Polarization Field Research Articles

Spin-Locked WS2 Vortex Emission via Photonic Crystal Bound States in the Continuum.

Owing to their strong exciton effects and valley polarization properties, monolayer transition-metal dichalcogenides (1L TMDs) have unfolded the prospects of spin-polarized light-emitting devices. However, the wavefront control of exciton emission, which is critical to generate structured optical fields, remains elusive. In this work, the experimental demonstration of spin-locked vortex emission from monolayer Tungsten Disulfide (1L WS2) integrated with Silicon Nitride (SiNx) PhC slabs is presented. The symmetry-protected bound states in the continuum (BIC) in the SiNx PhC slabs engender azimuthal polarization field distribution in the momentum space with a topological singularity in the center of the Brillouin zone, which imposes the resonantly enhanced WS2 exciton emission with a spin-correlated spiral phase front by taking advantage of the winding topologies of resonances with the assistance of geometric phase scheme. As a result, exciton emission from 1L WS2 exhibits helical wavefront and doughnut-shaped intensity beam profile in the momentum space with topological charges locked to the spins of light. This strategy on spin-dependent excitonic vortex emission may offer the unparalleled capability of valley-polarized structured light generation for 1L TMDs.

A road map to cosmological parameter analysis with third-order shear statistics

Context. Third-order lensing statistics contain a wealth of cosmological information that is not captured by second-order statistics. However, the computational effort it takes to estimate such statistics in forthcoming stage IV surveys is prohibitively expensive. Aims. We derive and validate an efficient estimation procedure for the three-point correlation function (3PCF) of polar fields such as weak lensing shear. We then use our approach to measure the shear 3PCF and the third-order aperture mass statistics on the KiDS-1000 survey. Methods We constructed an efficient estimator for third-order shear statistics that builds on the multipole decomposition of the 3PCF. We then validated our estimator on mock ellipticity catalogs obtained from N-body simulations. Finally, we applied our estimator to the KiDS-1000 data and presented a measurement of the third-order aperture statistics in a tomographic setup. Results. Our estimator provides a speedup of a factor of ∼100–1000 compared to the state-of-the-art estimation procedures. It is also able to provide accurate measurements for squeezed and folded triangle configurations without additional computational effort. We report a significant detection of tomographic third-order aperture mass statistics in the KiDS-1000 data (S/N = 6.69). Conclusions. Our estimator will make it computationally feasible to measure third-order shear statistics in forthcoming stage IV surveys. Furthermore, it can be used to construct empirical covariance matrices for such statistics.

Ferroelectric polarization synergism boosting CdS/PbTiO3 S-scheme heterostructures for efficiently bifunctional environmental applications

It is of great significance and challenges to construct physical field-enhanced photocatalysts for energy and environmental applications. Herein, an artificial-photosynthesized CdS/PbTiO3 S-scheme heterostructures with the enhancement of polarization electric field have been developed to promote the bifunctionally catalytic efficiencies for Cr(VI) photoreduction degradation of heavy metal pollution and Tetracycline (TC) photooxidation degradation of antibiotic. In our work, CdS nanoparticles are selectively grown on the positive polarization planes of PbTiO3 microplates to form the same direction for both the ferroelectric polarization field of PbTiO3 and the built-in electric field of S-scheme heterojunction. In this case, the stable heterostructures of PTO(00−1)/CdS(010) are obtained, and the greatly improved photocatalytic performances of redox degradation are achieved. The charge transfer mechanism and the synergetic effect between the spontaneous ferroelectric polarization and S-scheme heterojunction have been revealed by DFT calculations and experimental verifications. This interesting finding provides new insight into the design of efficient artificial-photosynthesized photocatalytic systems and we hope our work could serve as a valuable reference for our colleagues.

Enhancing Zn2+/H+ Joint Charge Storage in MnO2: Concurrently Tailoring Mn's Local Electron Density and O's p-Band Center.

Enhancing proton storage in the zinc-ion battery cathode material of MnO2 holds promise in promoting its electrochemical performance by mitigating the intense Coulombic interaction between divalent zinc ions and the host structure. However, challenges persist in addressing the structural instability caused by Jahn-Teller effects and accurately modulating H+ intercalation in MnO2. Herein, the doping of high-electronegativity Sb with fully occupied d-orbital in MnO2 is reported. The Sb doping strategy engenders the formation of Mn-O-Sb path in the structure with a strong dipole polarization field, which facilitates the delocalization of eg orbital electron in Mn and thus mitigates the Jahn-Teller effects. Simultaneously, adjusting the level of Sb doping in MnO2 leads to modulation of the p-band center of O, optimizing its interaction with hydrogen and thereby enhancing proton storage. Consequently, MnO2 doped with 6% Sb exhibits commendable performance in both rate capability and cycling endurance, delivering 113 mAh g-1 at 2 A g-1 after 2000 cycles. This investigation underscores the crucial role of electronic structural engineering in elevating the electrochemical performance of cathode materials for zinc-ion batteries.

Magnetically Driven Turbulence in the Inner Regions of Protoplanetary Disks

Given the important role turbulence plays in the settling and growth of dust grains in protoplanetary disks, it is crucial that we determine whether these disks are turbulent and to what extent. Protoplanetary disks are weakly ionized near the midplane, which has led to a paradigm in which largely laminar magnetic field structures prevail deeper in the disk, with angular momentum being transported via magnetically launched winds. Yet, there has been little exploration of the precise behavior of the gas within the bulk of the disk. We carry out 3D, local shearing box simulations that include all three low-ionization effects (ohmic diffusion, ambipolar diffusion, and the Hall effect) to probe the nature of magnetically driven gas dynamics 1–30 au from the central star. We find that gas turbulence can persist with a generous yet physically motivated ionization prescription (order unity Elsässer numbers). The gas velocity fluctuations range from 0.03 to 0.09 of the sound speed c s at the disk midplane to ∼c s near the disk surface, and are dependent on the initial magnetic field strength. However, the turbulent velocities do not appear to be strongly dependent on the field polarity, and thus appear to be insensitive to the Hall effect. The midplane turbulence has the potential to drive dust grains to collision velocities exceeding their fragmentation limit, and likely reduces the efficacy of particle clumping in the midplane, though it remains to be seen if this level of turbulence persists in disks with lower ionization levels.

First-principles study of the structure, electronic and optical properties of monolayer ZrX3 (X = S, Se, Te).

The structure, electronic and optical properties of single-layer transition metallic chalcogenides ZrX3 (X = S, Se, Te) have been studied by density functional theory. The electron energy dispersion curve shows that ZrX3 has semiconductor properties, in which the conduction band is mainly contributed by the correlated states of the Zr-d orbital, and the valence band is mainly contributed by the correlated states of the X-p orbital. It is found that b-axis and biaxial strain have great influence on the bandgap and the shift of density of states is also large. At the same time, the peak value of density of states increases greatly when biaxial strain is applied. It is of guiding significance for selecting suitable substrates to prepare two-dimensional ZrX3 materials to study their electronic properties. The calculation of optical constants confirms that ZrX3 has strong optical anisotropy. In the visible range, the light absorption efficiency of ZrX3 in the direction of electric field polarization [100] is higher than that in the direction of [010]. The reflectance spectral results show that ZrS3 and ZrSe3 in the [100] directions have the highest reflectance, and ZrTe3 in the [010] direction has the highest reflectance, even in the long electromagnetic radiation range (up to 10eV), which is of great significance for the construction of visible optical devices. All computations have been carried out based on density functional theory (DFT) as implemented in the CASTEP code. The pseudo-potential is adopted by the norm conserving, and the exchange correlation functional is adopted by the Perdew-Burke-Ernzerhof in local generalized gradient approximation (GGA).

Earth's ambipolar electrostatic field and its role in ion escape to space.

Cold plasma of ionospheric origin has recently been found to be a much larger contributor to the magnetosphere of Earth than expected1-3. Numerous competing mechanisms have been postulated to drive ion escape to space, including heating and acceleration by wave-particle interactions4 and a global electrostatic field between the ionosphere and space (called the ambipolar or polarization field)5,6. Observations of heated O+ ions in the magnetosphere are consistent with resonant wave-particle interactions7. By contrast, observations of cold supersonic H+ flowing out of the polar ionosphere8,9 (called the polar wind) suggest the presence of an electrostatic field. Here we report the existence of a +0.55 ± 0.09 V electric potential drop between 250 km and 768 km from a planetary electrostatic field (E∥⊕ = 1.09 ± 0.17 μV m-1) generated exclusively by the outward pressure of ionospheric electrons. We experimentally demonstrate that the ambipolar field of Earth controls the structure of the polar ionosphere, boosting the scale height by 271%. We infer thatthis increases the supply of cold O+ ions to the magnetosphere by more than 3,800%, in which other mechanisms such as wave-particle interactions can heat and further accelerate them to escape velocity. The electrostatic field of Earth is strong enough by itself to drive the polar wind9,10 and is probably the origin of the cold H+ ion population1 that dominates much of the magnetosphere2,3.

Ferroelectric nematic fluids as spontaneous polarization field for enhanced orientational-dependent second-harmonic generation

ABSTRACT Second-order nonlinear optical effects have piqued researchers’ interest in fundamental physics and practical perspectives. The ferroelectric nematic liquid crystals (NF LCs) have recently drawn attention to LC nonlinear optical applications due to their relatively high second-harmonic generation output. Further improving the nonlinear optical properties to get closer to the performance of inorganic nonlinear optical materials is challenging. Here, we take a blending strategy to enhance the nonlinear optical response of a prototype NF LC, DIO. We mixed an organic nonlinear optical crystalline material, 3,5,5-trimethyl (cyclohex-2-enylidene) malononitrile (TCM), with DIO and investigated the effects of TCM doping at various concentrations. We quantitatively determined the second-harmonic generation and spontaneous polarization as functions of temperature and concentration. We found that, compared with the pure DIO, the second-harmonic generation performance increased by about 130% at maximum, 93% in maximum for the nonlinear optical coefficient, and 10% in maximum for spontaneous polarization.

Global Effect of New Active Regions on Coronal Holes and Their Wind Streams

Solar wind prediction algorithms and simulations of coronal events often employ photospheric field maps that are assembled over a 27 day solar rotation. This has stimulated efforts to update and better synchronize the maps by applying flux transport and including observations of the back side of the Sun. Here, using potential-field source-surface extrapolations, we address the question of how the emergence of a large active region (AR) on the Sun’s farside affects the coronal field and configuration of coronal holes on the Earth-facing side. We find that, if the new AR is located ∼135°–180° in longitude from Earth, the effect on the coronal field and solar wind near the central meridian will be almost negligible. This is because, when sunspot activity is relatively low, the outermost AR loops will become connected to the nearby polar fields; when sunspot activity is high, the newly emerged flux will connect to neighboring ARs. However, large ARs that emerge near the solar limb may sometimes have a significant effect on the field near the central meridian. In particular, a coronal hole having opposite polarity to that of the nearest sector of the AR may partially close down, resulting in slower wind; conversely, if the coronal hole has the same polarity as the facing AR sector, it will tend to increase in areal size, resulting in faster wind. In most cases, the main effect of a new AR will be to redistribute open flux between itself and neighboring coronal holes (including the polar holes) through interchange reconnection.

Reflective multi-layer metasurface based on half-wave plate structure for polarization control in the visible-near-infrared region

The precise control of the polarization of the electromagnetic field in the optical range is studied. A numerical simulation was performed, which corresponds to the optical devices operating in the 650–800 nm range and does not present any obstacles for fabrication. According to this, the three-layer system based on metasurfaces was developed, which operates as a half-wave plate consisting of a metal-dielectric-metal structure and takes very small dimensions, more than 3 times smaller than the observed wavelength. This half-wave plate is reflective and exhibits almost ideal behavior with a spectral width of about 10 nm within 735–745 nm. The losses are negligible, and the amplitude ratio of the directly reflected components in almost the entire studied spectrum exceeds 90%. With a spectrum of about 100 nm within 650–800 nm, it is 99%. Also, the system has an advantage characteristic of metasurfaces: regardless of the angle of the incident wave with the normal, it shows high efficiency, and even when the incident wave is below 45°, the polarization conversion ratio (PCR) remains greater than 80%. The system has optimal geometric dimensions, which works especially well, but even if the dimensions change (due to fabrication defects), its effectiveness does not weaken. The proposed system can become a very promising optical device and be used to control the state of electromagnetic waves in the optical range.

Enhanced Energy Storage Properties of Highly Polarized BMT-Based Thin Films through the Multiscale Structure Synergistic Regulation Strategy.

For solving the trade-off relationship of the polarization and breakdown electric field, ferroelectric films with high polarization are playing a critical role in energy storage capacitor applications, especially at moderate/low electric fields. In this work, we propose a multiscale structure (including defect, domain, and grain structures) synergetic optimization strategy to optimize the polarization behavior and energy storage performances of BiMg0.5Ti0.5O3 (BMT) ferroelectric films by introducing Sr0.7La0.2TiO3 (SLT) without compromising the breakdown strength. At a moderate electric field of 2917 kV/cm, a high discharge density of 72.2 J/cm3 has been achieved in 0.9BMT-0.1SLT films, together with good frequency, thermal, and cycle stabilities for energy storage. Importantly, the phase difference Δφ is utilized to quantitatively evaluate the polarization switching mobility of the ferroelectric domain/PNRs at an external electric field stimulation. This research demonstrates that a multiscale structure optimization strategy could effectively regulate the energy storage performance, and ecofriendly BMT-based materials are promising candidates for next-generation energy storage capacitors, especially at moderate/low electric fields.

Phase-field simulations of ferro-electro-elasticity in model polycrystals with implications for phenomenological descriptions of bulk perovskite ceramics

We investigate the role of polycrystalline disorder on the effective ferro-electro-elastic behavior of perovskite ferroelectric ceramics under electro-mechanical loading. Assuming random initial grain orientations, we use high-resolution phase-field simulations and periodic homogenization of two-dimensional model polycrystals to study the evolution of the domain microstructure within and across grains as well as the resulting effective, macroscopic polarization and strain fields under loading. The number of randomly-oriented grains in simulations, at fixed grain size and fixed numerical resolution per grain, is used to control the polycrystalline disorder. Results indicate that, when the polycrystalline samples are sufficiently disordered (i.e., when sufficiently many randomly-oriented grains are considered), their effective electromechanical response under uniaxial compression is stable, and the concomitant polarization and deformation are always aligned with the mechanical load. Thus, the present study supports the viewpoint that polycrystalline disorder in bulk perovskite ceramics stabilizes the overall ferro-electro-elastic response despite the underlying nonconvex polarization energy landscape.

Dipole polarization-driven spatial charge separation in defective zinc cadmium sulfoselenide for boosting photocatalytic hydrogen evolution

The industrial interest of ZnCdS as the photocatalytic media for hydrogen evolution reaction (HER) is severely hindered by its sluggish interfacial charge transfer, limited active sites, and serious photocorrosions. Herein, to catalyze more efficient and robust HER, a series of Se-doped ZnCdS with sulfur vacancies (denoted as Se/VS-ZnCdS) are ingeniously designed and facilely synthesized. Experimental and theoretical studies reveal that by inducing dipole polarization through defect engineering synergistic elemental doping, spontaneous polarization field is generated in the bulk phase of ZnCdS, which together with elevated Fermi level renders the Se/VS-ZnCdS with desirable spatial charge separation and transfer. Thus, the optimal 0.6 %Se/VS-ZnCdS exhibits the outstanding performance of 85.3 mmol·gcat−1·h−1 and excellent stability up to 24 h. This work highlights the high efficiency of dipole polarization realized by vacancy synergistic atomic doping in optimizing HER kinetics, and provides a new pathway to develop robust photocatalysts based on metal sulfoselenide for water-splitting reactions.

Reduction of green-gap effect for light-emitting diodes using InGaN-ZnGeN2-InGaN/GaN type-II MQW

In this work, the design of two multiple-quantum-wells (MQWs) green LEDs are investigated − (i) LED A with standard InGaN/GaN type I band alignment quantum wells (QWs), and (ii) LED B with InGaN-ZnGeN2-InGaN/GaN type II band alignment QWs. Using numerical program we obtain energy band diagram, carrier concentration, electric field, electroluminescence spectra and radiative-recombination-rate (RRR). Owing to presence of strong polarization field and compositional inhomogeneity in InGaN/GaN heterostructure, it is hard to obtain the high efficiency in wavelength of 500–600 nm, termed as ‘green-gap’ effect. Introduction of InGaN-ZnGeN2-InGaN QWs reduces the piezoelectric polarization field and enhances overlapping between electron-hole wave functions thereby increasing RRR. Moreover, holes are distributed uniformly in all QWs in the active region of LED that leads to improved emission efficiency. The proposed device, LED B exhibits 710 % more output optical power and less wall-plug efficiency droop is only 3.1 % in contrast to 82.4 % in LED A.

Transmembrane Graphene as an Electron Tunnel to Regulate the Intracellular Redox State.

Cellular redox homeostasis is essential for maintaining cellular activities, such as DNA synthesis and gene expression. Inspired by this, new therapeutic interventions have been rapidly developed to modulate the intracellular redox state using artificial transmembrane electron transport. However, current approaches that rely on external electric field polarization can disrupt cellular functions, limiting their in vivo application. Therefore, it is crucial to develop novel electric-field-free modulation methods. In this work, we for the first time found that graphene could spontaneously insert into living cell membranes and serve as an electron tunnel to regulate intracellular reactive oxygen species and NADH based on the spontaneous bipolar electrochemical reaction mechanism. This work provides a wireless and electric-field-free approach to regulating cellular redox states directly and offers possibilities for biological applications such as cell process intervention and treatment for neurodegenerative diseases.

Uncovering quantum characteristics of incipient evolutions at the photosynthetic oxygen evolving complex

Water oxidation of photosynthesis at the oxygen evolving complex (OEC) is driven by the polarization field induced by the photoelectric hole. By highlighting the role of the polarization field in reshaping the spin and orbit potentials, we reveal in this work the characteristics and underlying mechanism in the relatively simpler OEC evolutions within the states S0–S2 prior to the water oxidation. The characteristic shifts of the density of states (DOS) of the electron donor Mn atom are observed in the vicinity of the Fermi surface to occur with the spin flips of Mn atoms and the change in the Mn oxidation states during the electron transfer. Notably, the spin flips of Mn atoms point to the resulting spin configuration of the next states. It is found that the electron transfer tends to stabilize the catalyst OEC itself, whereas the proton transfer pushes the evolution forward by preparing a new electron donor, demonstrating the proton-coupled electron transfer. Meanwhile, it shows that the Mn–O bonds around the candidate Mn atom of the electron donor undergo characteristic changes in the bond lengths during the electron transfer. These concomitant phenomena uncovered in first-principle calculations characterize the essential equilibrium of the OEC between the state evolution and stability that forms the groundwork of the dynamic OEC cycles. In particular, the characteristic undulation of the DOS around the Fermi level occurring at the proton-coupled electron transfer can be used to reveal crucial processes in a wide range of realistic systems.

Controlling the polarization through opposite orthogonal transformation with coupling-optimized composite metasurface

The flexible manipulation of incident polarized waves enhances design freedom for integrated and miniaturized THz devices. This work proposes a method of orthogonal decomposition and transformation to manipulate the polarization of incident fields. It enables symmetric mapping with respect to the S2 axis (x = y) on the Poincaré sphere for any polarized waves. Consequently, arbitrary deflection can be achieved by adjusting the angle between the incident wave and the device. Additionally, the spin will be reversed for circularly and elliptically polarized waves. A specific metasurface is designed to implement this proposal, incorporating a precisely tailored coupling structure to optimize the interaction between cells, which is crucial for maintaining transmittance and bandwidth. All designs are thoroughly validated through numerical simulations. This adaptability and flexibility make it suitable for various applications, including waveplates, polarization convertors and detectors, antennas and radars, etc.

Dynamic flexoelectric instabilities in nematic liquid crystals.

Electrohydrodynamic phenomena in liquid crystals constitute an old but still very active research area. The reason is that these phenomena play the key role in various applications of liquid crystals and due to the general interest of the physical community in out-of-equilibrium systems. Nematic liquid crystals (NLCs) are ideally representative for such investigations. Our article aims to study theoretically the linear NLCs dynamics. We include into consideration orientation elastic energy, hydrodynamic motion, external alternating electric field, electric conductivity, and flexoelectric polarization. We analyze the linear stability of the NLC film, determining dynamics of perturbations with respect to the homogeneous initial state of the NLC. For the purpose we compute eigenvalues of the evolution matrix for a period of the external alternating electric field. These eigenvalues determine the amplification factors for the modes during the period. The instability occurs when the principal eigenvalue of the evolution matrix becomes unity by its absolute value. The condition determines the threshold (critical field) for the instability of the uniform state. It turns out that one might expect various types of the instability, only partially known and investigated in the literature. Particularly, we find that the flexoelectric instability may lead to two-dimensionally space-modulated patterns exhibiting time oscillations. This type of the structures was somehow overlooked in the previous works. We formulate conditions needed for the scenario to be realized. We hope that the results of our work will open the door to a broad range of further studies. Of especial importance would be a comprehensive understanding of the role of various material parameters and nonlinear effects which is a key step for the rational design of NLCs exhibiting the predicted in this publication multidimensional oscillating in time patterns.

Customizing Pore Structure and Lithiophilic Sites Dual-Gradient Free-Standing 3D Lithium-Based Anode to Enable Excellent Lithium Metal Batteries.

Developing 3D hosts is one of the most promising strategies for putting forward the practical application of lithium(Li)-based anodes. However, the concentration polarization and uniform electric field of the traditional 3D hosts result in undesirable "top growth" of Li, reduced space utilization, and obnoxious dendrites. Herein, a novel dual-gradient 3D host (GDPL-3DH) simultaneously possessing gradient-distributed pore structure and lithiophilic sites is constructed by an electrospinning route. Under the synergistic effect of the gradient-distributed pore and lithiophilic sites, the GDPL-3DH exhibits the gradient-increased electrical conductivity from top to bottom. Also, Li is preferentially and uniformly deposited at the bottom of the GDPL-3DH with a typical "bottom-top" mode confirmed by the optical and SEM images, without Li dendrites. Consequently, an ultra-long lifespan of 5250h of a symmetrical cell at 2mA cm-2 with a fixed capacity of 2 mAh cm-2 is achieved. Also, the full cells based on the LiFePO4, S/C, and LiNi0.8Co0.1Mn0.1O2 cathodes all exhibit excellent performances. Specifically, the LiFePO4-based cell maintains a high capacity of 136.8 mAh g-1 after 700 cycles at 1C (1C = 170mA g-1) with 94.7% capacity retention. The novel dual-gradient strategy broadens the perspective of regulating the mechanism of lithium deposition.

Emergent chirality in active solid rotation of pancreas spheres

Collective cell dynamics play a crucial role in many developmental and physiological contexts. While two-dimensional (2D) cell migration has been widely studied, how three-dimensional (3D) geometry and topology interplay with collective cell behavior to determine dynamics and functions remains an open question. In this work, we elucidate the biophysical mechanism underlying rotation in spherical tissues, a phenomenon widely reported both and . Using murine pancreas-derived organoids as a model system, we find that epithelial spheres exhibit persistent rotation, rotational axis drift, and rotation arrest. Using a 3D vertex model, we demonstrate how the combined action of traction force and polarity alignment can account for these distinct rotational dynamics near a solid to flow transition. Furthermore, our analysis shows that the spherical tissue rotates as an active solid occasionally switching to a flowing state and exhibits spontaneous chiral symmetry breaking. Using a continuum model, we demonstrate how the topological defects in the polarity field underlie this symmetry breaking process, which is revealed by asymmetries in the cell elongation pattern. For cell elongation to reveal the chiral asymmetry, shear flow is required in addition to the solid body rotation. Altogether, our work reveals a robust chiral symmetry breaking mechanism with potential implications for left-right symmetry breaking processes in morphogenetic events. Published by the American Physical Society 2024