Topological Vortices Research Articles

Concentric ring optical traps for orbital rotation of particles

Abstract Optical vortices (OVs), as eigenmodes of optical orbital angular momentum, have been widely used in particle micro-manipulation. Recently, perfect optical vortices (POVs), a subclass of OVs, are gaining increasing interest and becoming an indispensable tool in optical trapping due to their unique property of topological charge-independent vortex radius. Here, we expand the concept of POVs by proposing concentric ring optical traps (CROTs) and apply them to trapping and rotating particles. A CROT consists of a series of concentric rings, each being a vortex whose radius and topological charge can be controlled independently with respect to the other rings. Quantitative results show that the generated CROTs have weak sidelobes, good uniformity, and relatively high diffraction efficiency. In experiments, CROTs are observed to trap multiple dielectric particles simultaneously on different rings and rotate these particles with the direction and speed of rotation depending on the topological charge sign and value of each individual ring. In addition, gold particles are observed to be trapped and rotate in the dark region between two bright rings. As a novel tool, CROTs may find potential applications in fields like optical manipulation and microfluidic viscosity measurements.

Electrically Controlling Vortices in a Neutral Exciton-Polariton Condensate at Room Temperature.

Manipulating bosonic condensates with electric fields is very challenging as the electric fields do not directly interact with the neutral particles of the condensate. Here we demonstrate a simple electric method to tune the vorticity of exciton-polariton condensates in a strong coupling liquid crystal (LC) microcavity with CsPbBr_{3} microplates as active material at room temperature. In such a microcavity, the LC molecular director can be electrically modulated giving control over the polariton condensation in different modes. For isotropic nonresonant optical pumping we demonstrate the spontaneous formation of vortices with topological charges of +1, +2, -2, and -1. The topological vortex charge is controlled by a voltage in the range of 1 to 10V applied to the microcavity sample. This control is achieved by the interplay of a built-in potential gradient, the anisotropy of the optically active perovskite microplates, and the electrically controllable LC molecular director in our system with intentionally broken rotational symmetry. Besides the fundamental interest in the achieved electric polariton vortex control at room temperature, our work paves the way to micron-sized emitters with electric control over the emitted light's phase profile and quantized orbital angular momentum for information processing and integration into photonic circuits.

Mechanical properties and abnormal mechanical behaviors of ferroelectric hexagonal manganites

Hexagonal manganites (h-RMnO3, R=Y, Ho-Lu) are emerging as advantageous multiferroic materials with structural ferroelectric topological defects. Strain has been proven as an effective means to control topological vortex cores. To further understand and utilize the mechanical manipulation mechanism, mechanical properties such as the Young’s modulus are important; however, accurate values are still to be obtained for single-crystalline specimens. In this study, by combining contact resonance atomic force microscopy, nanoindentation, and density functional theory calculations, we systematically studied the Young’s moduli of YMnO3, ErMnO3, and LuMnO3 single crystals. The Young's moduli of LuMnO3 obtained by the different methods were consistent, whereas for ErMnO3 and YMnO3, the abnormal mechanical behavior observed in the nanoindentation experiments deviated from the theoretical and experimental calculations. Through in-situ transmission electron microscopy, it was confirmed that lattice distortion plays a key role in resisting deformation, which is the origin of the abnormal mechanical behavior. Our work provides insights into an important mechanical parameter and the origin of the difference in the Young’s modulus of h-RMnO3, which is important for further theoretical investigations and potential applications.

Topological vortex mode for flexural waves in pillared plates

Localized topological modes with high robustness to various perturbations are receiving increasing attention. Recently, zero-order topological vortex modes have been designed in phononic structures, in analogy with zero-energy fermionic states modulated by Jackiw-Rossi binding mechanism. Such localized modes may have potential applications for biosensing, bioimaging and on-chip communication. In this work, we propose a pillared phononic plate with a Kekulé distortion of pillars position to bind topological modes at a vortex core via dispersion engineering. The phase winding and amplitude diagrams of the topological vortex mode are observed experimentally. It is found that existence of vibration peaks and corresponding mode patterns are strongly robust against the random perturbation of resonant frequencies of pillars at the vortex core. We further design a topological resonant sensor for mass sensitivity. The frequency of the topological vortex mode is almost linearly sensitive to added small mass at the vortex core in terms of mass values and positions. The proposed pillared plates provide a platform for potential applications such as energy localization and harvesting, remote health monitoring.

The emergence of three-dimensional chiral domain walls in polar vortices.

Chirality or handedness of a material can be used as an order parameter to uncovertheemergent electronic properties for quantum information science. Conventionally, chirality is found in naturally occurring biomolecules and magnetic materials. Chirality can be engineered in a topological polar vortex ferroelectric/dielectric system via atomic-scale symmetry-breaking operations. We use four-dimensional scanning transmission electron microscopy (4D-STEM) to map out thetopology-driven three-dimensional domain walls, where the handedness of two neighbor topological domains change or remain the same. The nature of the domain walls is governed by the interplay ofthe local perpendicular (lateral) and parallel (axial) polarization with respect to the tubular vortex structures. Unique symmetry-breaking operations and the finite nature of domain walls result in a triple pointformation at the junction of chiral and achiral domain walls. The unconventional nature of the domain walls with triple point pairs may result in unique electrostatic and magnetic properties potentially useful for quantum sensing applications.

Measuring the 3D wake of swimming snakes (Natrix tessellata) using volumetric particle image velocimetry.

We describe a method for measuring the 3D vortical structures produced by an anguilliform swimmer using volumetric velocimetry. The wake of freely swimming dice snakes (Natrix tessellata) was quantified, revealing the creation of multiple vortices along the body of the snake due to its undulation. The 3D structure of the vortices generally consisted of paired vortex tubes, some of which were linked together to form a hairpin structure. The observations match predictions from computational fluid dynamic studies of other anguilliform swimmers. Quantitative measurements allowed us to study vortex circulation and size, and global kinetic energy of the flow, which varied with swimming speed, vortex topology and individual characteristics. Our findings provide a baseline for comparing wake structures of snakes with different morphologies and ecologies and investigating the energetic efficiency of anguilliform swimming.

Universal visible emitters in nanoscale integrated photonics

Visible wavelengths of light control the quantum matter of atoms and molecules and are foundational for quantum technologies, including computers, sensors, and clocks. The development of visible integrated photonics opens the possibility for scalable circuits with complex functionalities, advancing both science and technology frontiers. We experimentally demonstrate an inverse design approach based on the superposition of guided mode sources, allowing the generation and complete control of free-space radiation directly from within a single 150 nm layer , showing low loss across visible and near-infrared spectra. We generate diverging circularly polarized beams at the challenging 461 nm wavelength that can be directly used for magneto-optical traps of strontium atoms, constituting a fundamental building block for a range of atomic-physics-based quantum technologies. Our generated topological vortex beams and the potential for spatially varying polarization emitters could open unexplored light–matter interaction pathways, enabling a broad new photonic–atomic paradigm. Our platform highlights the generalizability of nanoscale devices for visible-laser emission and will be critical for scaling quantum technologies.

Manipulating vortices with a rotating laser beam in Bose–Einstein condensates

We investigate the influence of a rotating laser beam on the dynamics of a topological vortex excitation in single-component and binary two-dimensional Bose–Einstein condensates loaded in harmonic traps. The vortex dynamics show different characters by considering the relative position of the vortex and the laser beam and the excitations in the condensates with respect to the rotating frequency and the size of the laser beam. We show the dynamic phase diagrams of single-component condensates with radial isotropy and anisotropy and binary condensates with the vortex and the laser beam being in the same component and different components. Interesting dynamical states such as bound-state, free-state, chaotic-state, free-chaotic-state and bound-chaotic-state are identified for different systems within certain parameter regions.

Helicity and topological charge tunable optical vortex based on a Hermite-Gaussian beam dynamically controlled folded-cavity resonator

Helicity and topological charge are two important characteristic parameters for vortex beam applications, including optical communications, optical manipulation and material processing, etc. In this work, a helicity and topological charge tunable vortex laser based on a folded resonant cavity is presented. In the resonant cavity, a Z-shaped structure is adopted and two deformable mirrors (DMs) are cascaded into the cavity as intro-cavity modulation elements. By applying different voltage combinations to the DMs, the Hermite-Gaussian (HG) beam with different indices and distribution orientations θ could be generated from the Z-shaped folded-cavity resonator. An extra-cavity astigmatic mode converter is adopted to convert the generated HG beam to the corresponding vortex beam with tunable helicity and topological charge, and the simulation results verified the feasibility of the presented vortex laser. In the experiment, the HGm,0θ beam (m = 1 to 10 and θ = −90 ° to 90 °]) and the vortex beam (topological charge l from ±1 to ±10 and left/right helicity) were flexibly achieved by simply adjusting the driving voltage combinations of the intra-cavity cascaded DMs.

Observation of Hidden Polar Phases and Flux Closure Domain Topology in Bi2WO6 Thin Films.

Topological textures of ferroelectric polarizations have promise as alternative devices for future information technology. A polarization rotation inevitably deviates from the stable orientation in axial ferroelectrics, but local energy losses compromise the global symmetry, resulting in a distorted shape of the topological vortex or inhibiting the vortex. Easy planar isotropy helps to promote rotating structures and, accordingly, to facilitate access to nontrivial textures. Here, we investigate the domain structure of an epitaxial thin film of bismuth tungsten oxide (Bi2WO6) grown on a (001) SrTiO3 substrate. By using angle-resolved piezoresponse force microscopy and scanning transmission electron microscopy, we find the existence of a hidden phase with ⟨100⟩-oriented ferroelectric polarizations in the middle of the four variant ⟨110⟩-oriented polarization domains, which assists in the formation of flux closure domains. The results suggest that this material is one step closer to becoming an isotropic two-dimensional polar material.

Uncovering polar vortex structures by inversion of multiple scattering with a stacked Bloch wave model

Nanobeam electron diffraction can probe local structural properties of complex crystalline materials including phase, orientation, tilt, strain, and polarization. Ideally, each diffraction pattern from a projected area of a few unit cells would produce a clear Bragg diffraction pattern, where the reciprocal lattice vectors can be measured from the spacing of the diffracted spots, and the spot intensities are equal to the square of the structure factor amplitudes. However, many samples are too thick for this simple interpretation of their diffraction patterns, as multiple scattering of the electron beam can produce a highly nonlinear relationship between the spot intensities and the underlying structure. Here, we develop a stacked Bloch wave method to model the diffracted intensities from thick samples with structure that varies along the electron beam. Our method reduces the large parameter space of electron scattering to just a few structural variables per probe position, making it fast enough to apply to very large fields of view. We apply our method to SrTiO3/PbTiO3/SrTiO3 multilayer samples, and successfully disentangle specimen tilt from the mean polarization of the PbTiO3 layers. We elucidate the structure of complex vortex topologies in the PbTiO3 layers, demonstrating the promise of our method to extract material properties from thick samples.

Collective transport and reconfigurable assembly of nematic colloids by light-driven cooperative molecular reorientations.

Nanomotors in nature have inspired scientists to design synthetic molecular motors to drive the motion of microscale objects by cooperative action. Light-driven molecular motors have been synthesized, but using their cooperative reorganization to control the collective transport of colloids and to realize the reconfiguration of colloidal assembly remains a challenge. In this work, topological vortices are imprinted in the monolayers of azobenzene molecules which further interface with nematic liquid crystals (LCs). The light-driven cooperative reorientations of the azobenzene molecules induce the collective motion of LC molecules and thus the spatiotemporal evolutions of the nematic disclination networks which are defined by the controlled patterns of vortices. Continuum simulations provide physical insight into the morphology change of the disclination networks. When microcolloids are dispersed in the LC medium, the colloidal assembly is not only transported and reconfigured by the collective change of the disclination lines but also controlled by the elastic energy landscape defined by the predesigned orientational patterns. The collective transport and reconfiguration of colloidal assemblies can also be programmed by manipulating the irradiated polarization. This work opens opportunities to design programmable colloidal machines and smart composite materials.

General theory on the growth kinetics of topological domain structure in hexagonal manganites

Although the dynamics of domain growth has been a long-standing topic in ferroic systems, its science complexity and important guidance to practical applications cannot be overemphasized. Highly anisotropic systems with only domain-wall-type defects and roughly isotropic systems with only vortex-type defects have been extensively studied as two ideal and extreme examples in terms of domain growth dynamics. The domain growth processes in these two types of systems are believed to follow two different scaling laws. The driving forces behind are domain wall motion and vortex–antivortex annihilation, respectively. However, no realistic ferroic systems have ever been found to exhibit a domain growth process that strictly follows these scaling laws. Fortunately, we now have a realistic ferroic system, i.e., the ferroelectric hexagonal manganite family in which the aforementioned two types of defects coexist. This system supports a fascinating topological vortex–antivortex domain structure and is a unique platform for probing a generalized theory on the domain growth dynamics that covers the two extremes. In this work, we investigate this vortex–antivortex domain structure and its growth dynamics within the framework of the Landau theory using phase-field simulations. It is revealed that morphology of this domain structure can be controlled by a correlation length Lc that is different from the conventional correlation length. More importantly, this domain structure can be seen as an intermediate state between the two extremes in terms of domain growth dynamics. When Lc is very small, the domain growth process in this domain structure is driven by domain wall motion and follows the well-known Allen–Cahn scaling law. As Lc increases, vortex–antivortex annihilation will dominate the domain growth process and the scaling law will need a logarithmical correction. The present work provides a comprehensive understanding of the domain growth behavior in such a realistic ferroic system of much attention and represents a substantial extension of domain growth dynamics toward complicated multi-defect systems.

Метод нейронных сетей для моделирования скирмионной решетки в композитном мультиферроике

Magnetoelectric nanofilms are of great interest as functional elements of ultra-dense memory cells. In the ground state they may contain various topological magnetic vortex structures of several nanometers in size. The qualitative and quantitative properties of such structures strongly depend on a set of physical parameters. To calculate the ground state configuration with given parameters, we use the steepest descent method; to study a large parametric space, however, significant computational resources are required. To solve this problem, we propose the use of artificial neural networks (ANN), which can help us uncover the relationship between combinations of parameters and the corresponding ground state configurations, using a relatively small number of pre-computed configurations as training data. The application of the ANN allows one to avoid excessive computational costs in the study of the parametric space and narrow down the parametric area in which the existence of stable non-trivial ground state configurations in the form of a stable skyrmion crystal is possible.

A snapshot of domain evolution between topological vortex and stripe in ferroelectric hexagonal ErMnO3

Hexagonal manganites exhibit three distinct domain patterns: stripe, loop, and vortex. Due to the high ferroelectric phase transition temperature and the lack of reliable visualization methods, it is still a mystery about the evolution and the formation of vortex networks. In this study, we managed to capture the coexistence of vortices, loops, and stripes by accurately controlling the annealing temperature right at Tc. We proposed a merging process between the V–AV pair and the stripe, which result in two different forms of vortex networks, namely, the normal vortex and the zigzag vortex. In addition, the connection between the density of stripes and the orientation of V–AV pairs is analyzed, which are both influenced by self-straining of the crystal. The mystery of evolution of the vortex network is unveiled by capturing the snapshot, and the experimental database provided calls for more analysis to understand the evolution of different domain topologies.

Topological vortex induced large recoverable electrostrain with high temperature-stability in ferroelectric nano-dots

Here we report by phase field simulations that in ferroelectric nanodots the single domain generated from the vortex under external electric field will transform back to the vortex structure after removal of the field, which could offer large recoverable electrostrain during the process. Moreover, it is found that the recoverable electrostrain maintains a large value and could exist over a wide temperature range. The good recoverability of the vortex structure and electrostrain in the ferroelectric nanodots is found to be mainly ascribed to the dipole-dipole interaction energy and the elastic interaction energy in the system. This work may shed light on the development of miniaturized actuators in Micro-Electro-Mechanical System (MEMS) or Nano-Electromechanical System (NEMS).

Arbitrarily polarized bound states in the continuum with twisted photonic crystal slabs

Arbitrary polarized vortex beam induced by polarization singularity offers a new platform for both classical optics and quantum entanglement applications. Bound states in the continuum (BICs) have been demonstrated to be associated with topological charge and vortex polarization singularities in momentum space. For conventional symmetric photonic crystal slabs (PhCSs), BIC is enclosed by linearly polarized far fields with winding angle of 2π, which is unfavorable for high-capacity and multi-functionality integration-optics applications. Here, we show that by breaking σz-symmetry of the PhCS, asymmetry in upward and downward directions and arbitrarily polarized BIC can be realized with a bilayer-twisted PhCS. It exhibits elliptical polarization states with constant ellipticity angle at every point in momentum space within the vicinity of BIC. The topological nature of BIC reflects on the orientation angle of polarization state, with a topological charge of 1 for any value of ellipticity angle. Full coverage of Poincaré sphere (i.e., - {{pi over 4}} le chi le {{pi over 4}} and - {{pi over 2}} le psi le {{pi over 2}}) and higher-order Poincaré sphere can be realized by tailoring the twist angles. Our findings may open up new avenues for applications in structured light, quantum optics, and twistronics for photons.

Vortex Structure Topology Analysis of the Transonic Rotor 37 Based on Large Eddy Simulation

Highly three–dimensional and complex flow structures are closely related to the aerodynamic losses occurring in the transonic axial–flow compressor. The large eddy simulation (LES) approach was adopted to study the aerodynamic performance of the NASA rotor 37 for the cases at the design, the near stall (NS), and the near choke (NC) flow rate. The internal flow vortex topology was analyzed by the Q–criterion method, the omega (Ω) vortex identification method, and the Liutex identification method. It was observed that the Q–criterion method was vulnerable to being influenced by the flow with high–shear deformation rate, especially near the end–wall regions. The Ω method was adopted to recognize the three–dimensional vortex structure with a higher precision than that of the Q–criterion method. Meanwhile, the Liutex vortex identification method showed a good performance in vortex identification, and the corresponding contribution of Liutex components in the vortex topology was analyzed. The results show that the high–vortex fields around the separation line and reattachment line had high vortex components in the x–axis, the tip clearance vortices presented a high–vortex component in the y–axis, and the suction side corner vortex possessed high–vortex components in the y– and z–axes.

Structural and Improper Ferroelectric Properties of TbInO3 Single Crystal Grown by Laser Floating Zone

The honeycomb TbInO3 has attracted wide research attention due to its fascinating physical properties. However, TbInO3 single crystal was difficult to grow owing to the high melting point and serious volatilization of indium during the crystal growth. In this study, the volatilization of the indium element was effectively suppressed by controlling the growth atmosphere and pressure. The excess ratio of indium oxide was determined, and pure hexagonal TbInO3 crystal was obtained by the laser floating zone method. Systematic studies on the crystal structure and optical and ferroelectric properties were carried out. The structure distortion resulted in the improper geometric ferroelectric revealed by single crystal diffraction and Raman spectrum measurements. The topological vortex domains and P-E hysteresis loop demonstrated the presence of ferroelectricity. TbInO3 crystal has great potential application in vortex memory.

Novel Geometric Ferroelectric EuInO3 Single Crystals with Topological Vortex Domains

RInO3 (R: rare-earth element) has drawn unprecedented research attention due to its geometric ferroelectricity and spin liquid state. However, the structure–property relationship needs further investigation based on well-developed single crystals. A EuInO3 crystal was obtained for the first time by the laser floating zone method. The presence of ferroelectricity was revealed by polarization–electric field hysteresis loops of the bulk EuInO3 single crystal. Moreover, interesting topological vortex domains were revealed by vertical piezoresponse force microscopy. The lattice dynamics of EuInO3 was probed by correlating various Raman modes with the structural distortion of the unit cell. The improper ferroelectricity and topological ferroelectric vortices of the EuInO3 crystal provide great potential for vortex memory devices.