Polarization Field Research Articles

Complete classification and additional saddle-point solutions for high-order above-threshold ionization induced by a strong laser field

Ionization of atoms by a strong laser field can be described using the improved strong-field approximation. The corresponding transition amplitude of high-order above-threshold ionization is presented in the form of a two-dimensional integral over the electron ionization time t0 and the rescattering time t. This integral can be solved using the saddle-point (SP) method and the resulting T-matrix element is expressed as a sum (over the SP times t0 and t) of the partial transition amplitudes. We address the problem of finding the solutions of the system of SP equations for the times t0 and t. For a bichromatic linearly polarized laser field with the frequencies rω and sω (r and s are integers, s>r, and ω is the fundamental frequency) we found that there are 8s2 SP solutions per optical cycle. For one half of them the velocity of the electron emitted in the laser field polarization direction changes the sign at the rescattering time (we call such solutions backward-scattering solutions), while for the other half this velocity remains unchanged (these solutions we call forward-scattering SP solutions). For very short (or even negative) electron travel time we call these solutions backward-like and forward-like scattering SP solutions. For these solutions the imaginary parts of the times t0 and t become large so that the concept of real electron trajectories becomes questionable. Having such a classification, we found additional SP solutions even for the simplest case of a monochromatic linearly polarized laser field. For a bichromatic linearly polarized laser field with s=2 and equal component intensities we presented a detailed analysis of all 32 solutions per optical cycle, showing how the SP times t0 and t and the corresponding differential ionization rates depend on the photoelectron energy. We have also analyzed the case where the intensity of the second component decreases while the sum of the component intensities remains fixed. Published by the American Physical Society 2025

Robust Coupling Between Piezoelectric Field and Interfacial Polarization in Layered Bismuth-Based Heterostructure for High-performance Piezocatalytic Water Splitting.

The creation of heterostructures with inherent interface polarization has been proven effective in enhancing piezocatalytic activity; however, developing efficient heterostructure piezocatalysts remains challenging, and the underlying mechanisms are not well understood. In this work, a stable Bi2WO6/BiOBr heterostructure with strong chemical binding is successfully constructed by exchanging double Br- with WO4 2- in hydrothermal reaction. The heterostructure demonstrates exceptional piezocatalytic hydrogen evolution reaction (HER) efficiencies of 0.75mmol g⁻¹ h⁻¹ in water and 2.28mmol g⁻¹ h⁻¹ in methanol solution, respectively, outperforming the majority of recently reported bismuth-based piezocatalysts. During piezocatalytic operations, a robust coupling between the stress-induced piezoelectric field and the inherent interfacial polarization is pivotal. This coupling results in a large intrinsic dipole moment, excellent piezoelectricity, and improved carrier separation and transfer. Additionally, the polar surface of heterostructure facilitates decreased Gibbs free energy, increased surface potential, and reduced charge transfer resistance, all of which contribute to the high-activity surface piezocatalytic reaction. This study introduces a simple and universal method for in situ construction of layered bismuth-based heterostructures with high piezocatalytic performance and offers valuable insights into the role of polarization coupling in piezocatalysis.

Stochastic Stokes origami: folds, cusps and skyrmionic facets in random polarisation fields

Abstract We consider the jacobian of a random transverse polarisation field, from the transverse plane to the Poincar\'e sphere, as a Skyrme density partially covering the sphere. Connected domains of the plane where the jacobian has the same sign—patches—map to facets subtending some general solid angle on the Poincar\'e sphere. As a generic continuous mapping between surfaces, we interpret the polarisation pattern on the sphere in terms of fold lines (corresponding to the crease lines between neighbouring patches) and cusp points (where fold lines meet). We perform a basic statistical analysis of the properties of the patches and facets, including a brief discussion of the polarisation analogue to superoscillation in scalar speckle patterns and the percolation properties of the jacobian domains. Connections with abstract origami manifolds are briefly considered. This analysis combines previous studies of structured skyrmionic polarisation patterns with random polarisation patterns, suggesting a particle-like interpretation of random patches as polarisation skyrmionic anyons.

Enhanced Interfacial Electric Field of an S−Scheme Heterojunction by an Ultrasonication‐Triggered Piezoelectric Effect for Sonocatalytic Therapy of Bacterial Infections

Sonodynamic therapy indicates advantages in combating antibiotics‐resistant bacteria and deep tissue infections, but challenges remain in the less efficient charge transfer and reactive oxygen species (ROS) generation of sonosensitizers. Herein, an effective bactericidal strategy is developed through enhancing the interfacial electric field (IEF) of S‐scheme heterojunctions by an ultrasonication‐triggered piezoelectric effect. Hollow barium titanate (hBT) nanoparticles (NPs) were prepared through template etching, followed by in‐situ assembly of tetrakis (4‐carboxyphenyl)porphyrin (TCPP) with Zn2+ to obtain hBT@ZnTCPP. Both experimental and theoretical evidences support the notion that an IEF is generared from ZnTCPP to hBT. Compared to metalloporphyrins with Fe3+, Mn3+, Cu2+ and Ni2+, the stronger reduction of ZnTCPP induced by elevation of the orbital energy level of porphyrins after Zn2+ coordination leads to formation of S‐scheme heterojunctions. The ultrasonication‐activated polarization field enhances IEF and boosts energy band bending of hBT@ZnTCPP to promote electron‐hole separations and ROS generations. Planktonic methicillin‐resistant Staphylococcus aureus and their derived biofilms are completely destroyed within 5 min under ultrasonication through up‐regulating genes of glucose catabolism and ion transportation and down‐regulating genes of ribosomal synthesis and transmembrane transporter. Thus, this study demonstrates molecular‐level modulation of energy levels for S‐scheme heterojunction formation to achieve efficient sonocatalytic therapy of bacterial infections.

Enhanced Interfacial Electric Field of an S-Scheme Heterojunction by an Ultrasonication-Triggered Piezoelectric Effect for Sonocatalytic Therapy of Bacterial Infections.

Sonodynamic therapy indicates advantages in combating antibiotics-resistant bacteria and deep tissue infections, but challenges remain in the less efficient charge transfer and reactive oxygen species (ROS) generation of sonosensitizers. Herein, an effective bactericidal strategy is developed through enhancing the interfacial electric field (IEF) of S-scheme heterojunctions by an ultrasonication-triggered piezoelectric effect. Hollow barium titanate (hBT) nanoparticles (NPs) were prepared through template etching, followed by in-situ assembly of tetrakis (4-carboxyphenyl)porphyrin (TCPP) with Zn2+ to obtain hBT@ZnTCPP. Both experimental and theoretical evidences support the notion that an IEF is generared from ZnTCPP to hBT. Compared to metalloporphyrins with Fe3+, Mn3+, Cu2+ and Ni2+, the stronger reduction of ZnTCPP induced by elevation of the orbital energy level of porphyrins after Zn2+ coordination leads to formation of S-scheme heterojunctions. The ultrasonication-activated polarization field enhances IEF and boosts energy band bending of hBT@ZnTCPP to promote electron-hole separations and ROS generations. Planktonic methicillin-resistant Staphylococcus aureus and their derived biofilms are completely destroyed within 5min under ultrasonication through up-regulating genes of glucose catabolism and ion transportation and down-regulating genes of ribosomal synthesis and transmembrane transporter. Thus, this study demonstrates molecular-level modulation of energy levels for S-scheme heterojunction formation to achieve efficient sonocatalytic therapy of bacterial infections.

Doppler velocity of m=1 high-latitude inertial mode over the last five sunspot cycles

A variety of solar global modes of oscillation in the inertial frequency range have been identified in maps of horizontal flows derived from GONG and HMI data. Among these, the high-latitude mode with azimuthal order m=1 (HL) has the largest amplitude and plays a role in shaping the Sun's differential rotation profile. We aim to study the evolution of the HL mode parameters, utilizing Dopplergrams from the Mount Wilson Observatory (MWO), GONG, and HMI, covering together five solar cycles since 1967. We calculated the averages of line-of-sight Doppler signals over longitude, weighted by the sine of longitude with respect to the central meridian, as a proxy for zonal velocity at the surface. We measured the mode's power and frequency from these zonal velocities at high latitudes in sliding time windows of three years. The HL mode is easily observed in the maps of zonal velocity at latitudes above 50 degrees, especially during solar minima. The mode parameters measured from the three independent data sets are consistent during their overlapping periods and agree with previous findings using HMI ring-diagram analysis. We find that the amplitude of the mode undergoes very large variations, taking maximum values at the start of solar cycles 21, 22, and 25, and during the rising phases of cycles 23 and 24. The mode amplitude is anticorrelated with the sunspot number (textrm corr =-0.50) but not correlated with the polar field strength. Over the period 1983--2022 the mode amplitude is strongly anticorrelated with the rotation rate at latitude $60^∘$ (textrm corr =-0.82), that is, with the rotation rate near the mode's critical latitude. The mode frequency variations are small and display no clear solar cycle periodicity above the noise level (∼ ± 3 nHz). Since about 1990, the mode frequency follows an overall decrease of ∼ 0.25 nHz/year, consistent with the long-term decrease of the angular velocity at $60^∘$ latitude. We have shown that the amplitude and frequency of the HL mode can be measured over the last five solar cycles, together with the line-of-sight projection of the velocity eigenfunction. We expect that these very long time series of the mode properties will be key to understand the dynamical interactions between the high-latitude modes, differential rotation, and (possibly) magnetic activity.

Interaction Between Strain and Phase Formation in HfxZr1-xO2 Thin Films.

HfxZr1-xO2 thin films have excellent complementary metal-oxide semiconductor compatibility and scalability compared to other ferroelectric materials. This makes them a promising candidate for non-volatile memory applications. However, the polymorphism of the materials presents a challenge in stabilizing the ferroelectric properties. Since the wake-up free non-volatile memory applications require the presence of ferroelectric properties in the pristine state of the films without additional electric field cycling, it is necessary to understand how to promote the ferroelectric orthorhombic phase formation. In this work, the interaction between in-plane tensile strain and phase formation of atomic layer deposition grown HfxZr1-xO2 thin films with different thicknesses and different compositions is demonstrated. By combining the biaxial in-plane tensile strain with the electric switching field and remanent polarization, it is observed that the best ferroelectric properties correlated with an in-plane tensile strain range of 0.4-0.6%. Moreover, the observed correlation between strain and phase formation indicates that strain exerts an influence on phase formation in the pristine state, and that phase formation, in turn, affects strain during electrical field cycling. This work is expected to be helpful to improve the ferroelectric properties in HfxZr1-xO2 films, which can be processed for different memory devices with specialized requirements.

Polarized electric field induced by piezoelectric effect of ozone micro-nano bubbles/spontaneously polarized ceramic to boost ozonolysis for efficient fruit sterilization.

Ozone (O3) treatment is an environmentally friendly fruit sterilization strategy. However, the low O3 utilization rate and long-term oxidation lead to O3 waste and fruit damage, respectively. Herein, a sterilization system based on the synergy of O3 micro-nano bubbles (OMNB) and spontaneously polarized ceramic (SPC) was developed to piezoelectrically catalyze ozonolysis for efficient fruit sterilization. OMNB/SPC showed excellent sterilizing activity with 7 lg CFU/mL of E. coli and S. aureus inactivation within 20min, together with significantly improved fruit quality in Kyoho grapes preservation. The excellent sterilizing performance of OMNB/SPC is attributed to that the piezoelectric SPC (d33=103.4pm/V) formed a strong polarized electric field and rich reactive oxygen species (ROS) under OMNB collapse resulting in O3 absorption/decomposition. The electric field and rich ROS caused membranes in-situ electroporation and irreversible inactivation to the microorganisms on fruits successively. This system is important for more efficient long-term preservation of fruits.

High-Performance Flexible Microwave Absorption Films with Dynamic Adjustable Macrostructures and Alterable Electromagnetic Field Polarizations.

Electromagnetic wave absorption materials that can be utilized for freewill adhering or peeling from the target substrate remain a challenge to be solved. Compared to powder-based slurry and coatings, microwave absorption films possess clear advantages for their good flexibility and machinability. However, the matching thickness and effective bandwidth of 2D microwave absorption films cannot satisfy the current application requirements. As a result, it is necessary to complete a rational structural design based on flat films. In view of the fact that common film-forming methods based on blocks or hard bases cannot be changed or replaced easily once the structural construction is done, here solvent evaporation molding combined with phase change material filling was proposed for the first time to accomplish continuous structural transformation for flexible films. Unlike the original reflection loss (RL) peaks of flat films at around 17.0 GHz, a new absorption peak near 12.25 GHz was generated thanks to the design of coherent structures, resulting in the peaks' boundary merging and effective bandwidth extension. Specifically, 4.56 GHz of absorption bandwidth (RL < -5 dB) at 1.0 mm and 4.27 GHz (RL < -10 dB) of absorption bandwidth at 2.3 mm could be obtained by arch testing under electrical field polarization. Importantly, correlations between EM field polarizations and coherent structures as well as the rules of the absorption peak generation and frequency shift related to the structural variation have all been figured out. The presented laws of EM pattern evolutions for structural films in this work lay the foundation for the applications of high-efficiency microwave absorption materials in complex surfaces and switchable scenes.

H-AMR FORGE’d in FIRE. I. Magnetic State Transitions, Jet Launching, and Radiative Emission in Super-Eddington, Highly Magnetized Quasar Disks Formed from Cosmological Initial Conditions

Abstract Quasars are powered by supermassive black hole (SMBH) accretion disks, yet standard thin disk models are inconsistent with many observations. Recently, P. F. Hopkins et al. simulated the formation of a quasar disk feeding an SMBH of mass M = 1.3 × 107 M ⊙ in a galaxy. The disk had surprisingly strong toroidal magnetic fields that supported it vertically from gravity and powered rapid accretion. What feedback can such a system produce? To answer this, we must follow the gas to the event horizon. For this, we interpolated the quasar into the general-relativistic radiation magnetohydrodynamics code H-AMR and performed 3D simulations with BH spins a = 0 and a = 0.9375. This remapping generates magnetic monopoles, which we erase using a novel divergence cleaning approach. Despite the toroidal magnetic field's dominance at large radii, vertical magnetic flux builds up near the event horizon, leading to a magnetic state transition within the inner 200 gravitational radii of the disk. This powers strong winds and, for spinning BHs, relativistic jets that can spin down the BH within 5−10 Myr. Sometimes, vertical magnetic fields of opposite polarity reach the BH, causing a polarity inversion event that briefly destroys the jets and, possibly, the X-ray corona. These strong fields power accretion at rates 5× the Eddington limit, which can double the BH mass in 5–10 Myr. When a = 0.9375 (a = 0), the energy in mechanical outflows and radiation equals about 60% (10%) and 100% (3%) of the accreted rest mass energy, respectively. Much of the light escapes in cool, ≳1300 au photospheres, consistent with quasar microlensing and spectral energy distributions.

Epitaxial growth of transition metal nitrides by reactive sputtering

Implementing transition metal nitride (TM-nitride) layers by epitaxy into group-III nitride semiconductor layer structures may solve substantial persisting problems for electronic and optoelectronic device configurations and subsequently enable new device classes in the favorable nitride semiconductor family. As a prominent example, the integration of the group-III-transition metal nitride AlScN enabled an improved performance of GaN based transistor structures due to stronger polarization fields as has been recently demonstrated. For other transition metal nitrides (TMNs) and their alloys with group-III nitrides a range of other interesting properties is expected to enable novel devices and applications. We investigated the compatibility of TM-nitride layers with the growth of GaN-based structures on silicon substrates. As we show TiN layers are compatible and particularly suited as highly conducting, metallic-like buffer layer enabling true vertical conduction without elaborate backside processing. Also, we demonstrate epitaxial growth of alloys based on ScN and AlN as well as of HfN layers on Si(111) substrates by reactive sputtering using high purity gases and targets. Particularly, we analyzed the crystal structure and the quality of Sc-rich AlxSc1-xN. For HfN layers, we find a unique impact on the growth polarity of MOVPE-grown GaN layers on Si(111) which changes to N-polar growth. This represents a simple and technologically scalable approach for N-polar GaN-based layers on Si substrates.

Influence of an external electromagnetic field on quantum entanglement and coherence in a two-qubit graphene system

Abstract Graphene, with its two-dimensional carbon structure, exhibits unique quantum properties that are crucial for quantum computing. In this paper, we investigate the influence of an external electromagnetic field on quantum coherence and entanglement between two qubits in graphene lattices. Our findings show that an electromagnetic field with high field strength ($\xi_{0} \sim 50$ meV$^2$) and low frequency ($\omega =0.117 \, \mathrm{eV}$) significantly enhances quantum entanglement and coherence, even at elevated temperatures ($T \sim 20$ meV). By adjusting the frequency and the field strength, these quantum effects can be preserved long enough at high temperatures. Furthermore, circular polarization of the electromagnetic field is found to be more effective than linear and elliptical polarizations in optimizing these effects. These results highlight the critical role of electromagnetic fields in enhancing quantum properties, potentially paving the way for advancements in quantum computing and related technologies.

Inner-heliospheric Signatures of Steadily Declining Solar Magnetic Fields and Their Possible Implications

Abstract We examined solar photospheric magnetic fields for the solar cycles 21–25, covering the period 1975–2024. The unsigned photospheric magnetic fields at low latitudes (0°–45°), known as solar toroidal fields, showed a solar cycle variation with the total field strength being stronger during the maximum of cycle 25 than the maximum of cycle 24. However, the unsigned field strength of photospheric magnetic fields at high latitudes (45°–78°), known as solar polar fields, has shown a significant steady decline since around the mid-1990s. The unsigned field strength of solar polar fields, after an increase during 2015–2020, has declined again until 2024, continuing the declining trend for a long 30 yr. Also, we examined the solar wind microturbulence levels in the inner heliosphere (0.2–0.8 au), using interplanetary scintillation observations at 327 MHz, covering the period 1983–2022, that steadily declined since the mid-1990s and continued until 2022, synchronously with the solar polar fields. We found that the floor level in both solar toroidal fields and solar wind magnetic fields was reduced during the minimum of cycle 23 and recovered back during the minimum of cycle 24. In addition, a hemispherically asymmetric solar polar reversal was evident in the signed (axial) solar polar fields during cycles 21–25, with the reversal in cycle 25 for the northern hemisphere already completed but the same for the southern hemisphere yet to be completed. We discuss the implications of the long declining trend and other anomalies in solar cycle activity.

Enhancement of Ferroelectric Properties of Ni-Substituted Pb2Fe2O5 Thin Films Synthesized by Reactive Magnetron Sputtering Deposition

Lead ferrite Pb2Fe2O5 (PFO) is a potential multiferroic material due its exhibition of ferroelectric and ferromagnetic properties. The effects of the substitution with nickel and synthesis temperature on the structural, morphological, and ferroelectric properties of lead ferrite thin films were investigated through the use of reactive magnetron sputtering deposition. Nickel loading concentrations were systematically varied (3%, 5%, and 10% by wt.%). X-ray diffraction analysis confirmed the formation of Ni-substituted distorted PFO lattices, while scanning electron microscopy and energy-dispersive spectroscopy indicated a uniform elemental distribution and surface morphology. Polarization vs. electrical field (P−E) measurements showed improved remnant polarization (Pr) with increasing Ni content and synthesis temperatures, achieving a maximum Pr of 66.7 µC/cm2 at 5 wt.% The Ni loading and substrate (Pt/Ti/SiO2/Si, Nanoshel Company, Cheshire, UK) temperature were 600 °C. These findings suggest that optimizing the synthesis parameters such as temperature and substitution content is crucial for controlling the ferroelectric properties of PFO thin films.

Sub-1 V/cm E-FISH-based picosecond electric field measurements in atmospheric pressure air

Abstract We report on the development of a highly sensitive Electric Field Induced Second Harmonic (E-FISH) generation diagnostic setup capable of measuring electric field strengths as low as 1 V/cm at the picosecond time scale under atmospheric pressure conditions. This unprecedented sensitivity is achieved through passive homodyne detection, which utilizes stray signals generated by an optical component in the beam path. Our detection limit of 0.3–0.5 V/cm represents an improvement of over 2–3 orders of magnitude compared to previous reports (100 – 1000 V/cm) in the literature. Additionally, we demonstrate sensitivity to the polarity of the electric field. Experimental results are corroborated by simulations of the 400 ps time-resolved homodyne process, offering deeper insights into the enhanced detection capabilities and the system’s ability to resolve the field sign.

Low-power electrodeless 2.45 GHz microwave plasma generation in ambient air with dielectric resonators

Abstract Microwave (MW) plasma, as an electrodeless non-thermal plasma technique, holds significant potential for gas processing applications under near-ambient conditions. However, current MW plasma methods suffer from low energy efficiency due to the high power required for molecular breakdown via vibrational excitation. A promising approach to mitigate this challenge involves using a pair of high relative permittivity dielectric resonators (DRs) in close proximity to enhance the electric field within the small gap between them, thus reducing power consumption. In this study, we combined simulations and experiments to investigate the electric field enhancement effect of DRs with varying shapes, geometrical parameters (e.g., radius and height), gap distances, and orientations relative to the electric field polarization and MW propagation directions. Simulations performed using Ansys HFSS demonstrate that edge-to-edge configurations of hexagonal, square, and triangular prism DRs can achieve significant electric field enhancement over a broad range of geometric parameters. DRs fabricated from calcium titanate were tested experimentally using a simple setup with a kitchen microwave (2.45 GHz) at ambient pressure. With input power below 100 W, stable and highly confined plasma was generated using hexagonal and triangular prism DRs. These results suggest a simple, cost-effective, and low-power method for generating MW plasma under ambient conditions, offering particular advantages for chemical processing in rural areas utilizing renewable energy resources.

Topological defects induced by air inclusions in ferroelectric nematic liquid crystals with ionic doping.

We report an experimental study on how topological defects induced by cylindrical air inclusions in the ferroelectric nematic liquid crystal RM734 are influenced by ionic doping, including an ionic surfactant and ionic polymer. Our results show that subtle differences in molecular structure can lead to distinct surface alignments and topological defects. The ionic surfactant induces a planar alignment, with two -1/2 line defects adhering to the cylindrical bubble surface. In contrast, the ionic polymer promotes homeotropic alignment, resulting in a -1 polar disclination around the cylindrical bubble. By numerical simulations, we verify that these topological defects are vertical lines with two dimensional polarization fields. These configurations differ from the boojums and hedgehog defects induced by air inclusions in nematic liquid crystals, highlighting the significant role of broken inversion symmetry.

Enhancing ionic conductivity and expanding the electrochemical window in polymer electrolytes via ferroelectric-metal-organic-frameworks to manipulate charge spatial distribution.

Poly (ethylene oxide) (PEO)-based polymer electrolytes have promising applications in all-solid-state lithium metal batteries. However, their wide range of practical applications is severely limited by their relatively low room temperature lithium ion conductivity and narrow electrochemical window. In this paper, based on the ability of spontaneous polarization of ferroelectric materials to generate polarization field under applied electric field and the characteristics of Metal-Organic-Frameworks (MOFs) materials with regular adjustable pore structure, a Nano material combining ferroelectric materials and MOF (NUS-6(Hf)-MOF) was first proposed to be added to PEO polymer electrolyte as a filler. NUS-6(Hf)-MOF can provide rapid transport channel for lithium ion, born under the applied electric field of the latter's consistent dipole polarization field can adjust the interface of the space charge distribution, the composite polymer electrolyte (NUSCPE) modified with NUS-6(Hf)-MOF has high ionic conductivity (1.16×10-3Scm-1) and lithium ion mobility (0.33) at 60°C. Simultaneously, the phenomenon of self-polarization causes the surface electronization, this results in a higher susceptibility to oxidation compared to PEO, thereby expanding the electrochemical window to 4.7V, and when paired with commercial LiNi0.8Co0.1Mn0.1O2 cathode, the capacity is maintained at 85% after 50 stable cycles at 0.2C at 60°C. The polymer electrolyte NUSCPE modified by NUS-6(Hf)-MOF provides a novel design idea for all solid-state lithium batteries with excellent electrochemical performance.

Strong Interfacial Interaction in Polarized Ferroelectric Heterostructured Nanosheets for Highly Efficient and Selective Photocatalytic CO2 Reduction.

Heterojunctions are sustainable solutions for the photocatalytic CO2 reduction reaction (CO2RR) by regulating charge separation behavior at the interface. However, their efficiency and product selectivity are severely hindered by the inflexible and weak built-in electric field and the electronic structure of the two phases. Herein, ferroelectric-based heterojunctions between polarized bismuth ferrite (BFO(P)) and CdS are constructed to enhance the interfacial interactions and catalytic activity. The intrinsic polarization field depending on the ferroelectric state causes significant electrostatic potential difference and energy-band bending. This helps overcome the unsatisfactory redox potential that differs from the classical catalytic mechanism, and synergy from the heterostructure facilitates effective separation and transfer of photogenerated charges with an extended lifetime (>20ns) and significantly enhanced photovoltage (1002 times that of BFO). The optimized charge carrier dynamics allow the heterojunction to achieve a much higher CO yield compared to state-of-the-art ferroelectric-based photocatalysts, and 85.46 and 23.47 times higher than those of pristine CdS and BFO, respectively. Moreover, it maintains an impressive 100% product selectivity together with excellent repeatability and cycling. This work not only sheds light on how a strong inherent polarity promotes the performance of heterojunction photocatalysts but also provides new insights for designing efficient photocatalytic CO2RR.

Dipolar wavevector interference induces a polar skyrmion lattice in strained BiFeO3 films.

Skyrmions can form regular arrangements, so-called skyrmion crystals (SkXs). A mode with multiple wavevectors q then describes the arrangement. While magnetic SkXs, which can emerge in the presence of Dzyaloshinskii-Moriya interaction, are well established, polar skyrmion lattices are still elusive. Here we report the observation of polar SkXs with a well-defined double-q state in ultrathin BiFeO3 films on LaAlO3. The compressive strain induced by the LaAlO3 substrate yields a dipolar topological texture with a periodic arrangement of skyrmions. The square-like superstructure with a lattice constant of 2.68 nm features a periodic modulation of polarization fields and topological charge density. The film furthermore exhibits an enhanced electromechanical response with an increased converse piezoelectric coefficient (d33) compared with SkX-free films. Transmission electron microscopy experiments in combination with phase-field simulations indicate that the dipole skyrmion texture results from the interference of two orthogonal single-q dipole patterns. We anticipate that the interference of multiple wavevectors may lead to a diversity of topological crystals with a variety of symmetries and lattice constants.