Antiparallel Field Research Articles

Topological confinement states in ABA trilayer graphene with antiparallel electric field

Topological confinement states in ABA trilayer graphene with antiparallel electric field

Design and Implementation of an Energy Selector for Laser-Accelerated Protons

Highly intense bunches of protons and ions with energies of several MeV/u can be generated with ultra-short laser pulses focused on solid targets. In the most common interaction regime, target normal sheath acceleration, the spectra of these particles are spread over a wide range following a Maxwellian distribution. We report on the design and testing of a magnetic chicane for the selection of protons within a limited energy window. This consisted of two successive, anti-parallel dipole fields generated by cost-effective permanent C-magnets with customized configuration and longitudinal positions. The chicane was implemented into the target vessel of a petawatt laser facility with constraints on the direction of the incoming laser beam and guidance of the outgoing particles through a vacuum port. The separation of protons and carbon ions within distinct energy intervals was demonstrated and compared to a ray tracing code. Measurements with radiochromic film stacks indicated the selection of protons within [2.4, 6.9] MeV, [5.0, 8.4] MeV, or ≥6.9 MeV depending on the lateral dispersion. A narrow peak at 4.8 MeV was observed with a time-of-flight detector.

Controllable spin transport in a zigzag silicene nanoribbon embedding multiple rectangular quantum dots

Based on the recursive Green-function method together with Landauer–Büttiker formalism, the spin-dependent transport properties of electrons in a zigzag silicene nanoribbon embedding multiple rectangular quantum dots (QDs) are investigated. According to an analysis of the energy band under the periodically distributed electric field and exchange ferromagnetic field, the parallel exchange field induced by the ferromagnetic insulators eliminates the spin degeneracy, which leads to spin-polarized transport in the proposed structure. By tuning a periodic electric field, we found the relationship between the number of QDs and the splitting peak for conductance in the anti-parallel exchange field. We discover the population of electrons near QDs by calculating the local density of states. The effect of the geometry of periodic QDs on the shift of resonance peak is evaluated. The spin polarization is further explored for various configurations of electric field and exchange field in order to manipulate the spin filtering more effectively. The results provide an avenue to design a controllable spin bandpass filter with the modulation of electric field and exchange field.

Nonequilibrium Ab Initio Molecular Dynamics Simulation of Water Splitting at Fe2O3-Hematite/Water Interfaces in an External Electric Field.

In the exploration of the optimal material for achieving the photoelectrochemical dissociation of water into hydrogen, hematite (α-Fe2O3) emerges as a highly promising candidate for proof-of-concept demonstrations. Recent studies suggest that the concurrent application of external electric fields could enhance the photoelectrochemical (PEC) process. To delve into this, we conducted nonequilibrium ab initio molecular dynamics (NE-AIMD) simulations in this study, focusing on hematite-water interfaces at room temperature under progressively stronger electric fields. Our findings reveal intriguing evidence of water molecule adsorption and dissociation, as evidenced by an analysis of the structural properties of the hydrated layered surface of the hematite-water interface. Additionally, we scrutinized intermolecular structures using radial distribution functions (RDFs) to explore the interaction between the hematite slab and water. Notably, the presence of a Grotthuss hopping mechanism became apparent as the electric field strength increased. A comprehensive discussion based on intramolecular geometry highlighted aspects such as hydrogen-bond lengths, H-bond angles, average H-bond numbers, and the observed correlation existing among the hydrogen-bond strength, bond-dissociation energy, and H-bond lifetime. Furthermore, we assessed the impact of electric fields on the librational, bending, and stretching modes of hydrogen atoms in water by calculating the vibrational density of states (VDOS). This analysis revealed distinct field effects for the three characteristic band modes, both in the bulk region and at the hematite-water interface. We also evaluated the charge density of active elements at the aqueous hematite surface, delving into field-induced electronic charge-density variations through the Hirshfeld charge density analysis of atomic elements. Throughout this work, we drew clear distinctions between parallel and antiparallel field alignments at the hematite-water interface, aiming to elucidate crucial differences in local behavior for each surface direction of the hematite-water interface.

Electric field induced tunable half-metallicity in an A -type antiferromagnetic bilayer LaBr2

How to achieve half-metallicity is always a central topic in spintronics and the polarity-tunable half-metallicity is particularly interesting for spin manipulation. In this work, motivated by the intrinsic ferromagnetism in the monolayer electride ${\mathrm{LaBr}}_{2}$, based on density functional theory calculations, we investigate the electronic and magnetic properties of bilayer ${\mathrm{LaBr}}_{2}$, with an aim to search for polarity-tunable half-metallicity. We first find that the antiferromagnetic interlayer coupling state is the ground state and the band structure is spin degenerate, with an indirect band gap of 0.454 eV. By applying a vertical electric field, spin splitting occurs and when the electric field is strong enough ($\ensuremath{\ge}0.33$ V/\AA{}), half-metallicity can be achieved. More interestingly, the spin polarity of the half-metallicity can be tuned by reversing the electric field direction. It originates from the spatial separation of the two spin channels in both the valence band and conduction band and their localization at different layers. Based on the polarity-tunable half-metallicity under vertical electric field, a magnetic tunnel junction based on bilayer ${\mathrm{LaBr}}_{2}$ is designed and the ON/OFF switching can be achived by applying parallel or anti-parallel vertical electric fields in the two leads, which leads to giant tunnel magnetoresistance up to $1\ifmmode\times\else\texttimes\fi{}{10}^{6}$. The findings suggest new potential of ${\mathrm{LaBr}}_{2}$, and more generally, $A$-type antiferromagnets of application in spintronic devices.

Tailoring permittivity using metasurface: a facile way of enhancing extreme-angle transmissions for both TE- and TM-polarizations.

The transmission of electromagnetic (EM) waves through a dielectric plate will be decreased significantly when the incident angle becomes extremely large, regardless of transverse electric (TE)- or transverse magnetic (TM)- polarization. In this regard, we propose a facile way of tailoring the permittivity of the dielectric material using metasurface to enhance the transmissions of both TE- and TM-polarized waves under extremely large incidence angles. Due to parallel or antiparallel electric fields induced by the metasurface, the net electric susceptibility is altered, and hence the effective permittivity can be tailored to improve the impedance matching on the two air-dielectric interfaces, which enhances the wave transmissions significantly under extreme incident angles. As an example, we apply this method to a typical ceramic-matrix composite (CMC) plate. By incorporating orthogonal meta-gratings into the CMC plate, its effective permittivity is reduced for the TE-polarized waves but increased for the TM-polarized waves under the extreme incidence angle, which can reduce the impedance for the TE-polarization and increase the Brewster angle for the TM-polarization. Therefore, the impedance matchings for both TE- and TM-polarizations are improved simultaneously and dual-polarized transmission enhancements are achieved under the extreme angles. Here, the transmission responses have been numerically and investigated using the finite-difference-time-domain (FDTD) method. A proof-of-principle prototype is designed, fabricated, and measured to verify this method. Both numerical simulations and measurement results show that the prototype can operate under extremely large incidence angles θi∈[75°,85°] with significant transmission enhancement for both TE- and TM-polarizations compared to the pure dielectric plate. This work provides a facile way to enhance the transmissions under extreme angles and can be readily extended to terahertz and optical frequencies.

Vortex lattices in binary Bose–Einstein condensates: collective modes, quantum fluctuations, and intercomponent entanglement

We study binary Bose–Einstein condensates subject to synthetic magnetic fields in mutually parallel or antiparallel directions. Within the mean-field theory, the two types of fields have been shown to give the same vortex-lattice phase diagram. We develop an improved effective field theory to study properties of collective modes and ground-state intercomponent entanglement. Here, we point out the need to introduce renormalized coupling constants for coarse-grained densities. We show that the low-energy excitation spectra for the two types of fields are related to each other by suitable rescaling with the renormalized coupling constants. By calculating the entanglement entropy, we find that for an intercomponent repulsion (attraction), the two components are more strongly entangled in the case of parallel (antiparallel) fields, in qualitative agreement with recent studies for a quantum (spin) Hall regime. We also find that the entanglement spectrum exhibits an anomalous square-root dispersion relation, which leads to a subleading logarithmic term in the entanglement entropy. All of these are confirmed by numerical calculations based on the Bogoliubov theory with the lowest-Landau-level approximation. Finally, we investigate the effects of quantum fluctuations on the phase diagrams by calculating the correction to the ground-state energy due to zero-point fluctuations in the Bogoliubov theory. We find that the boundaries between rhombic-, square-, and rectangular-lattice phases shift appreciably with a decrease in the filling factor.

Electron‐Only Reconnection as a Transition Phase From Quiet Magnetotail Current Sheets to Traditional Magnetotail Reconnection

AbstractIn Earth's magnetotail, we report three types of current sheets: Quiet current sheets supported by antiparallel lobe fields, “electron‐only” reconnecting current sheets, and traditionally reconnecting current sheets. We survey Earth's magnetotail for each current sheet type and perform event studies on one of each. One quiet current sheet, three electron‐only reconnecting current sheets, and one traditionally reconnecting current sheet are placed in order to showcase the possible time‐evolution of reconnection onset. Over time, electron‐only reconnecting current sheets increase in thickness, electron and ion outflow exhaust, perpendicular ion temperature, parallel electron temperature, and Hall electric field. These features support a transition phase from a quiet current sheet to traditional reconnection. Statistics of each current sheet type show that, during electron‐only reconnection, electrons are heated and evacuate the reconnection region while ions retain the properties of a quiet current sheet. In addition, statistics of solar wind properties indicate that electron‐only and traditional reconnection do not have unique solar wind drivers. Guide field statistics of electron‐only reconnection imply that aspects of the driving mechanism of electron‐only reconnection remain unclear.

Electron energization during merging of self-magnetized, high-beta, laser-produced plasmas

Electron energization during merging of magnetized plasmas is studied using the OMEGA and OMEGA EP laser facilities by colliding two plasma plumes, each containing a Biermann-battery self-generated magnetic field. Two neighbouring plasma plumes are produced by intense laser beams, and the anti-parallel Biermann fields merge and reconnect in the process of the plumes’ expansion and collision. To isolate the merging as an acceleration source, the electron energy spectra obtained from two-plume collision shots are compared with the spectra from single-plume shots. Single-plume shots exhibit an energized electron tail with energies up to ${\sim }250\ \textrm {keV}$ . The electrons in merging experiments are additionally accelerated by ${\sim }50\text {--}100$ keV compared to single-plume shots.

Hall instability: origin, properties and asymptotic theory for its tearing mode

Hall instability in electron magnetohydrodynamics is interpreted as the shear-Hall instability driven jointly by helicoidal oscillations and shear in the electron current velocity. This explanation suggests an antiparallel orientation of the background magnetic field and vorticity of the current velocity as the necessary condition for Hall instability. The condition is tested and generally confirmed by numerical computations in plane slab geometry. Unstable eigenmodes are localized in the spatial regions of the antiparallel field and vorticity. Computations of the tearing-type mode of the instability are complemented by (and generally agree with) asymptotic analytical estimations for large Hall numbers. The stabilizing effect of perfect conductor boundary conditions is found and explained. For large Hall numbers, the growth rates approach the power-law dependence$\sigma \propto B^\alpha \eta ^{1-\alpha }$on the magnetic field ($B$) and diffusivity ($\eta$). Almost all computations give the power index$\alpha = 3/4$with one exception of the tearing-type mode with vacuum boundary conditions for which case$\alpha = 2/3$.

Mesoscopic models for electrohydrodynamic interactions of polyelectrolytes

Two mean-field models for polyelectrolytes in simultaneous electric field and pressure-driven flow field were developed and compared. The models predict migration perpendicular to the anti-parallel or parallel fields, where the migration is caused by electrohydrodynamic interactions calculated using either a short- or long-range approximation. Inputs for the mean-field models were determined from Brownian dynamics simulations in a simple shear flow. Both models qualitatively reproduce experimental observations of DNA focusing as reported in previous publications. Specifically, it is observed that combination of the shear and electric fields leads to polyelectrolyte motion in the direction transverse to the flow and electric field direction, which in turn leads to concentration of the polyelectrolyte in the centre of a microfluidic channel. Furthermore, both models predict that there is an optimal strength of electric field that leads to the narrowest distribution profile of the polyelectrolyte in the centre of the channel. The analysis suggests that this is due to dispersion induced by the electrohydrodynamic interactions. However, quantitative disagreement between the model predictions and the experimental data indicates that further progress in the model development is needed.

Magnetic knot cascade via the stepwise reconnection of helical flux tubes

Abstract

Quantum-confined Stark effect and mechanisms of its screening in InGaN/GaN light-emitting diodes with a tunnel junction.

Nitride-based light-emitting diodes (LEDs) are well known to suffer from a high built-in electric field in the quantum wells (QWs). In this paper we determined to what extent the electric field is screened by injected current. In our approach we used high pressure to study this evolution. In LEDs with a narrow QW (2.6 nm) we found that even at a high injection current a large portion of built-in field remains. In LEDs with very wide QWs (15 and 25 nm) the electric field is fully screened even at the lowest currents. Furthermore, we examined LEDs with a tunnel junction in two locations - above and below the active region. This allowed us to study the cases of parallel and antiparallel fields in the well and in the barriers.

Tunable spin-photovoltaic effect in zigzag MoS2 nanoribbons

This article introduces a method for generating spin-polarized photocurrent through light radiation on zigzag MoS2 nanoribbons. In this regard, we investigate local manipulation by exposing edge states to (i) a ferromagnetic, (ii) an antiferromagnetic exchange field, (iii) a parallel and an antiparallel electric field. These local manipulations at the edges with intrinsic spin-orbit interaction could produce a spin-polarized photocurrent and manipulate optical properties. Even at one edge of the nanoribbon, applying the exchange field could induce a fully spin polarization by light irradiation. Efficient quantum efficiency, significant optical spin polarization, and spin-polarized photocurrent make zigzag MoS2 nanoribbon an effective structure for improving the performance of spin-photovoltaic devices.

Memory Effect in Antiferroelectrics: A Systematic Analysis on Various Electric Hysteresis Loops

Antiferroelectric materials are proposed as a potential solution to achieve multi-state memories, but the fundamental physical mechanism underlying the memory effect still needs to be clarified. Here, we study the memory effect in a typical antiferroelectric ceramic of Pb0.99Nb0.02[(Zr0.6Sn0.4)0.95Ti0.05]0.98O3 by systematically analyzing various hysteresis loops of polarization intensity and current density vs. electric field, where the kinetic behaviors are concerned about for the first time. The parallel pre-poling electric field reduces the critical electric field of antiferroelectric-ferroelectric phase transition, while the antiparallel field increases it. The memory behavior is significantly enhanced with the increasing of pre-poling time, but exhibits a remarkable weakening with the relaxation time increasing. It is a combined effect of electric-field-induced preferentially oriented antiferroelectric domains and internal bias electric field. This work not only improves comprehending in memory effect in antiferroelectric materials, but also enlightens the deeper understanding of other physical properties related to field-induced phase transitions.

Memory effect in antiferroelectrics: A systematic analysis on various electric hysteresis loops

Antiferroelectric materials are proposed as a potential solution to achieve multi-state memories, but the fundamental physical mechanism underlying the memory effect still needs to be clarified. Here, we study the memory effect in a typical antiferroelectric ceramic of Pb0.99Nb0.02[(Zr0.6Sn0.4)0.95Ti0.05]0.98O3 by systematically analyzing various hysteresis loops of polarization intensity and current density vs. electric field, where the kinetic behaviors are concerned about for the first time. The parallel pre-poling electric field reduces the critical electric field of antiferroelectric-ferroelectric phase transition, while the antiparallel field increases it. The memory behavior is significantly enhanced with the increasing of pre-poling time, but exhibits a remarkable weakening with the relaxation time increasing. It is a combined effect of electric-field-induced preferentially oriented antiferroelectric domains and internal bias electric field. This work not only improves comprehending in memory effect in antiferroelectric materials, but also enlightens the deeper understanding of other physical properties related to field-induced phase transitions.

Particle acceleration by interstellar plasma shock waves in non-uniform background magnetic field

ABSTRACTParticle acceleration by plasma shock waves is investigated for a magnetized plasma cloud propagating in a non-uniform background magnetic field by means of analytical and numerical calculations. The mechanism studied here is mainly, magnetic trapping acceleration (MTA) which is previously investigated for a cloud moving through the uniform interstellar magnetic field (IMF). In this work, the acceleration is studied for a cloud moving in an antiparallel background field with spatial variations along the direction of motion. For negative variation, the cloud moves towards an antiparallel magnetic field with an increasing intensity, the trapped particle moves to locations with higher convective electric field and therefore gains more energy over time. For positive variation, the background field decreases to zero and changes into a parallel field with an increasing intensity. It is concluded that, when the background field vanishes, the MTA mechanism ceases and the particle escapes into the space. This leads to a bouncing acceleration which further increases energy of the gyrating particle. The two processes are followed by a shock drift acceleration, where due to the background magnetic field gradient, the particle drifts along the electric field and gains energy. Although for positive variation, three different mechanisms are involved, energy gain is less than in the case of a uniform background field.

Influence of domain switching process on the electrical fatigue behavior of ferroelectrics

We report an experimental approach, designed based on the recent findings that domain switching in ferroelectric ceramics can be separated into three regimes during antiparallel electric field loading, to investigate the influence of domain switching process on the electrical fatigue behavior of ferroelectrics. Uniaxial compressive stress (−2 MPã -100 MPa) and thermal loading (20 °C–150 °C) were used to tune the domain switching process. Under the same loading condition, the bipolar electrical fatigue behavior of soft lead zirconate titanate ceramics was systematically characterized. The amplitude and frequency of the applied electric field are 2 kV/mm and 10 Hz, respectively. By analyzing the evolution of the domain switching process, combined with the measured polarization and strain response, as well as the cracks observed on the surface of the specimen, it is found that the fatigue of ferroelectric ceramics was mainly related to the domain switching process near the coercive electric field: the regime 2 defined in this paper. The underlying mechanism was further discussed by considering the interplay between the domain switching process with the main factors affecting the electrical fatigue of ferroelectrics, namely defect redistribution, charge carrier injection, and crack initiation.

Reversible edge spin currents in antiferromagnetically proximitized dichalcogenides

We explore proximity effects on transition metal dichalcogenide ribbons deposited on antiferromagnetic (AFM) insulating substrates. We model these hybrid heterostructures using a tight-binding model that incorporates exchange and Rashba fields induced by proximity to the AFM material. The robust edge states that disperse in the midgap of the dichalcogenide are strongly affected by induced exchange fields that reflect different AFM ordering in the substrate. This results in enhanced spin-orbit coupling effects and complex spin projection content for states on zigzag ribbon edges. Gated systems that shift the Fermi level in the midgap range are also shown to exhibit spin-polarized currents on these edges. Antiparallel exchange fields along the edge results in spin currents that can reverse polarization with the applied field. The added functionality of these hybrid structures can provide spintronic devices and versatile platforms to further exploit proximity effects in diverse material systems.

Trapped magnetic field distribution above two magnetized bulk superconductors close to each other

Bulk large-grain superconductors can be used as high-field permanent magnets. Although the properties of such individual trapped field magnets are well documented, much less is known concerning their behaviour when two are brought together. In this work, the interaction between two cylindrical bulk YBa2Cu3O7 (YBCO) superconductors is described. Two sets of experiments were carried out. The first involved the simultaneous magnetization of two bulk superconductors placed a short distance apart. Here, the applied magnetic field was aligned parallel to the c-axis of one bulk, while the other was oriented with its c-axis offset . For a centre-to-centre distance equal to twice the sample height, the presence of the second sample is found not to alter the current distribution inside the first. Consequently, the contribution of both samples simply sums, thus increasing the magnetic flux density between them. In the second set of experiments, the translational approach of the superconductors with parallel c-axes was investigated. The following configurations were considered: (i) face to face approach (with anti-parallel trapped field orientation) and (ii) sideways approach (with parallel trapped field orientation). An irreversible decrease of the trapped field was measured on separation . Repeated approach cycles showed that the irreversible loss of trapped field is largest for the first approach.