Presence Of External Electric Field Research Articles

Emergent gravity and chiral anomaly in Dirac semimetals in the presence of dislocations

We consider the recently discovered Dirac semimetals with two Dirac points ±K. In the presence of elastic deformations each fermion propagates in a curved space, whose metric is defined by the expansion of the effective Hamiltonian near the Dirac point. Besides, there is the emergent electromagnetic field that is defined by the shift of the Dirac point. We consider the case, when the deformations are caused by the dislocations. The dislocation carries singular torsion and the quantized flux of emergent magnetic field. Both torsion singularity and emergent magnetic flux may be observed in the scattering of quasiparticles on the dislocation due to Stodolsky and Aharonov–Bohm effects. We discuss quantum anomalies in the quasiparticle currents in the presence of emergent gauge and gravitational fields and the external electromagnetic field. In particular, it is demonstrated, that in the presence of external electric field the quasiparticles/holes are pumped from vacuum along the dislocation. The appeared chiral imbalance along the dislocation drives the analogue of chiral magnetic effect, that is the appearance of electric current along the dislocation.

DFT studies on hydrogen-bonding, Stacking, and XH···π-Bonded systems in presence of external electric field

Effect of external electric field on interaction energy as well as stability of the hydrogen-bonding, stacking, and OH π-bonded systems are analyzed in the light of density functional theory (DFT) and conceptual DFT. Interaction energy and stability measured in terms of global hardness and highest occupied molecular orbital energy of the considered systems are observed to be sensitive toward the strength and direction of the applied external electric field. The curvature of the potential energy surfaces gets changed in presence of an external electric field. © 2015 Wiley Periodicals, Inc.

In-situ combined dual-layer CNT/PVDF membrane for electrically-enhanced fouling resistance

Electrically conductive membrane possesses a remarkable performance in antifouling with the assistance of applied external electric fields. However, its widespread application is hampered due to the poor properties of existing conductive membranes, such as low conductivity and inadequate strength. The present study demonstrates a novel in-situ combination approach for the fabrication of a highly conductive carbon nanotube (CNT)/polyvinylidene fluoride (PVDF) membrane. During membrane fabrication, the casting solution film was pre-mantled with a CNT layer before the occurrence of polymer precipitation, thereby ensuring a natural and tight in-situ mergence between the CNT layer and supporting PVDF. The obtained CNT/PVDF membrane was characterized in terms of physicochemical properties and filtration performance. An electrically-enhanced cross-flow filtration system was devised to evaluate the antifouling performance of the pristine PVDF and CNT/PVDF membranes. Compared with the pristine PVDF membrane, the CNT/PVDF membrane possesses a greater electrical conductivity and a higher permeability. The incorporation of the CNT layer led to a completely different surface composition in terms of elemental components and functional groups. Being used as a cathode, the CNT/PVDF membrane exhibited a remarkable antifouling performance in the presence of external electric fields, and performed better in a 0V/2V-pulsed mode as compared with a 2V-constant mode. This in-situ combination method provides a simple and practical approach for the fabrication of composite conductive membranes, suggesting promising applications in various membrane-fabrication areas.

Water response to intense electric fields: A molecular dynamics study.

This paper investigated polarization properties of water molecules in close proximity to an ionic charge in the presence of external electric fields by using an approach based on simulations at the atomic level. We chose sodium and chloride ions in water as examples of dilute ionic solutions and used molecular dynamics simulations to systematically investigate the influence of an external static electric field on structural, dipolar, and polarization properties of water near charged ions. Results showed that a threshold electric field higher than 10(8) V/m is needed to affect water polarization and increase mean dipole moment of water molecules close to the ion. A similar threshold holds for water permittivity profiles, although a field 10× higher is needed to ensure that water permittivity is almost constant independently of the position close to the ion. Electric fields of such intensities can greatly enhance polarizability of water in hydration shells around ions.

Effect of external electric field on ground and singlet excited states of phenylalanine: A theoretical study

The effect of external electric field on the ground and few singlet excited states of phenyalanine are studied in the light of TDDFT (time dependent density functional theory) and DFRT (density functional reactivity theory). The excited state geometries are compared with the ground state ones. Sensitivity of the reactivity parameters such as total electronic energy, energy of the HOMO (highest occupied molecular orbital), global hardness (η), electrophilicity (ω) etc. towards the external electric fields are measured by varying the applied field strength. Variation of aromaticity of the ground and excited states are gauged in terms of nucleus independent chemical shift (NICS). Geometry, reactivity and aromaticity of the ground as well as excited states are responsive to the presence of external electric field.

An Alternative Approach to Solutions of the MGECSC Potential in Presence of External Electric Field

For the first time the Schrödinger equation with more general exponential cosine screened Coulomb potential in the presence of external electric field is solved approximately and analytically by applying an ansatz to eigenfunction of corresponding Hamiltonian and then energy values and wave functions are obtained. Since this potential turns into four different potential cases when considering different cases of the parameters in the potential, energies and eigenfunctions for these four different potentials are already to be found by solving Schrödinger equation with MGECSC potential. Energy values and wave functions obtained by using different values of potential parameters for each of these four different potential are compared with the results of other studies. Since the obtained general solutions in this study have been found in the presence of external electric field, the external electric field effects on systems with the mentioned four different potentials are also easily investigated. One of advantages of the present results and method is that if external electric field is equal to zero, general mathematical structure of corresponding equations does not change and then electric field effect can be eliminated. The presence or absence of electric field does not prevent solving the Schrödinger equation analytically.

The theoretical investigation of the β-crystobalite structure under the effect of electric field

In this paper, molecular dynamics simulations are carried out to study the melting process of the β-crystobalite structure under the effect of various electric fields. The results reveal that the higher electric field contributes to the damage of the β-crystobalite. Meanwhile, the applied electric field can affect the damage process of β-crystobalite, especially the melting temperature. And the melting point reduces as the strength of the electric field is increased. It is also found that the time required for the collapse of the structure strongly depends on the electric field. In addition, the presence of external electric fields results in significant changes in the electronic structures. It can be seen that there are noticeable changes in the shape of the density of states (DOS) curves.

Carbonization of aniline oligomers to electrically polarizable particles and their use in electrorheology

Abstract Aniline oligomers prepared via the oxidation of aniline under alkaline conditions at various concentrations of ammonia were carbonized at 650 °C in inert atmosphere. Subsequently, the prepared particles were mixed with silicone oil and the suspensions were used as electrorheological fluids. After the carbonization, when the higher amount of ammonia was present during the synthesis, the transition of morphology of the particles from microspheres to two-dimensional plates was observed. This transition led to a significant increase of viscosity of silicone-oil suspensions in the presence of external electric field, while their field-off viscosity remained nearly unchanged. Thus, the carbonization had the desired effect on the treated particles leading to extremely high electrorheological efficiency of the suspensions based on such particles. The highest electrorheological efficiency was achieved for the suspension based on carbonized particles prepared in 0.2 M ammonia. The dielectric spectroscopy was used as an evaluative tool of electrorheological performance of suspensions, and data correspond well with the obtained results from electrorheological experiments.

A graphene flake under external electric fields reconstructed from field-perturbed kernels

The energy, dipole moment, and polarizability of a finite hydrogen terminated zigzag graphene flake (C46H20, in 2×7 rings) are calculated in the absence of and in the presence of external electric fields reaching 5×109Vm−1 [=0.01atomic units (a.u.)]. The field intensities studied are typically found in nanoelectronics and in the tip-sample gap of a scanning tunneling microscope (STM). The change in the total energy ΔE(eV) can be closely fitted to a quadratic function of the field {1.549×104 [E (a.u.)]2} while the dipole moment μ(debye) to a linear function [2.7×E (a.u.)]. The results obtained with three different chemical models [MP2, density functional theory (B3LYP), and Hartree–Fock calculations, all with a 6-311G(2d,2p) basis set] are consistent in both trends and in absolute values. These results obtained from direct calculations are reproduced with a remarkable accuracy from a linear scaling fragmentation scheme called the kernel energy method (KEM). The KEM reproduces all studied field-free and response properties of this graphene flake model, in relative and absolute terms, independently of the underlying chemical model. An observation consistent with the known stiffness of graphene is that geometry optimization under a field as strong as 0.01a.u. insignificantly alters the total energy and the geometry of a (smaller) zigzag C28H14 flake, the difference in the field-induced stabilization energy (ΔΔE) being only 0.006eV (less than 1% of ΔE) and the average field-induced displacement of nuclear positions ∼0.0046Å [B3LYP/6-31G(d,p)].

Electric-field-modulated exchange coupling within and between magnetic clusters on metal surfaces: Mn dimers on Cu(1 1 1)

The effects of external electric fields (EFs) on the magnetic state and substrate-mediated magnetic coupling between Mn dimers on Cu(1 1 1) have been studied using a first-principles theoretical method. The calculations show that a change in the ground-state magnetic order, from antiferromagnetic (AF) to ferromagnetic (FM), can be induced within an isolated Mn2 on Cu(1 1 1) by applying a moderately strong EF of about 1 V Å−1. The magnetic exchange coupling between pairs of dimers displays Ruderman–Kittel–Kasuya–Yosida-like oscillations as a function of the interdimer distance, which depend significantly on the magnetic order within the dimers (FM or AF) and on their relative orientation on the surface. Moreover, it is observed that applying EFs allows modulation of the exchange coupling within and between the clusters as a function of the intercluster distance. At short distances, AF order within the dimers is favoured even in the presence of EFs, while for large distances the EF can induce a FM order. EFs pointing outwards and inwards with respect to the surface favour parallel and antiparallel magnetic alignment between the dimers, resspectively. The dependence of the substrate-mediated interaction on the magnetic state of Mn2 is qualitatively interpreted in terms of the differences in the scattering of spin-polarized surface electrons.

Structures and Chemical Properties of Silicene: Unlike Graphene

The discovery of graphene and its remarkable and exotic properties have aroused interest in other elements and molecules that form 2D atomic layers, such as metal chalcogenides, transition metal oxides, boron nitride, silicon, and germanium. Silicene and germanene, the Si and Ge counterparts of graphene, have interesting fundamental physical properties with potential applications in technology. For example, researchers expect that silicene will be relatively easy to incorporate within existing silicon-based electronics. In this Account, we summarize the challenges and progress in the field of silicene research. Theoretical calculations have predicted that silicene possesses graphene-like properties such as massless Dirac fermions that carry charge and the quantum spin Hall effect. Researchers are actively exploring the physical and chemical properties of silicene and tailoring it for wide variety of applications. The symmetric buckling in each of the six-membered rings of silicene differentiates it from graphene and imparts a variety of interesting properties with potential technological applications. The pseudo-Jahn-Teller (PJT) distortion breaks the symmetry and leads to the buckling in silicenes. In graphene, the two sublattice structures are equivalent, which does not allow for the opening of the band gap by an external electric field. However, in silicene where the neighboring Si atoms are displaced alternatively perpendicular to the plane, the intrinsic buckling permits a band gap opening in silicene in the presence of external electric field. Silicene's stronger spin orbit coupling than graphene has far reaching applications in spintronic devices. Because silicon prefers sp(3) hybridization over sp(2), hydrogenation is much easier in silicene. The hydrogenation of silicene to form silicane opens the band gap and increases the puckering angle. Lithiation can suppress the pseudo-Jahn-Teller distortion in silicene and hence can flatten silicene's structure while opening the band gap. So far, chemists have not successfully synthesized and characterized a free-standing silicene. But recently chemists have successfully produced silicene sheets and nanoribbons over various substrates such as silver, diboride thin films, and iridium. The supporting substrate critically controls the electronic properties of silicene, and the match of the appropriate support and its use is critical in applications of silicene.

Anomalies in radiation-collisional kinetics of Rydberg atoms induced by the effects of dynamical chaos and the double Stark resonance

Radiative and collisional constants of excited atoms contain the matrix elements of the dipole transitions and when they are blocked one can expect occurring a number of interesting phenomena in radiation-collisional kinetics. In recent astrophysical studies of IR emission spectra it was revealed a gap in the radiation emitted by Rydberg atoms (RA) with values of the principal quantum number of n≈10. Under the presence of external electric fields a rearrangement of RA emission spectra is possible to associate with manifestations of the Stark effect. The threshold for electric field ionization of RA is E≈3·104 V/cm for states with n>10. This means that the emission of RA with n≥10 is effectively blocked for such fields. In the region of lower electric field intensities the double Stark resonance (or Förster resonance) becomes a key player. On this basis it is established the fact that the static magnetic or electric fields may strongly affect the radiative constants of optical transitions in the vicinity of the Föster resonance resulting, for instance, in an order of magnitude reduction of the intensity in some lines. Then, it is shown in this work that in the atmospheres of celestial objects lifetimes of comparatively long-lived RA states and intensities of corresponding radiative transitions can be associated with the effects of dynamic chaos via collisional ionization. The Föster resonance allows us to manipulate the random walk of the Rydberg electron (RE) in the manifold of quantum levels and hence change the excitation energies of RA, which lead to anomalies in the IR spectra.

Mobility edge phenomenon in a Hubbard chain: A mean field study

We show that a tight-binding one-dimensional chain composed of interacting and non-interacting atomic sites can exhibit multiple mobility edges at different values of carrier energy in presence of external electric field. Within a mean field Hartree-Fock approximation we numerically calculate two-terminal transport by using Green's function formalism. Several cases are analyzed depending on the arrangements of interacting and non-interacting atoms in the chain. The analysis may be helpful in designing mesoscale switching devices.

Development of polaron-transformed explicitly correlated full configuration interaction method for investigation of quantum-confined Stark effect in GaAs quantum dots

The effect of external electric field on electron-hole (eh) correlation in gallium arsenide quantum dots is investigated. The electron-hole Schrodinger equation in the presence of an external electric field is solved using explicitly correlated full configuration interaction method and accurate exciton binding energy and electron-hole recombination probability are obtained. The effect of the electric field was included in the 1-particle single component basis functions by performing variational polaron transformation. The quality of the wavefunction at small inter-particle distances was improved by using Gaussian-type geminal function that depended explicitly on the electron-hole separation distance. The parameters of the explicitly correlated function were determined variationally at each field strength. The scaling of total exciton energy, exciton binding energy, and electron-hole recombination probability with respect to the strength of the electric field was investigated. It was found that a 500 kV/cm change in field strength reduces the binding energy and recombination probability by a factor of 2.6 and 166, respectively. The results show that the eh-recombination probability is affected much more strongly by the electric field than the exciton binding energy. Analysis using the polaron-transformed basis indicates that the exciton binding should asymptotically vanish in the limit of large field strength.

An interferometric study of a model of a biomembrane based on liquid crystal

A variation in the thickness of a biomembrane based on liquid crystal is experimentally studied in the presence of external electric field using a low-Q-factor Fabry-Perot interferometer. Variation in the thickness of the membrane is determined with the aid of the interference pattern of the reflected beam with an accuracy of up to 0.1 A. The nonlinear elasticity of the liquid crystal is determined from the experimental data. Chaotic fluctuations of the membrane are observed at a certain threshold voltage.

External Electric Field Effect on Electrons Transport in Carbon Nanotubes

Electronic transport properties of carbon nanotubes are studied theoretically in the presence of external electric field E(t) by using the Boltzmann's transport with constant relaxation time. An analytical expression for the current densities of the nanotubes are obtained. It is observed that the current density-electric field characteristics of the CNs exhibit total self-induced transparency and absolute negative conductivity

외부전기장 적용 섬유상 에어필터의 절연 전극 사용에 따른 여과특성

Applying an external electric field across air filter media is one of methods to improve the filtration performance. Metal wire meshes have been commonly used as electrodes situated on both sides of a thick filter pad. For a thin filter medium a short circuit, known as the biggest drawback for applying an external electric field to air filter, can occur at the closest point between electrodes. In this study several types of insulated meshes were prepared by coating #50 meshes with a dielectric material, Nylon 66, and the filtration property of air filter was evaluated at the presence of external electric field using those insulated meshes as electrodes and compared with that of filters using bared meshes. The collection efficiency of tested filter was increased from 78% to 95% for singly charged 100 nm particles by application of external electric field. As a result, there was no significant difference in collection efficiency between filters with insulated and bared electrodes. Similar results could be also seen from the tests using polydisperse particles. Finally, through this study, we found that the insulation of mesh electrodes doesn`t affect the filtration performance of fibrous air filter under external electric field.

Unidirectional Rolling Motion of Nanocars Induced by Electric Field

Understanding microscopic mechanisms of motion of artificial molecular machines is fundamentally important for scientific and technological progress. It is known that electric field might strongly influence structures and dynamic properties of molecules at the nanoscale level. Specifically, it is possible to induce conformational changes and the directional motion in many surface-bound molecules by electric field in scanning tunneling microscopy (STM) experiments. Utilizing a recently developed theoretical method to describe charge transfer phenomena for fullerenes near metal surfaces, in this work we theoretically investigated dynamics of fullerene-based nanocars in the presence of external electric field. Our approach is based on classical rigid-body molecular dynamics simulations that allow us to fully analyze dynamics of nanocars on gold surfaces. Theoretical calculations predict that it is possible to drive nonpolar nanocars unidirectionally with the help of external electric field. It is shown also that charge transfer effects play a critical role in driving nanocars and for understanding mechanisms of the directionality of the observed motion. Our theoretical predictions explain experimental observations on moving nanocars along metal surfaces.

Modification of the electric properties of molecular devices via gradual increase of number of nitrogen atoms: A computational study

This paper introduces a new means to manipulate electronic structures and, consequently, the electrical properties of molecular devices via gradual increase of number of nitrogen atoms in the backbone of conjugated organic molecular systems. Diblock molecules were selected for this purpose. Density functional theory (DFT) was used to investigate geometrical and electronic structures in the absence and presence of external electric field. Furthermore, the tendency of the anchor sulfur atoms toward electrodes in a simulated closed circuit was estimated from the relative condensed Fukui function. The obtained results indicated that HOMO–LUMO gap decreases steadily with increasing the number of nitrogen atoms, which would be used as a means for modifying the electrical properties in a regular mode.

Rotational regimes of freely suspended liquid crystal films under electric current in presence of an external electric field

The electrohydrodynamic (EHD) vortices produced by an electric current in freely suspended liquid crystal (LC) films of N-(4-methoxybenzylidene)-4-butylaniline (MBBA), convert to a pure rotation in the presence of external electric field (\(\it{E}_{{\rm ext}}\)) perpendicular to the current direction. Here, the direction and strength of the rotation are precisely under control by our self-made device called “liquid-film motor”. In this paper, we present experimental observations of the EHD fluid flow when external electric field varies from zero to a value in which pure rotation on the liquid crystal (LC) film is observed. We also show experimentally that the presence of external electric field causes a great decrease in the current produced by the voltage VJ required for observing EHD vortices in freely suspended films of MBBA. The LC films begin to rotate when EextVJ reaches a threshold value. This threshold is investigated experimentally as a function of voltage VJ and the external electrical field \(\it{E}_{{\rm ext}}\).