External Field Research Articles

Mechanistic Studies of Stimulus-Response Integrated Catalysis of Single-Atom Alloys under Electric Fields for Electrochemical Nitrogen Reduction.

The present work introduces a novel catalytic strategy to promote the nitrogen reduction reaction (NRR) by employing a cooperative Cu-based single-atom alloy (SAA) and oriented external electric fields (OEEFs) as catalysts. The field strength (F)-dependent reaction pathways are investigated by means of first-principle calculations. Different dipole-induced responses of intermediates to electric fields break the original scaling relationships and effectively tune not only the activity but also the product selectivity of the NRR. When the most active Os1Cu SAA is taken as an example, in the absence of an OEEF, the overpotential (η) of the NRR is 0.62 V, which is even larger than that of the competitive hydrogen evolution reaction (HER). A negative field not only reduces η but switches the preference to the NRR over the HER. In particular, η at F = -1.14 V/Å reaches the bottom of 0.18 V, which is 70% lower than that in the field-free state.

Infinite (continuous) spin particle in constant curvature space

We present a new particle model that generalize for constant curvature space an infinite spin particle in flat space. The model is described by commuting Weyl spinor additional coordinates. It proved that such a model is consistent only in external gravitational field corresponding to the constant curvature spaces. Full set of the first-class constraints in the de Sitter and anti-de Sitter spaces is obtained.

Generation of localized, half-frequency spin waves in micron sized ferromagnetic stripes: Experiments and simulations

Generation of localized, half-frequency spin waves in micron sized ferromagnetic stripes: Experiments and simulations

Giant dielectric tunability in ferroelectric ceramics with ultralow loss by ion substitution design

Due to their responsiveness to modulation by external direct current fields, dielectric tunable materials are extensively utilized in integrated components, such as ferroelectric phase shifters. Barium strontium titanate ceramics have been considered the most potential tunable materials for a long time. However, the significant dielectric loss and high voltage drive have limited their further applications. Recently, Bi6Ti5WO22 ceramic has regained attention for its high dielectric tunability with low loss. In this study, we judiciously introduce Nb5+ with a larger ionic radius, replacing Ti4+ and W6+. This successful substitution enables the modulation of the phase transition temperature of Bi6Ti5WO22 ceramics to room temperature, resulting in superior tunable properties. Specifically, the 0.7Bi6Ti5WO22−0.3Bi6Ti4Nb2O22 ceramics exhibit giant tunability (~75.6%) with ultralow loss (<0.002) under a low electric field (1.5 kV/mm). This tunability is twice that of barium strontium titanate ceramics with a similar dielectric constant and only one-tenth of the loss. Neutron powder diffraction and transmission-electron-microscopy illustrate the nanodomains and micro-strains influenced by ion substitution. Density functional theory simulation calculations reveal the contribution of ion substitution to polarization. The research provides an ideal substitute for tunable material and a general strategy for adjusting phase transition temperature to improve dielectric properties.

Effects of Nanowire Doping on Plasmon-Enhanced N2 Dissociation.

Doping a transition metal element into plasmonic systems can tune the optical properties of the system, which will potentially facilitate the plasmon-enhanced catalytic process. In this study, we applied the linear-response time-dependent density functional theory (LR-TDDFT) method with real-time electron dynamics and mean-field Ehrenfest dynamics methods to computationally investigate the effects of doping silver nanowires on plasmon-enhanced N2 dissociation. We calculated the absorption spectra for different doped systems, applied an external electric field to the system, and performed mean-field Ehrenfest dynamics to examine how plasmonic excitation will affect the N2 activation or dissociation. In addition, we also studied how the transition metal dopant affects the system's electronic structure and potential energy surface.

Realization of fractional quantum Hall state with interacting photons.

Fractional quantum Hall (FQH) states are known for their robust topological order and possess properties that are appealing for applications in fault-tolerant quantum computing. An engineered quantum platform would provide opportunities to operate FQH states without an external magnetic field and enhance local and coherent manipulation of these exotic states. We demonstrate a lattice version of photon FQH states using a programmable on-chip platform based on photon blockade and engineering gauge fields on a two-dimensional circuit quantum electrodynamics system. We observe the effective photon Lorentz force and butterfly spectrum in the artificial gauge field, a prerequisite for FQH states. After adiabatic assembly of Laughlin FQH wave function of 1/2 filling factor from localized photons, we observe strong density correlation and chiral topological flow among the FQH photons. We then verify the unique features of FQH states in response to external fields, including the incompressibility of generating quasiparticles and the smoking-gun signature of fractional quantum Hall conductivity. Our work illustrates a route to the creation and manipulation of novel strongly correlated topological quantum matter composed of photons and opens up possibilities for fault-tolerant quantum information devices.

The origin of the spontaneous polarization of CaBi2Nb2O9: The polarization of the two layers and their coupling mechanisms

The first-principles calculations are employed to investigate the origin of the spontaneous polarization (Ps) of CaBi2Nb2O9 (CBNO), composing of the perovskite-like (CaNb2O7)2- layer (CNO) and the fluorite-like (Bi2O2)2+ layer (BO). The Ps along the a-axis exists in the both of the CNO and BO layers, and the direction of the Ps along the a-axis of the two layers is the same, their contribution to the Ps of the ferroelectric phase is almost same. Moreover, the experimental results (12.00 μC/cm2) are about half value of our calculated the Ps (28.67 μC/cm2) and previous calculated (24.40 μC/cm2). The difference between the experiments and the theoretical calculations may be cause by the reason that only the polarization in the CNO layer can switch under the external electric field. Meanwhile, the stable crystal structure of the BO layer result in the polarization cannot switch. Therefore, the polarization of the BO layer does not contribute the remnant polarization. The inter-layer coupling between the CNO and BO layers of the ferroelectric phase enhances the Ps along the a-axis. In addition, the Ps along the c-axis of the two layers is almost same, however, their direction is opposite, as is similar to the anti-ferroelectrics.

Oversaturating Liquid Interfaces with Nanoparticle‐Surfactants

AbstractAssemblies of nanoparticles at liquid interfaces hold promise as dynamic “active” systems when there are convenient methods to drive the system out of equilibrium via crowding. To this end, we show that oversaturated assemblies of charged nanoparticles can be realized and held in that state with an external electric field. Upon removal of the field, strong interparticle repulsive forces cause a high in‐plane electrostatic pressure that is released in an explosive emulsification. We quantify the packing of the assembly as it is driven into the oversaturated state under an applied electric field. Physiochemical conditions substantially affect the intensity of the induced explosive emulsification, underscoring the crucial role of interparticle electrostatic repulsion.

Applied electric field induced the change of spin-electron of the Fe3GeTe2 to improve its oxygen evolution reaction performance

Utilizing density functional theory (DFT) calculations, we investigate the influence of the external electric field on the oxygen evolution reaction (OER) performance of monolayer Fe3GeTe2. Monolayer Fe3GeTe2 has ferromagnetic metal properties and displays excellent electrocatalytic activity. The magnetism mainly comes from FeI atoms, owing to the strong Fe-Te orbitals hybridization, and FeI atoms have great effect on the active site Te atoms. The electric field induces the change of spin-electron and promotes charge redistribution in the Fe3GeTe2, resulting in the changes of the magnetic moment and magnetic anisotropic energy (MAE). Simultaneously, the applied electric field shifts the energy band and decreases the work function which facilitates carrier migration to the surface. Therefore, the OER overpotential is reduced and the catalytic performance is improved. These valuable findings can serve as vital references for the design of 2D magnetic electrocatalysts.

Efficient reverse water gas shift reaction at low temperatures over an iron supported catalyst under an electric field

The development of high-performance Fe-based catalysts is attractive because Fe is a cost-effective and earth-abundant element. Application of an external electric field and an appropriate catalytic support to an Fe-based catalyst enabled the reverse water–gas shift reaction to proceed with high activity, selectivity, and durability even at the low temperature of 423 K. The Fe-supported catalyst showed superior CO selectivity (≈ 100%) compared to the Co- or Ni-supported catalyst. The apparent activation energy (5.9 kJ mol−1) over the Fe/Ce0.4Al0.1Zr0.5O2 catalyst under an electric field was much lower than that without an electric field (61.4 kJ mol−1).

Oversaturating Liquid Interfaces with Nanoparticle-Surfactants.

Assemblies of nanoparticles at liquid interfaces hold promise as dynamic "active" systems when there are convenient methods to drive the system out of equilibrium via crowding. To this end, we show that oversaturated assemblies of charged nanoparticles can be realized and held in that state with an external electric field. Upon removal of the field, strong interparticle repulsive forces cause a high in-plane electrostatic pressure that is released in an explosive emulsification. We quantify the packing of the assembly as it is driven into the oversaturated state under an applied electric field. Physiochemical conditions substantially affect the intensity of the induced explosive emulsification, underscoring the crucial role of interparticle electrostatic repulsion.

Electronic and optical properties and electrocatalytic water splitting in a graphene/MoS2 heterojunction

The electronic and optical properties of graphene/MoS2 heterojunction were investigated by the First-principles. The Dirac cone in this heterojunction opens about 11 meV. The contact type of graphene/MoS2 heterojunction could be changed from Schottky to Ohmic contact under the external electric field. The external electric field could also effect the band alignment and orbital coupling in this heterojunction. In addition, we investigate water splitting of electrocatalysis in this heterojunction. We find that the surface of MoS2 has better performance in the hydrogen evolution reaction. The surface of graphene in this heterojunction has lower over potential in the oxidation evolution reaction. Moreover, the optical properties are also improved in this heterojunction. This paper could provide a theoretical basis for the application of graphene/MoS2 heterojunction in the field of nanodevices and electrocatalysis.

Photon-assisted destructive interference through a parallel-coupled double quantum dots

In this paper, we establish a model to realize the photon-assisted destructive interference phenomena, the model consisting of parallel-coupled double quantum dots and Luttinger liquid leads. By applying the canonical transformation and the nonequilibrium Green’s function technique, the general time-dependent current formula is developed. The joint effects of the intralead Coulomb interaction and an external ac field on the quantum interference are investigated. For weak intralead interactions, besides the usual photon-assisted tunneling resonance, there are two types of photon-assisted tunneling destructive interference: one is related to interdot coupling and the other to intralead interactions. For moderately strong intralead interaction, the photon-assisted sidebands are suppressed and the differential conductance scales as a power law in bias voltage. In particular, we show the multiphoton absorption and emission up to four photons in an electron tunneling process. We believe that the photo-assisted destructive interference results obtained in this paper are instructive for future experiments.

The recent star formation histories of nearby galaxies on resolved scales

Abstract Star formation histories (SFHs) of galaxies are affected by a variety of factors, both external (field vs. cluster/group) and internal (presence of a bar and AGN, morphological type). In this work, we extend our previous study and apply the $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ metric to a sample of eleven nearby galaxies with MUSE observations. Based on a combination of Hα and UV photometry, $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ is sensitive to star formation timescales of ∼5–200 Myr and therefore measures the present-day rate of change in the star formation rate, dSFR/dt. Within this limited galaxy sample, we do not observe systematic variations between the global value of $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ and the presence of an active galactic nucleus, stellar bar, nor with group or cluster membership. Within some of the individual galaxies, we however observe significant differences in $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ between the arm and interarm regions. In half of the galaxies, the recent SFH of both arm and interarm regions has been very similar. However, in the galaxies with higher bulge-to-total light ratios and earlier morphological type, the SFR is declining more rapidly in the interarm regions. This decline in SFR is not a result of low molecular gas surface density or a decrease in the star formation efficiency, implying that other factors are responsible for this SFR decrease.

A spin current detecting device working in the drift-diffusion and degenerate regimes

&lt;p&gt;A semiconductor-based device working in the spin drift-diffusion regime and for probing the injected or generated spin current was considered. The electric field effects on spin transport were analysed. A drift-diffusion equation for spin density was derived and contributions to the spin current were examined. By referring to the techniques of the spin current injection and generation, expressions for the spin current and spin-induced transverse Hall voltage arising from the injected or generated spin-polarized current were derived. The spin current and Hall voltage in dependences of the external electric field and temperature in the degenerate regime were studied. The device operated on the basis of with no external magnetic fields gives a voltage probe of the spin-induced Hall effect. Finally, a way of enhancing the spin current was explored.&lt;/p&gt;

Gaining Insights into the Interplay between Optical and Magnetic Properties in Photoexcited Coordination Compounds.

We describe early and recent advances in the fascinating field of combined magnetic and optical properties of inorganic coordination compounds and in particular of 3d-4f single molecule magnets. We cover various applied techniques which allow for the correlation of results obtained in the frequency and time domain in order to highlight the specific properties of these compounds and the future challenges towards multidimensional spectroscopic tools. An important point is to understand the details of the interplay of magnetic and optical properties through performing time-resolved studies in the presence of external fields especially magnetic ones. This will enable further exploration of this fundamental interactions i.e. the two components of electromagnetic radiation influencing optical properties.

Joining of single-core ex-situ MgB2/Fe wires by termination architecture

The development of reliable jointing technique is of great importance for the future of applied superconductivity, especially for superconducting magnets working in persistent mode. Superconducting joints with termination architecture between single-core not reacted ex-situ MgB2/Fe wires were manufactured and tested. I-V characteristics of joints were measured at 4.2 K and 20 K for variable external fields and compared with I-V of joined wire. The ratio of joints critical current to that of parent conductors (Ic-joint/Ic-wire) has been evaluated and discussed. It was found that Ic-joint with termination architecture may be even larger than Ic-wire at high external field, but decreasing for lower fields. Ic-joint/Ic-wire = 0.8 was measured for the best joint at 20 K and low external field 1.5 T, which is promising for functional persistent switch.

Non-conventional resonant behavior of an unconfined magnetic domain wall in a permalloy strip

The resonant dynamic of a magnetic domain wall in a permalloy microstrip has been investigated using an innovative experimental setup that enables a simultaneous measurement of the ferromagnetic resonance and the magnetoresistance. The resonance frequency associated with the presence of the magnetic domain wall increases linearly with the external magnetic field in the range of fields where the domain wall is present in the microstrip. This linear behavior is unusual in a domain wall and not related to the standard resonant modes of a magnetic domain wall, such as breathing, twisting, or translational modes. The slope of this linear dependency is 1.38 GHz/mT, which is an incredibly large value and allows the detection of very small changes in the external magnetic field. This linear behavior opens a path for developing a highly tunable radio frequency oscillator or a magnetic sensing device where the presence of an external field is detected via small variations in the resonant frequency of the domain wall.

Tuning phase structure for enhanced electrostrain in Nb5+-doped Bi0.5(Na0.81K0.19)0.5TiO3 lead-free piezoelectric ceramics

The synthesis of Bi0.5(Na0.81K0.19)0.5Ti1−xNbxO3 (BNKT-xNb) lead-free piezoelectric ceramics via the traditional solid-state method, with varying x from 0.5 % to 4.0 %, is reported. Investigating the influence of Nb5+ ions on dielectric, ferroelectric, and electrostrain properties, alongside assessing the temperature stability of electrical properties, unveiled a notable electrostrain of 0.46 % at room temperature under 80 kV/cm for the 2.0 mol.% Nb5+ doped composition. The incorporation of Nb5+ prompted a transition from the ferroelectric to the relaxor phase, facilitating reversible induction into the ferroelectric phase under an external electric field, leading to the observed large electrostrain. Leveraging the first-order reversal curve (FORC) approach, a detailed analysis of the dynamic response process of different phase structures under the influence of the external electric field was conducted. This analysis elucidated that the continuous polarization response near the boundary of ferroelectric and relaxor phases, induced by the external electric field, primarily drives strain enhancement. These findings underscore the effective modulation of phase structure through Nb5+ doping, offering significant advancements in strain properties. This study opens avenues for the utilization of the material in micro actuators and provides valuable insights for the development of high-performance lead-free piezoelectric ceramics.

The Fermi-LAT view of the changing-look blazar OQ 334

Context. Unusually, there are still certain characteristics of the changing-look (CL) active galactic nuclei (AGNs) that remain undetected. Consequently, the trigger mechanism behind the CL phenomenon observed in partial AGNs remains unknown. Aims. We explore the light curve and spectral energy distribution (SED) of the CL blazar OQ 334 as obtained by Fermi-LAT. Methods. By examining the variability of the equivalent width (EW), we categorise the Fermi-LAT light curves of OQ 334 during the epoch of MJD 54628−58677 into seven distinct epochs, including the flat spectrum radio quasar (FSRQ) state, the transition state, and the BL Lac state. We obtained both a Fermi-LAT SED and a multi-wavelength SED for each of these distinct epochs. Results. The source exhibits a transformation from a quiescent state to a highly active state, as evidenced by the variability of the EW. The multi-wavelength SEDs display a prominent external Compton characteristic, even though the Fermi-LAT SED reveals both a FSRQ and a BL Lac state across the seven different epochs. To gain further insights, we employed a leptonic model that takes into account the soft photon fields originating from both synchrotron radiation and the external environment. By simulating the multi-wavelength SEDs for each epoch, we uncover the following results. Firstly, the energy density of the external photon fields evolves in an oscillatory manner over the seven different epochs. Also, the energy density of the external photon fields in the BL Lac state is lower than that in the FSRQ state. Conclusions. These findings suggest that the CL blazar represents a unique phase in the blazar sequence. Considering that the energy density of the external photon fields is proportional to the accretion rate, we propose that evidence for the interconversion of advection-dominated accretion flow (ADAF) discs and standard Shakura–Sunyaev discs (SSDs), – as variations in accretion modes in the CL blazar – can be obtained through observations by Fermi-LAT.