Observation of localized magnetic plasmon skyrmions

Cluster analysis as a tool for quantifying structure-transport properties in simulations of superconcentrated electrolyte

Using molecular dynamics simulations and graph-theory-based cluster analysis, we investigate the structure-transport properties of typical water-in-salt electrolytes. We demonstrate that ions exhibit distinct dynamics across different ionic clusters-namely, solvent-separated ion pairs (SSIPs), contact ion pairs (CIPs), and aggregates (AGGs). We assess the average proportions of various ionic species and their lifetimes. Our method reveals a dynamic decoupling of ion kinetics, with each species independently contributing to the overall molecular motion. This is evidenced by the fact that the total velocity autocorrelation function (VACF) and power spectrum can be expressed as a weighted sum of independent functions for each species. The experimental data on the ionic conductivity of the studied LiTFSI electrolytes align well with our theoretical predictions at various concentrations, based on the proportions and diffusion coefficients of free ions derived from our analysis. The insights gained into the solvation structures and dynamics of different ionic species enable us to elucidate the physical mechanisms driving ion transport in such superconcentrated electrolytes, providing a comprehensive framework for the future design and optimization of electrolytes.

Ag-modified enhance the performances of ZnO@CFs based omnidirectional photoelectrochemical ultraviolet detectors

There are several prospective applications for omnidirectional ultraviolet (UV) detectors and underwater detection detectors in optical systems and optical fields. In this work, ZnO nanorods arrays were grown on carbon fibers (CFs). An appropriate amount of Ag nanoparticles (NPs) was deposited on the surface of ZnO nanorods by photochemical deposition. This improved the performance of photoelectrochemical (PEC) based UV detectors. Under 365 nm and 10 mW cm-2UV irradiation, the photocurrent density of the 30s-Ag/ZnO@CFs based PEC UV detector can reach 1.28 mA cm-2, which is about 7 times that of the ZnO@CFs based PEC UV detector, and the rising time is shortened from 0.17 to 0.10 s. The reason is that increased absorption of ultraviolet light induced by the localized surface plasmon resonance. In addition, the detector exhibits a good flexibility and remains flexible after hundreds of bends and twists. Moreover, the detector is responsive in the range of rotation angle from 0° to 360°. It provides an insight to improve the photoelectric performance and underwater omnidirectional detection ability of the PEC UV detector.

Are SAXS and SANS suitable to extract information on the role of water for electric-double-layer formation at the carbon-aqueous-electrolyte interface?

This study reports on the applicability of X-ray transmission (XRT), small- and wide-angle X-ray scattering (SAXS/WAXS) and small-angle neutron scattering (SANS) for investigating fundamental processes taking place in the working electrode of an electric double-layer capacitor with 1 M RbBr aqueous electrolyte at different applied potentials. XRT and incoherent neutron scattering are employed to determine global ion- and water-concentration changes and associated charge-balancing mechanisms. We showcase the suitability of SAXS and SANS, respectively, to get complementary information on local ion and solvent rearrangement in nanoconfinement, but also underscore the limitations of simple qualitative models, asking for more quantitative descriptions of water-water and ion-water interactions via detailed atomistic modelling approaches.

Water-Wave Vortices and Skyrmions

Topological wave structures-phase vortices, skyrmions, merons, etc.-are attracting enormous attention in a variety of quantum and classical wave fields. Surprisingly, these structures have never been properly explored in the most obvious example of classical waves: water-surface (gravity-capillary) waves. Here, we fill this gap and describe (i) water-wave vortices of different orders carrying quantized angular momentum with orbital and spin contributions, (ii) skyrmion lattices formed by the instantaneous displacements of the water-surface particles in wave interference, and (iii) meron (half-skyrmion) lattices formed by the spin-density vectors, as well as (iv) spatiotemporal water-wave vortices and skyrmions. We show that all these topological entities can be readily generated in linear water-wave interference experiments. Our findings can find applications in microfluidics and show that water waves can be employed as an attainable playground for emulating universal topological wave phenomena.

Topological state transitions of skyrmionic beams under focusing configurations

The recent emerging appearance of optical analogs of magnetic quasiparticles, i.e., optical skyrmions constructed via spin, field, and Stokes vectors, has garnered substantial interest from deep-subwavelength imaging and quantum entanglement. Here, we investigate systematically the topological state transitions of skyrmionic beams constructed by the Stokes vectors in the focusing configuration. We theoretically demonstrated that in the weak focusing, the skyrmion topological number is protected. Whereas, in the tight focusing, a unique topological transformation with skyrmion number variation is exhibited for the optical skyrmion, anti-skyrmion, and 2nd-order skyrmion structures. The significant difference between the topological state transitions of these two cases originates from the transformation from the paraxial optical system to the nonparaxial optical system, and the approximate two-dimensional polarization structure to the three-dimensional polarization structure. The results provide new insights into the topological state transitions in topological structures, which promote applications in information processing, data storage, and free-space optical communications.

Nanoparticle Deep-Subwavelength Dynamics Empowered by Optical Meron-Antimeron Topology

Optical meron is a type of nonplanar topological texture mainly observed in surface plasmon polaritons and highly symmetric points of photonic crystals in the reciprocal space. Here, we report Poynting-vector merons formed at the real space of a photonic crystal for a Γ-point illumination. Optical merons can be utilized for subwavelength-resolution manipulation of nanoparticles, resembling a topological Hall effect on electrons via magnetic merons. In particular, staggered merons and antimerons impose strong radiation pressure on large gold nanoparticles (AuNPs), while focused hot spots in antimerons generate dominant optical gradient forces on small AuNPs. Synergistically, differently sized AuNPs in a still environment can be trapped or orbit in opposite directions, mimicking a coupled galaxy system. They can also be separated with a 10 nm precision when applying a flow velocity of >1 mm/s. Our study unravels a novel way to exploit topological textures for optical manipulation with deep-subwavelength precision and switchable topology in a lossless environment.

Regulating the electronic structure of metal-organic frameworks via ion-exchanged Ir dispersion for robust overall water splitting

A facile ion exchange strategy to fabricate CoIrx-BDC with atomically dispersed Ir is developed towards overall water splitting. The optimized CoIr3-BDC requires only 12 and 81 mV to deliver 10 and 100 mA cm-2 alkaline HER, respectively, and only 245 mV to reach 100 mA cm-2 alkaline OER.

Dynamic manipulation of graphene plasmonic skyrmions

With the characteristics of ultrasmall, ultrafast, and topological protection, optical skyrmions are great prospects for applications in high intensity data stroage, high resolution microscopic imaging, and polarization sensing. Flexible control over the topology of optical skyrmions is required for practical implementation/application. At present, the manipulation of optical skyrmions usually relies upon the change of spatial structure, which results in a limited-tuning range and a discontinuous control in the parameter space. Here, we propose continuous manipulation of the graphene plasmon skyrmions based on the electrotunable properties of graphene. By changing the Fermi energy of one pair of the standing waves or the phase of incident light, one can achieve topological state transformation of graphene plasmon skyrmions, which is evident by the change of skyrmion number from 1 to 0.5. The direct manipulation of the graphene plasmon skyrmions is demonstrated by simulation results based on the finite element method. Our work suggests a feasible way to flexibly control the topology of an optical skyrmionic field, which can be used for novel integrated photonic devices in the future.

2D Ferroionics: Conductive Switching Mechanisms and Transition Boundaries in Van der Waals Layered Material CuInP2 S6

The recently unfolded ferroionic phenomena in 2D van der Waals (vdW) copper-indium-thiophosphate (CuInP2 S6 or CIPS) have received widespread interest as they allow for dynamic control of conductive switching properties, which are appealing in the paradigm-shift computing. The intricate couplings between ferroelectric polarization and ionic conduction in 2D vdW CIPS facilitate the manipulation and dynamic control of conductive behaviors. However, the complex interplays and underlying mechanisms are not yet fully explored and understood. Here, by investigating polarization switching and ionic conduction in the temperature and applied electric field domains, it is discovered that the conducting mechanisms of CIPS can be divided into four distinctive states (or modes) with transitional boundaries, depending on the dynamics of Cu ions in the material. Further, it demonstrates that dynamically-tunable synaptic responsive behavior can be well implemented by governing the working-state transition. This research provides an in-depth, quantitative understanding of the complex phenomena of conductive switching in 2D vdW CIPS with coexisting ferroelectric order and ionic disorder. The developed insights in this work lay the ground for implementing high-performance, function-enriched devices for information processing, data storage, and neuromorphic computing based on the 2D ferroionic material systems.

Néel-type optical target skyrmions inherited from evanescent electromagnetic fields with rotational symmetry

Optical skyrmions have recently attracted growing interest due to their potential applications in deep-subwavelength imaging and nanometrology. While optical skyrmions have been successfully demonstrated using different field vectors, the study of their generation and control, as well as their general correlation with electromagnetic (EM) fields, is still in its infancy. Here, we theoretically propose that evanescent transverse-magnetic-polarized (TM-polarized) EM fields with rotational symmetry are actually Néel-type optical target skyrmions of the electric field vectors. Such optical target skyrmions are independent of the operation frequency and medium. Our proposal was verified by numerical simulations and real-space nano-imaging experiments performed on a graphene monolayer, where the target skyrmions could be as small as ∼100 nm in diameter. The results can therefore not only further our understanding of the formation mechanisms of EM topological textures, but also provide guidelines for the facile construction of EM skyrmions that may impact future information technologies.

Respiration-Responsive Colorful Room-Temperature Phosphorescent Materials and Assembly-Induced Phosphorescence Enhancement Strategies

It is still very challenging to obtain colorful and long-afterglow room-temperature phosphorescent (RTP) materials from pure organic polymers. Herein, it is found that chitosan (CS), a natural polymer, not only has its own RTP, but also reacts with different phosphorescent molecules to obtain a multicolor, long-afterglow RTP material. CS can emit RTP with a lifetime of 48 ms. In addition, CS is rich in amino groups, and grafting different phosphorescent molecules onto CS by an amidation reaction can modulate it to emit different colors of phosphorescence and obtain a series of colorful CS derivatives. The obtained polymer films also have ultra-long RTP due to the good film-forming ability. In addition, one of the CS derivatives selected with α-cyclodextrin is used to construct RTP materials with lifetimes of up to seconds. The host-guest interactions are used to suppress nonradiative relaxation and build crystalline domains, thus synergistically enhancing the RTP. Interestingly, the RTP properties of the CS derivative films are extremely sensitive to water and heat stimuli, because water broke the hydrogen bonds between adjacent CS molecules and thus altered the rigid environment in the material. Finally, they can be used as a stimuli-responsive ink and for monitoring environmental humidity.

Tuning magneto-electric coherent resonance with a deep-subwavelength localized spoof surface plasmonic structure

It has been recently shown that an ultrathin corrugated spiral metal strip can simultaneously support electric and magnetic localized spoof plasmonic modes at lower frequencies. In this Letter, we report a mirror quasi-symmetrical corrugated spiral metal disk which can support coherent resonance of an orthogonal electric dipole and a magnetic dipole to achieve azimuthally symmetric unidirectional scattering. By tuning the geometric dimensions, reconfigurable magneto-electric (ME) coherent resonance enhancement is realized. Excellent agreement between numerical simulations and experimental results verifies the tunable ME coherent resonance phenomenon. Our finding could anticipate future sensitive and versatile functional devices based on high-Q coherent resonance from the microwave to the terahertz bands.

Metastability of photonic spin meron lattices in the presence of perturbed spin-orbit coupling

Photonic skyrmions and merons are topological quasiparticles characterized by nontrivial electromagnetic textures, which have received increasing research attention recently, providing novel degree of freedom to manipulate light-matter interactions and exhibiting excellent potential in deep-subwavelength imaging and nanometrology. Here, the topological stability of photonic spin meron lattices, which indicates the invariance of skyrmion number and robustness of spin texture under a continuous deformation of the field configuration, is demonstrated by inducing a perturbation to break the C₄ symmetry in the presence spin-orbit coupling in an optical field. We revealed that amplitude perturbation would result in an amplitude-dependent shift of spin center, while phase perturbation leads to the deformation of domain walls, manifesting the metastability of photonic meron. Such spin topology is verified through the interference of plasmonic vortices with a broken rotational symmetry. The results provide new insights on optical topological quasiparticles, which may pave the way towards applications in topological photonics, optical information storage and transfer.

Recent Advances in Ultrathin Chiral Metasurfaces by Twisted Stacking

Artificial chiral nanostructures have been subjected to extensive research for their unique chiroptical activities. Planarized chiral films of ultrathin thicknesses are in particular demand for easy on-chip integration and improved energy efficiency as polarization-sensitive metadevices. Recently, controlled twisted stacking of two or more layers of nanomaterials, such as 2D van der Waals materials, ultrathin films, or traditional metasurfaces, at an angle has emerged as a general strategy to introduce optical chirality into achiral solid-state systems. This method endows new degrees of freedom, e.g., the interlayer twist angle, to flexibly engineer and tune the chiroptical responses without having to change the material or the design, thus greatly facilitating the development of multifunctional metamaterials. In this review, recent exciting progress in planar chiral metasurfaces are summarized and discussed from the viewpoints of building blocks, fabrication methods, as well as circular dichroism and modulation thereof in twisted stacked nanostructures. The review further highlights the ever-growing portfolio of applications of these chiral metasurfaces, including polarization conversion, information encryption, chiral sensing, and as an engineering platform for hybrid metadevices. Finally, forward-looking prospects are provided.

Disorder-Induced Topological State Transition in the Optical Skyrmion Family

Skyrmions endowed with topological protection have been extensively investigated in various platforms including magnetics, ferroelectrics, and liquid crystals, stimulating applications such as memories, logic devices, and neuromorphic computing. While the optical counterpart has been proposed and realized recently, the study of optical skyrmions is still in its infancy. Among the unexplored questions, the investigation of the topology induced robustness against disorder is of substantial importance on both fundamental and practical sides but remains elusive. In this Letter, we manage to generate optical skyrmions numerically in real space with different topological features at will, providing a unique platform to investigate the robustness of various optical skyrmions. A disorder-induced topological state transition is observed for the first time in a family of optical skyrmions composed of six classes with different skyrmion numbers. Intriguingly, the optical skyrmions produced from a vectorial hologram are exceptionally robust against scattering from a random medium, shedding light on topological photonic devices for the generation and manipulation of robust states for applications including imaging and communication.

Spontaneous generation and active manipulation of real-space optical vortices

Optical vortices are beams of light that carry orbital angular momentum¹, which represents an extra degree of freedom that can be generated and manipulated for photonic applications^2-8. Unlike vortices in other physical entities, the generation of optical vortices requires structural singularities^9-12, but this affects their quasiparticle nature and hampers the possibility of altering their dynamics or making them interacting^13-17. Here we report a platform that allows the spontaneous generation and active manipulation of an optical vortex-antivortex pair using an external field. An aluminium/silicon dioxide/nickel/silicon dioxide multilayer structure realizes a gradient-thickness optical cavity, where the magneto-optic effects of the nickel layer affect the transition between a trivial and a non-trivial topological phase. Rather than a structural singularity, the vortex-antivortex pairs present in the light reflected by our device are generated through mathematical singularities in the generalized parameter space of the top and bottom silicon dioxide layers, which can be mapped onto real space and exhibit polarization-dependent and topology-dependent dynamics driven by external magnetic fields. We expect that the field-induced engineering of optical vortices that we report will facilitate the study of topological photonic interactions and inspire further efforts to bestow quasiparticle-like properties to various topological photonic textures such as toroidal vortices, polarization and vortex knots, and optical skyrmions.

Recent advances in microresonators and supporting instrumentation for electron paramagnetic resonance spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy characterizes the magnetic properties of paramagnetic materials at the atomic and molecular levels. Resonators are an enabling technology of EPR spectroscopy. Microresonators, which are miniaturized versions of resonators, have advanced inductive-detection EPR spectroscopy of mass-limited samples. Here, we provide our perspective of the benefits and challenges associated with microresonator use for EPR spectroscopy. To begin, we classify the application space for microresonators and present the conceptual foundation for analysis of resonator sensitivity. We summarize previous work and provide insight into the design and fabrication of microresonators as well as detail the requirements and challenges that arise in incorporating microresonators into EPR spectrometer systems. Finally, we provide our perspective on current challenges and prospective fruitful directions.

Nanoscale Valley Modulation by Surface Plasmon Interference

Excitons in two-dimensional (2D) materials have attracted the attention of the community to develop improved photoelectronic devices. Previous reports are based on direct excitation where the out-of-plane illumination projects a uniform single-mode light spot. However, because of the optical diffraction limit, the minimal spot size is a few micrometers, inhibiting the precise manipulation and control of excitons at the nanoscale level. Herein, we introduced the in-plane coherent surface plasmonic interference (SPI) field to excite and modulate excitons remotely. Compared to the out-of-plane light, a uniform in-plane SPI suggests a more compact spatial volume and an abundance of mode selections for a single or an array of device modulation. Our results not only build up a fundamental platform for operating and encoding the exciton states at the nanoscale level but also provide a new avenue toward all-optical integrated valleytronic chips for future quantum computation and information applications.