low molecular weight chiral and achiral nematic liquid crystals. Liquid crystal forms an efficient matrix for self- and directed-assemblies of colloidal structures where surface and geometry-tuning the particles in nematic liquid crystals gives rise to complex inter-particle interactions while the long-range order results in self-assembled structures of higher order rotational symmetries. Furthermore, there has also been attempts to generate colloidal quasicrystalline defect structures by directing the assemblies using multiple and single beam lasing techniques. In the present article, we will review self- and assisted-assembly of quasicrystalline structures in nematic liquid crystals (both chiral and achiral) and discuss the underlying mechanisms.

Active nematics contain topological defects which under sufficient activity move, create and annihilate in a chaotic quasi-steady state, called active turbulence. However, understanding active defects under confinement is an open challenge, especially in three-dimensions. Here, we demonstrate the topology of three-dimensional active nematic turbulence under the spherical confinement, using numerical modelling. In such spherical droplets, we show the three-dimensional structure of the topological defects, which due to closed confinement emerge in the form of closed loops or surface-to-surface spanning line segments. In the turbulent regime, the defects are shown to be strongly spatially and time varying, with ongoing transformations between positive winding, negative winding and twisted profiles, and with defect loops of zero and non-zero topological charge. The timeline of the active turbulence is characterised by four types of bulk topology-linked events --- breakup, annihilation, coalescence and cross-over of the defects --- which we discuss could be used for the analysis of the active turbulence in different three-dimensional geometries. The turbulent regime is separated by a first order structural transition from a low activity regime of a steady-state vortex structure and an offset single point defect. We also demonstrate coupling of surface and bulk topological defect dynamics by changing from strong perpendicular to inplane surface alignment. More generally, this work is aimed to provide insight into three-dimensional active turbulence, distinctly from the perspective of the topology of the emergent three-dimensional topological defects., Comment: 7 figures

Droplets of active fluid form a dynamically self-assembled material based on the cross-talk between active and passive defects., The formation of emulsions from multiple immiscible fluids is governed by classical concepts such as surface tension, differential chemical affinity and viscosity, and the action of surface-active agents. Much less is known about emulsification when one of the components is active and thus inherently not constrained by the laws of thermodynamic equilibrium. We demonstrate one such realization consisting in the encapsulation of an active liquid crystal (LC)–like gel, based on microtubules and kinesin molecular motors, into a thermotropic LC. These active nematic emulsions exhibit a variety of dynamic behaviors that arise from the cross-talk between topological defects separately residing in the active and passive components. Using numerical simulations, we show a feedback mechanism by which active flows continuously drive the passive defects that, in response, resolve the otherwise degenerated trajectories of the active defects. Our experiments show that the choice of surfactant, which stabilizes the active/passive interface, allows tuning the regularity of the self-sustained dynamic events. The hybrid active-passive system demonstrated here provides new perspectives for dynamic self-assembly driven by an active material but regulated by the equilibrium properties of the passive component.

Physically intelligent micro-robotic systems exploit information embedded in micro-robots, their colloidal cargo, and their milieu to interact, assemble, and form functional structures. Nonlinear anisotropic fluids such as nematic liquid crystals (NLCs) provide untapped opportunities to embed interactions via their topological defects, complex elastic responses, and ability to dramatically restructure in dynamic settings. Here a four-armed ferromagnetic micro-robot is designed and fabricated to embed and dynamically reconfigure information in the nematic director field, generating a suite of physical interactions for cargo manipulation. The micro-robot shape and surface chemistry are designed to generate a nemato-elastic energy landscape in the domain that defines multiple modes of emergent, bottom-up interactions with passive colloids. Micro-robot rotation expands the ability to sculpt interactions the energy landscape around a rotating micro-robot is dynamically reconfigured by complex far-from-equilibrium dynamics of the micro-robot’s companion topological defect. These defect dynamics allow transient information to be programmed into the domain and exploited. Robust micro-robotic manipulation strategies are demonstrated that exploit these diverse modes of nemato-elastic interaction to achieve cargo docking, transport, release, and assembly of complex reconfigurable structures at multi-stable sites. Such structures are of great interest to future developments of LC-based advanced optical device and micro-manufacturing in anisotropic environments.

Charge profiles in liquid electrolytes are of crucial importance for applications, such as supercapacitors, fuel cells, batteries, or the self-assembly of particles in colloidal or biological settings. However, creating localised (screened) charge profiles in the bulk of such electrolytes, generally requires the presence of surfaces -- for example, provided by colloidal particles or outer surfaces of the material -- which poses a fundamental constraint on the material design. Here, we show that topological defects in nematic electrolytes can perform as regions for local charge separation, forming charged defect cores and in some geometries even electric multilayers, as opposed to the electric double layers found in isotropic electrolytes. Using a Landau-de Gennes-Poisson-Boltzmann theoretical framework, we show that ions highly effectively couple with the topological defect cores via ion solvability, and with the local director-field distortions of the defects via flexoelectricity. The defect charging is shown for different defect types -- lines, points, and walls -- using geometries of ionically screened flat isotropic-nematic interfaces, radial hedgehog point defects and half-integer wedge disclinations in the bulk and as stabilised by (charged) colloidal particles. More generally, our findings are relevant for possible applications where topological defects act as diffuse ionic capacitors or as ionic charge carriers., Comment: 16 pages, 11 figures. V2: Added discussion and paragraph on experimental relevance

We investigate the nonequilibrium response of quasiperiodic systems to boundary driving. In particular we focus on the Aubry-Andr\'e-Harper model at its metal-insulator transition and the diagonal Fibonacci model. We find that opening the system at the boundaries provides a transparent and experimentally viable technique to probe its underlying fractality, which is reflected in the fractal spatial dependence of simple observables (such as magnetization) in the nonequilibrium steady state. We also find that the dynamics in the nonequilibrium steady state depends on the length of the chain chosen: generic length chains harbour qualitatively slower transport (different scaling exponent) than Fibonacci length chains, which is in turn slower than in the closed system. We conjecture that such fractal nonequilibrium steady states should arise in generic driven critical systems that have fractal properties., Comment: 2 column format, 4+5.5+1 pages, 4+10 figures; v2 has more broccoli inside: further support for (i) fractality and scaling of various transport + steady state measures in generalized Fibonacci sequences, (ii) contrast between open vs. closed system dynamics