Increase Of External Electric Field Research Articles

Electric controlled spin and valley transport of massive electrons in graphene with spin-orbit coupling

In this work, we have explored the influence of an external electric field on the spin and valley transport of massive electrons in a graphene system with spin-orbit coupling. Both the strength and width of the spin- and valley-polarization are greatly dependent on the external electric field. As the external electric field increases, the spin/valley polarization can be enhanced, even up to 100%. In addition, the presence of a gap resulting from the interplay of massive electrons and spin-orbit coupling can occur in the direction of the spin polarization being changed. Without the gap, spin-down electrons can be filtered at the low-energy Fermi level. However, with the gap, the effect is just the opposite; spin-up electrons are filtered. These findings may open an avenue for the electric control of valley and spin transport in graphene-based electronic devices.

Polarised black holes in AdS

We consider solutions in Einstein–Maxwell theory with a negative cosmological constant that asymptote to global AdS4 with conformal boundary . At the sphere at infinity we turn on a space-dependent electrostatic potential, which does not destroy the asymptotic AdS behaviour. For simplicity we focus on the case of a dipolar electrostatic potential. We find two new geometries: (i) an AdS soliton that includes the full backreaction of the electric field on the AdS geometry; (ii) a polarised neutral black hole that is deformed by the electric field, accumulating opposite charges in each hemisphere. For both geometries we study boundary data such as the charge density and the stress tensor. For the black hole we also study the horizon charge density and area, and further verify a Smarr formula. Then we consider this system at finite temperature and compute the Gibbs free energy for both AdS soliton and black hole phases. The corresponding phase diagram generalizes the Hawking–Page phase transition. The AdS soliton dominates the low temperature phase and the black hole the high temperature phase, with a critical temperature that decreases as the external electric field increases. Finally, we consider the simple case of a free charged scalar field on with conformal coupling. For a field in the SU(N ) adjoint representation we compare the phase diagram with the above gravitational system.

Effect of Electric-Field on Spin Injection Efficiency in the Organic Semiconductors

The spin injection efficiency in the ferromagnet/ organic semiconductors system (FM/OSE) was studied under an external electric-field. It is found that the spin injection efficiency can be strongly influenced by the spin-dependent electrical conductivity and the downstream spin diffusion length of polarons. With the increase of external electric-field, the downstream spin diffusion length increases and makes the spin-dependent electrical conductivity increase, too. So the spin injection efficiency is enhanced. When the external electric-field increases from 1 to 10 mV/μm at T=80K, the spin injection efficiency increases about 20%. It seems that the downstream spin diffusion length is an significant factor to affect the spin injection efficiency in the FM/ OSE under an external electric-field.

Influence of external electric field on piezotronic effect in ZnO nanowires

In this work, the piezotronic effect is investigated for the first time in external electric fields ranging from 0 V·cm–1 to 2,000 V·cm–1 by using n-type ZnO nanowires supported by a flexible substrate. In the presence of an external electric field, the Schottky barrier height (SBH) is lowered by the image force, allowing more free carriers to pass through the metal-semiconductor junction and enhancing the screening effect on positive piezoelectric polarization charges. As the strength of the external electric field increases, the piezotronic effect is significantly suppressed and the metal-semiconductor contact finally exhibits Ohmic behavior. The experimental results show that devices can be classified into three groups, corresponding to low, moderate, and high carrier densities of the nanowires used. This work not only helps us to explicate the basic physical mechanism of the piezotronic effect in a harsh environment in an electric field but also provides guidelines for future design and fabrication of piezotronic devices.

Effects of edge magnetism and external electric field on energy gaps in multilayer graphene nanoribbons

Using first-principles density-functional theory, we study the electronic structure of multilayer graphene nanoribbons as a function of the ribbon width and the external electric field, applied perpendicular to the ribbon layers. We consider two types of edges (armchair and zigzag), each with two edge alignments (referred to as alpha- and beta-alignments). We show that, as in monolayer and bilayer armchair nanoribbons, multilayer armchair nanoribbons exhibit three classes of energy gaps which decrease with increasing width. Nonmagnetic multilayer zigzag nanoribbons have band structures that are sensitive to the edge alignments and the number of layers, indicating different magnetic properties and resulting energy gaps. We find that energy gaps can be induced in ABC-stacked ribbons with a perpendicular external electric field while in other stacking sequences, the gaps decrease or remain closed as the external electric field increases.

Temporal analysis of low-amplitude screening spatial solitons due to two-photon photorefractive effect

This paper investigates the temporal behavior of two-photon screening spatial solitons using a numerical technique. An expression for the time-dependent dynamical evolution is obtained. The results show that the width of bright solitons decreases monotonically to a minimum toward steady state value when the intensity ratio of the solitons is small, which is in low-amplitude regime. Within the same propagation time, the intensity width of solitons decreases with increase in soliton intensity ratio and with increase in external electric field. The formation time of solitons is independent of the intensity ratio of the solitons or the external electric field and is close to a constant determined by the dielectric relaxation time. The temporal properties of dark solitons are similar to those of the bright solitons.

The Stark effect in Rydberg states of a highly polar diatomic molecule: CaF

The Stark effect in molecular Rydberg states is qualitatively different from the Stark effect in atomic Rydberg states because of the anisotropy of the ion core and the existence of rotational and vibrational degrees of freedom. These uniquely molecular features cause the electric-field-induced decoupling of the Rydberg electron from the body frame to proceed in several stages in a molecule. Because the transition dipole moment among the same-n* Rydberg states is much larger than the permanent dipole moment of the ion core, the decoupling of the Rydberg electron from the ion core proceeds gradually. In the first stage, analyzed in detail in this paper, l and N are mixed by the external electric field, while N+ is conserved. In the further stages, as the external electric field increases, N+, n*, and v+ are expected to undergo mixing. We have characterized these stages in n*=13, v+=1 states of CaF. The large permanent dipole moment of CaF+ makes CaF qualitatively different from the other molecules in which the Stark effect in Rydberg states has been described (H2, Na2, Li2, NO, and H3) and makes it an ideal testbed for documenting the competition between the external and CaF+ dipole electric fields. We use the weak-field Stark effect to gain access to the lowest-N rotational levels of f, g, and h states and to assign their actual or nominal N+ quantum number. Lowest-N rotational levels provide information needed to disentangle the short-range and long-range interactions between the Rydberg electron and the ion core. We diagonalize an effective Hamiltonian matrix to determine the l-characters of the 3 < or = l < or = 5 core-nonpenetrating 2Sigma+ states and to characterize their mixing with the core-penetrating states. We conclude that the mixing of the l=4, N-N+=-4(g(-4)) state with lower-l 2Sigma+ states is stronger than documented in our previous multichannel quantum defect theory and long-range fits to zero-field spectra.

Theoretical investigations on the geometric and electronic structures of polyacetylene molecule under the influence of external electric field

The geometric and electronic structures of all-trans polyacetylene (PA) molecule in neutral, cationic, and anionic states have been studied theoretically by density functional theory method at the B3LYP/6-31+G* level. The results show that both the geometric and electronic structures of the PA molecule are sensitive to the external electric field (EF). For neu- tral PA molecule, with the increase of EF, the carbon-carbon single bonds are shortened while the carbon-carbon double bonds are elongated. The energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (LUMO-HOMO gap) decreases with the EF increasing. For cationic PA molecule, the carbon-carbon single bonds and carbon-carbon double bonds on the high potential side are elongated and shortened, respectively. While, the carbon- carbon single bonds and carbon-carbon double bonds on the low potential side are shortened and elongated, respectively. Contrary to the neutral PA case, the LUMO-HOMO gap increases with the EF increasing. Contrast to the case of cationic PA, the evolution of carbon-carbon bond lengths for the anionic PA molecule under the external EF reverses. The LUMO- HOMO gap of the anionic PA molecule decreases with the increase of external EF. In addition, the spatial distributions of the HOMO and LUMO under the influence of external EF are also discussed for the PA molecule in neutral, cationic, and anionic states.

Analysis for relationship of transmembrane potential–pulsed electric field frequency

The paper presents a model of a spherical cell. The transmembrane potential on cell membrane is obtained by solving the Laplace's equation. The frequency dependence of the transmembrane potential in pulsed electric fields is described. The value of transmembrane potential decreases as the frequency of external electric field increases. And there is a range of frequency for the value of transmembrane potential to decrease fast. It is shown that there is a strong relationship between the value of transmembrane potential and frequency components contained in the pulse. With more low-frequency components, the value of transmembrane potential is increasing and thus a better sterilization effect can be obtained. By comparing the frequency components contained in square wave pulse, exponentially decaying pulse, oscillatory pulse and their sterilization effect respectively, the analysis results about the relationship of transmembrane potential-frequency presented in this paper is validated.

Modulation of Electroosmotic Flow by Neutral Polymers

Polymer coating is widely used to modulate the fluid flow in micro- and nanometer pores and flows that are sensitive to surface properties such as electroosmotic flow. Here we report on the dissipative particle dynamics simulations of the modulation of electroosmotic flow by neutral polymers. In these coarse-grained simulations, fluid and polymers are resolved at a scale comparable to polymer size and the two-way coupling between polymer conformation and fluid flow are explicitly accounted for. The simulations indicate that, in the parameter space explored, the screening of electroosmotic flow by polymers decreases nonlinearly as the external electric field increases. Such an observation is understood by analyzing the surface coverage by polymers, height and orientation of the grafted polymers, and the two different modes of flow screening by polymer segments as a function of the external electric field. Understanding the effects and interplay of these physical processes is crucial for the rational design of polymer coating for flow control in microfluidic and nanofluidic systems.

Conformational analysis of diphenylacetylene under the influence of an external electric field

Theoretical investigation of the torsional potentials of a molecular wire, diphenylacetylene, was carried out at the B3LYP/6-311+G** level by considering the influence of the external electric field (EF). It demonstrates that many molecular features are sensitive to the EF applied. In particular, the torsional barrier increases and the LUMO-HOMO gap decreases with the increase of EF. Quantitative correlations between these features and the external EF were revealed. The current-voltage behavior corresponding to different conformers was studied as well by non-equilibrium Green's function method combined with the density functional theory. Further, the evolution of the LUMO-HOMO gap and the spatial distribution of molecular orbital were used to analyze these structure-property relationships.

Ab initio investigations of quaterthiophene molecular wire under the interaction of external electric field

A conducting molecular wire, quaterthiophene, has been investigated theoretically at ab initio Hartree–Fock levels by considering the interaction from an external electric field. When the external electric field increases, the single bonds become shorter, the double bonds become longer, and the molecular configuration tends to be more planar. All these features make the molecular wire more conjugated. The molecular electronic structure is sensitive to the electric field as well. With increasing the electric field, the HOMO–LUMO gap decreases. Moreover, the spatial distribution of LUMO moves to the high potential end, whereas HOMO to the low potential end.

Theoretical analysis and experimental study on the influence of electric double layer on thin film lubrication

A new mathematical model for thin film lubrication is established by taking into account the effect of an electric double layer. In the present paper, experiments are carried out on a self-made tester. With a composite block and a rotating disk, influence of electric double layer on thin film lubrication is studied. Two different methods are used to reconstruct the field of electric double layer so as to change its effect. One is to change the ionic concentration of lubricants by adding additives, and the other is to apply an external electric field on friction pairs. According theoretical analysis, both the methods will apparently change the electro-viscosity of the lubricant film so as to change the lubrication performances. After theoretical calculation of electro-viscosity is amended according to the experimental results, the equations of electro-viscosity are presented. The results show that the equivalent viscosity of fluid induced by the effect of electric double layer apparently increases with the decrease of thickness of the film while the lubrication film is thin enough. The effect of electro-viscosity is weakened as the thickness of the film increases. Moreover, the effect of electro-viscosity increases with the increase of external electric field at first. When the voltage reaches a certain value, the electro-viscosity begins to decrease.

Conformational analysis of oligothiophenes in the external electric field

Fully relaxed single-bond torsional potentials of oligothiophenes (nTs, n = 2, 4, 6) under the interaction of the parallel external electric field (EF) constructed by point charges have been evaluated with semi-empirical AM1 and PM3 calculations. Consistent evolutions of the torsional potential surfaces have been observed for three nTs as the EF increases. In particular, the equilibrium molecular geometries are deformed toward planar conformations, and the torsional barriers around the central C αC α′ bond are elevated. These features are sensitive to the conjugation length as expected. For the longer conjugation, the equilibrium geometries become more planar and the torsional barrier increases more rapidly. In addition, the electronic structures of nTs can be also modulated by the application of an external EF. The increase of EF leads to reduction of the energy gap between the LUMO and HOMO.

Field-Induced structure and pair distribution function of fractals

The structure transitions in cluster-cluster aggregation (CCA) and diffusion-limited aggregation (DLA) under external electric fields have been investigated by computer simulations. With the increase of external electric field, there exists a structure transition from disorder to order, i. e., the aggregates change from fractals of diffusion-limited CCA and DLA to the electrorheological chains parallel to electric field. Pair distribution shows, the system changes from local order to long-range order gradually with the external field rising.

Dimensional crossover of quantum nucleation processes in charge-density-wave phase slips

A phenomenological model for quantum phase slips of charge-density waves that takes into account the system-size effect is presented. The process of quantum nucleation leading to the phase slip changes from vortex-pair to vortex-ring creations as the external electric field increases, which is analogous to the evolution of a ripple in a rectangular water tank. The crossover field is determined by the system size. The present model describes a number of features observed in the nonohmic conductivity in ${\mathrm{TaS}}_{3}$ at low temperature.