External Dc Electric Field Research Articles

Vertex correction of the anisotropic magnetic impurities to the spin polarization of 2D electron gas

In terms of Kubo's formula and Green's function method, for the two-dimensional electron gas (2DEG) with Rashba spin–orbit coupling (SOC), we study the spin polarization due to the effect from magnetic impurities with anisotropic spin dependent delta type coupling to electrons when an external dc electric field in plane is applied. The vertex correction of impurities in ladder approximation is carried out in the limit of E F ≫ 1 / τ , Δ. We find that the strength of spin polarization can be significantly modified by vertex correction and the spin polarization is relevant to the anisotropy coefficient γ, but the direction of net spin polarization cannot be changed.

Polariton dynamics of a bounded weak ferromagnetic in an external DC electric field normal to the interface

With a bounded easy-plane weakly ferromagnetic crystal magnetized tangentially to its surface taken as an example, it is shown that the external DC electric field (collinear simultaneously both with the easy magnetic axis and with the normal to the interface) can lead to the formation of multiple anomalies due to the quadratic magnetooptical interaction under the conditions of propagation of a volume TM or TE wave through the interface between magnetic and nonmagnetic media.

Effective AC and DC Responses of Nonlinear Composites at Higher Concentration

For higher concentration of inclusions, an effective medium approximation (EMA) method is used to investigate the bulk effective response of weakly nonlinear composites, which are subject to the constitutive relation of electric displacement and electric field, Dα = εαE + χα|E|2E. As an example of three dimensions, under the external AC and DC electric fields Eapp = Eα(1 + sin ωt), we have derived the general effective nonlinear response of composites by the EMA method for higher concentration of spherical inclusions. Furthermore, the effective nonlinear responses at harmonics are predicted.

Self-trapping of low-energy infrared femtosecond beams in lithium niobate

In this paper we report self-trapping of subnanojoule femtosecond near-infrared beams in photonic-grade undoped bulk lithium niobate under application of an external dc electric field. We show that the phenomenon occurs thanks to the photorefractive effect induced by a weak second-harmonic component generated under large velocity mismatch. It offers a way to extend lithium niobate's photorefractive response to the near-infrared spectrum for peak intensity lower than 1 GW/cm{sup 2}, which is three orders of magnitude lower than reported in the literature.

DISSIPATIVE REGIME OF DYNAMIC LOCALIZATION IN DOUBLE QUANTUM DOT

Dissipative electron dynamics in a double quantum dot, influenced by external ac and dc electric fields, has been analyzed. It was shown that the dissipation caused by phonon environment disappears under certain relations between electric field parameters. In this case one may perform the dynamic localization and form stable electron states localized within one of the dots.

Effect of electric field during gel-layer controlled ultrafiltration of synthetic and fruit juice

Electric field enhanced ultrafiltration of pectin–sucrose mixture (synthetic juice) and mosambi ( Citrus sinensis (L.) Osbeck) fruit juice using 50,000 (MWCO) polyerthersulfon membrane is studied in a cross-flow cell. Pectin, completely rejected by the membrane, forms a gel type layer over the membrane surface. Under the application of an external dc electric field across the membrane, gel-layer formation is restricted leading to an enhancement of permeate flux. During ultrafiltration of synthetic juice, application of dc electric field (800 V/m) increases the permeate flux to almost threefold compared to that with zero electric field. A theoretical model based on integral method assuming suitable concentration profile in the boundary layer is developed. The proposed model is used to predict the permeate flux in gel-layer governed electric field enhanced ultrafiltration. Predictions of the model are successfully compared with the experimental results under a wide range of operating conditions. Experiments with fruit juice also demonstrated significant increase in flux with the application of a suitable electric field.

Improvement of microchannel geometry subject to electrokinesis and dielectrophoresis using numerical simulations

This paper addresses the effects of microchannel geometry with electrically insulating posts on a particle flow driven by electrokinesis and dielectrophoresis. An in-house numerical program is developed using a numerical model proposed in literature to predict particle flows in a microchannel with a circular post array. The numerical program is validated by comparing the results of the present study to those in the literature. Results obtained from a Monte-Carlo simulation confirm the three particle flow types driven by an external DC electric field: electrokinetic flow, streaming dielectrophoretic flow, and trapping dielectrophoretic flow. In addition, we study the effects of electrokinetic and dielectrophoretic forces on particle transports by introducing a ratio of lateral to longitudinal forces exerted on a particle. As a result, we propose an improved microchannel geometry to enhance particle transports across electrokinetic streamlines for a given power dissipation. The improved microchannel has a shorter longitudinal spacing between the circular posts than a reference microchannel. We also discuss the critical values of dimensionless variables that distinguish the three particle flow types for both improved and reference microchannels.

Influence of shape and electric field on electron relaxation and coherent response inquantum-dot molecules

We studied the effects of the confinement geometry and of external electric field on theelectron dynamics of spherical and cylindrical double quantum dots. With an effective-massapproach, we found eigenenergies and envelope wave functions for finite confinementnumerically. Using these energy states, we studied the response of the system to electricfield pulses of different intensities, by calculating the density-matrix evolution in thehigh-delocalization regime, considering electron–electron and electron–acoustic phononinteractions, as a function of external DC electric field in the coupling direction. Weobtained suitable conditions for coherent emission from cylindrically shaped dots, while inthe case of spherically shaped dots, the scattering process is faster than the quantum beatoscillation.

Transformation of the spectra of surface magnetic TE polaritons at the quadratic electro-optic effect

The anomalies in the spectrum of surface magnetic TE polaritons at the interface between an easy-axis antiferromagnet and vacuum in an external dc electric field directed perpendicularly to the easy-magnetization axis have been studied with allowance for the quadratic magneto-optic interaction.

Single-photon double ionization of negative hydrogen ions in the presence of a dc electric field

We present an accurate numerical study of the influence an the external dc electric field on the process of single-photon double ionization of the negative hydrogen ion at photon energies from the threshold to $30\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. We demonstrate that the presence of an external dc electric field of the order of $0.005\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ may considerably alter the cross section of the process.

Retardation of grain growth in electrodeposited Cu by an electric field

The application of an external dc electric field E = 5 kV/cm during the annealing of electrodeposited Cu foil at 150–195 °C retarded grain growth. The time dependence of the grain size both with and without the field was $$D=A_{\rm o} \exp (-Q/RT)t^n$$ where A o = (3.53–4.35) × 10−5 m s−1, Q = 11.3–11.6 kJ/mole and n = 0.048–0.052. The field consistently reduced A o, but had no clear effect on Q and n. Consideration of the grain growth kinetics in terms of the expression dD/dt = M o exp (−Q M/RT)P q gave Q M = Q/n = 233–239 kJ/mole and q = 1/n−1 = 19.1–20.1. Theoretical considerations along with data in the literature on grain boundary migration in Al and Cu suggest that these values of q and Q M could reflect the action of impurities. Several possibilities are given for the decrease in A o and the corresponding retardation of grain growth by the field. Good accord occurred for a reduction by the field of the dislocation density contribution to the driving force P. Grain growth data in the literature, along with the present results, are in some accord with both the impurity drag and topology models; hence both should be considered in any analysis of grain growth kinetics.

Influence of anchoring at a nematic cell surface on threshold spatially periodic reorientation of a director

We have analysed the influence of surface director anchoring in a planar flexoelectric nematic cell on the threshold spatially periodic reorientation of the director in an external dc electric field. By minimizing the free energy of the nematic cell we obtained the equations for a director and numerically solved them in the one elastic constant approximation. The dependences of the threshold electric field and the spatial period of director structure on the azimuthal and polar anchoring energy, as well as the flexoelectric parameters, are determined. It is shown that the domain of the flexoelectric parameter values, at which the spatially periodic reorientation of a director takes place, increases with decreasing azimuthal anchoring energy and increasing polar anchoring energy.

Two-dimensional electron system with spin-orbit interaction in ac magnetic field

The response of a two-dimensional (2D) electron system with spin-orbit interaction to a dc measurement electric field has been investigated in the case when the system is driven out of equilibrium by a magnetic ultrahigh-frequency field that leads to ``combined'' transitions that involve both the translational degrees of electron freedom and its spin. For such transitions to be possible, the effects of Landau quantization and spin-orbit interaction are needed. The combined transitions modify electron scattering processes in an external dc electric field and thus lead to oscillations of the diagonal components of the conductivity tensor in high-mobility samples with a 2D electron gas.

Transformation of the polariton spectrum of a one-dimensional magnetic photonic crystal in an external dc electric field

The conditions are determined for a one-dimensional magnetic superlattice composed of an easy-axis antiferromagnet and a nonmagnetic dielectric, whose axis is collinear with the easy magnetization axis, under which quadratic magneto-optical interaction in an external dc electric field leads to a number of specific features upon localization and propagation of magnetic TM and TE polaritons.

Coupling effects on electron‐phonon scattering in double quantum dots

AbstractIn this work we study the electron‐phonon interaction in GaAs/AlGaAs double‐dot systems for cylindrical and spherical geometries with finite confinement, coupled by a tunnelling barrier and an external dc electric field. The eigenenenergies and envelope wave functions are numerically obtained for different values of the external bias. We study the effects of field and the dots‐shape on the relaxation rates of electronic transitions between double‐dot states by electron‐acoustic phonon and electron‐optical phonon interaction. We found the piezoelectric interaction to be small compared with the deformation potential one, and the spherical more convenient than the cylindrical geometry to reduce the electron‐phonon decay rates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrically controlled transfer of spin angular momentum of light in an optically active medium

Spin is an intrinsic property of the photon. A method for using an externally applied dc electric field to manipulate the transfer of spin angular momentum of light in an optically active medium is presented. To discuss this, we first develop a wave coupling theory of the mutual action of natural optical activity and the linear electro-optic effect. Besides being used for analyzing the electrically controlled transfer of spin angular momentum of light, the theory can also be used to describe the propagation of light traveling along an arbitrary direction in any optically active medium with an external dc electric field along an arbitrary direction.

Electron assisted charge transfer in superprotonic conductor K3H(SO4)2

Charge transfer of polycrystallines and mononocrystals of K3H(SO4)2 superprotonic conductor was investigated. We have shown that in an external dc electric field the protonic charge transport assisted by electrons behaves nonlinearly below the temperature of fast proton phase transition. This can be considered as a soliton-like behaviour. The current fluctuations, which are proportional to the basic current, are most probably evoked by the formation of charge density waves which are pinned/depinned in the crystal lattice. ac investigations also indicate nonlinear character of conductivity.

Single-photon double ionization of helium in the presence of dc electric field

We study the influence of the external dc electric field on the process of single-photon double ionization of helium at photon energies of 85 and $90\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Calculation is based on a numerical solution of the time-dependent Schr\"odinger equation and subsequent projection of the solution on a final state furnished by the convergent close coupling expansion. We find that for the range of the field strengths studied $({F}_{\mathrm{dc}}\ensuremath{\leqslant}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.})$ the presence of the external dc field leads to a monotonous decrease of the total probability of single-photon double electron ionization. This decrease is achieved primarily due to decreasing probability to detect electrons with unequal energy sharing.

Ferroelectric switching of electrically commanded alignment layers for liquid crystal displays

Optical second harmonic generation (SHG) was used to probe the structural and dynamic properties of electrically commanded alignment layers for liquid crystal displays. The layers were 200nm thick and were made of siloxane-based side chain ferroelectric liquid crystal polymer (FLCP). The effect of an external dc electric field in the range of 0–2V∕μm on the SHG signal was probed in an empty sandwich cell and in a cell filled with an isotropic liquid (hexadecane). In both cases the nonlinear induced polarization shows characteristics of the “V-shaped” switching, which is associated with a relatively minor reorientational perturbation of the film. This signifies a presence of domain structure, which is strongly pinned to the substrates. The values of switching times deduced from the SHG response are two orders of magnitude larger from the values obtained by optical birefringence measurements. This observation suggests that in the top surface layer of the FLCP, which is mainly responsible for the birefringence and also for the so-called electrically commanded surface effect, the reorientation of the polymer side chains takes place much faster than in the regions close to the substrate.

Generalized wave coupling theory of linear electro-optic effect in absorbent medium

Starting from Maxwell’s equations and considering the linear electro-optic effect as a perturbation, we present a generalized wave coupling theory of linear electro-optic effect in absorbent medium. We give the rigorous solution of the resultant equations for a light wave propagating along any direction with an external dc electric field along an arbitrary direction. As an application, we use the theory to discuss the influence of absorption on the light wave in a KTP crystal. The results demonstrate that the absorption coefficients influence not only the amplitude but also the phase of the light wave.