External Static Electric Field Research Articles

Photoassociation of cold heteronuclear dimers in static electric fields

The formation of heteronuclear molecules in their electronic ground states from a mixture of two ultracold atomic species via a one-photon stimulated emission process is investigated. The presence of an additional external homogeneous and static electric field is shown to severely influence the induced emission process. Using the LiCs molecule as a prototype, we study the corresponding cross section and its dependence on the continuum energy, final rovibrational state, and static electric field strength. The possibility of controlling the single-photon association process via an additional static electric field is demonstrated.

Electric-field induced phase transition in a near-surface layer of a PbMg0.33Nb0.67O3-28% PbTiO3 (001) single-crystalline plate

Abstract An (001) single-crystal plate of a solid solution of PbMg1/3Nb2/3O3-28 mol.% PbTiO3 was investigated by Wide-Angle X-ray Scattering techniques at room temperature in situ under the influence of an external static electric field (field strength E up to 13 kV cm−1) applied along the [001] direction of the wafer. Structural changes attributed to a reversible phase transition between ferroelectric modifications of the solid solution in a near electrode region of about 1 mm depth are found. Part of the near-electrode layer (of about 5 vol.% at E = 4.5 kV cm−1 and about 15 vol.% at 13 kV cm−1) transforms from the initial rhombohedral structure to another one, most probably, the monoclinic Mb phase. Changes of the profile shape of X-ray rocking curves suggest possible technical use of the electric-field induced phase transition for adaptive X-ray optics.

Fréedericksz transitions in nematic liquid crystals as boundary eigenvalue problems

Fréedericksz transitions between stationary planar deformation states, induced by cover surface interactions and by static external electric or magnetic field in a flat-parallel nematic liquid crystal cell, are studied theoretically in one-dimensional approximation. There is demonstrated that for initial stages of transition, when the deviation of director field from a boundary-induced state is small, the system of Euler-Lagrange equations for free-energy functional can be linearised and the threshold external field magnitudes can be deduced from eigenvalues of differential operator of second derivative for boundary eigenvalue problems with different boundary conditions. Different combinations of electric or magnetic field, parallel or perpendicular to the nematics layer boundaries, and different boundary conditions (including both strong and weak anchoring of nematics molecules) are analysed by using the same formalism. The considerations are based on Frank theory of static deformations of nematic liquid crystals. The formulae for the threshold fields, as depending on nematics and nematics-substrate coupling parameters, are derived. There are stated possible applications of these formulae to determining material parameters by exploiting threshold field magnitudes experimentally found.

An electrode microwave discharge in a static field

The effect of an external static electric field on an electrode microwave discharge in nitrogen is investigated at pressures of 1 to 5 Torr and incident power of 20 to 170 W. It is demonstrated that the current-voltage characteristics (CVC) of the discharge with respect to direct current are nonlinear; the nonlinearity defining the CVC is the plasma layer at the surface of the discharge chamber. Qualitative agreement is obtained between the measured CVC and those calculated using the self-consistent one-dimensional quasi-static model of microwave discharge in a system of electrodes with spherical symmetry. It is demonstrated that the applied dc voltage affects only slightly the discharge characteristics; however, it enables one to control flows of charged particles to the surface of the discharge chamber.

Neutron electric dipole moment with external electric field method in lattice QCD

We discuss a possibility that the neutron electric dipole moment (NEDM) can be calculated in lattice QCD simulations in the presence of the $CP$-violating $\ensuremath{\theta}$ term. In this paper we measure the energy difference between spin-up and spin-down states of the neutron in the presence of a uniform and static external electric field. We first test this method in quenched QCD with the renormalization group improved gauge action on a ${16}^{3}\ifmmode\times\else\texttimes\fi{}32$ lattice at ${a}^{\ensuremath{-}1}\ensuremath{\simeq}2\text{ }\text{ }\mathrm{GeV}$, employing two different lattice fermion formulations, the domain-wall fermion and the clover fermion for quarks, at relatively heavy quark mass $({m}_{PS}/{m}_{V}\ensuremath{\simeq}0.85)$. We obtain nonzero values of the NEDM from calculations with both fermion formulations. We next consider some systematic uncertainties of our method for the NEDM, using ${24}^{3}\ifmmode\times\else\texttimes\fi{}32$ lattice at the same lattice spacing only with the clover fermion. We finally investigate the quark mass dependence of the NEDM and observe a nonvanishing behavior of the NEDM toward the chiral limit. We interpret this behavior as a manifestation of the pathology in the quenched approximation.

Surface spin-wave electrodynamics of an easy-axis antiferromagnet in an external electric field

The conditions are found under which quadratic magneto-optic interaction causes the formation of virtual surface magnetic TM and TE polaritons propagating along the interface between an antiferromagnet (AFM) and an ideal metal or between an AFM and an insulator in an external static electric field directed along the easy axis of the AFM. The specific features of the reflection of a bulk electromagnetic wave incident from vacuum onto the AFM surface are studied under these conditions.

Exciton Ionization, Franz−Keldysh, and Stark Effects in Carbon Nanotubes

We calculate the optical properties of carbon nanotubes in an external static electric field directed along the tube axis. We predict strong Franz-Keldysh oscillations in the first and second band-to-band absorption peaks, quadratic Stark effect of the first two excitons, and the field dependence of the bound exciton ionization rate for a wide range of tube chiralities. We find that the phonon-assisted mechanism dominates the dissociation rate in electro-optical devices due to the hot optical phonons. We predict a quadratic dependence of the Sommerfeld factor on the electric field and its increase up to 2000% at the critical field of the full exciton dissociation.

Cholesteric elastomers in external mechanical and electric fields

In our studies, we focus on the reaction of cholesteric side-chain liquid single-crystal elastomers (SCLSCEs) to static external mechanical and electric fields. By means of linearized continuum theory, different geometries are investigated: The mechanical forces are oriented in a direction either parallel or perpendicular to the axis of the cholesteric helix such that they lead to a compression or dilation of the elastomer. Whereas only a homogeneous deformation of the system is found for the parallel case, perpendicularly applied mechanical forces cause either twisting or untwisting of the cholesteric helix. This predominantly depends on the direction in which the director of the cholesteric phase is anchored at the boundaries of the elastomer, and on the sign of a material parameter that describes how deformations of the elastomer couple to the relative rotations between the elastomer and the director. It is also this material parameter that leads to an anisotropy of the mechanical reaction of the system to compression and dilation, due to the liquid crystalline order. The effect of an external electric field is studied when applied parallel to the helix axis of a perfect electric insulator. Here an instability arises at a threshold value of the field amplitude, where the latter results from a competition between the effects of the external electric field on the one hand and the influences of the boundaries of the system, the cholesteric order, and the coupling between the director and the polymer network on the other hand. The instability is either homogeneous in space in the directions perpendicular to the external electric field and includes homogeneous shearing, or, for certain values of the material parameters, there arise undulations of the elastomer and the director orientation perpendicular to the direction of the external electric field at onset. This describes a qualitatively new phenomenon not observed in cholesteric systems yet, as these undulations are due to the coupling of the director orientation to the deformations of the elastomer. Furthermore, we find that theoretically it should be possible to synthesize cholesteric and nematic SCLSCEs in which the director can be reoriented by an external electric field without macroscopically distorting the sample; the latter applies for one specific set of values for the material parameters involved. We also propose ways of experimental access to the material parameters in the general situation.

Rotatoelectricity in cholesteric side-chain liquid single crystal elastomers

We analyze the phenomenon of rotatoelectricity which is characteristic of cholesteric side-chain liquid single crystal elastomers. Using a linearized macroscopic continuum description and our previous work we show that if such a material is exposed to a static external electric field oriented parallel to the cholesteric helical axis, the director of the liquid crystalline phase will rotate around the helical axis. The material considered is assumed to be a perfect electric insulator. We propose an experiment in which the effect of rotatoelectricity should be directly observable and from which the ratio of the material parameters involved will be accessible.

Photon propagation in magnetic and electric fields with scalar/pseudoscalar couplings: A new look

We consider the minimal coupling of two photons to neutral scalar and pseudoscalar fields, as, for instance, in the case of the Higgs boson and axion, respectively. In this framework, we analyze the photon dispersion relations in the presence of static and homogeneous external magnetic and electric fields, by taking into account the contribution of the imaginary part of the scalar/pseudoscalar self-energy. We show that this contribution cannot be neglected when it is of the same order as the photon-scalar/pseudoscalar mixing term. In addition to the usual lightlike photon propagation mode, with a refraction index $n>1$, a massive mode with mass of the order of the coupled boson mass can be induced, provided that the external field is above a particular critical value. Depending on the values of the external field, photon energy, and mass of the scalar/pseudoscalar particle, the scalar/pseudoscalar width could induce a sizable rate of photon splitting in two photons due to a strong resonant phenomenon. This effect has no practical laboratory applications for the Higgs physics due to the very large critical external magnetic or electric fields involved, for a photon energy of the order of a TeV. However, it can have relevant consequences in the axion physics or in any other scenario where light neutral scalar/pseudoscalar fields have minimal coupling with two photons.

In situ transmission electron microscopy study of electric-field-induced 90° domain switching in BaTiO3 single crystals

The 90° domain switching in single crystalline BaTiO3 under an external static electric field has been investigated by in situ transmission electron microscopy using a special homemade transmission electron microscope stage. With the initial domains gradually disappearing, new domains that are 90° away from the initial ones are observed to occur with polarizations being switched to the direction of the external electric field, and domain boundaries being changed from ⟨101⟩ to ⟨1¯01⟩ in order to maintain a “head-to-tail” arrangement.

Analysis of tunable photonic crystal directional couplers

Tunable directional coupler structures based on triangular photonic crystal lattices are investigated using the finite difference time domain method. The infiltration of nematic liquid crystal materials into the coupler waveguides allows for the control of its properties through the application of external static electric fields, which reorient the nematic director. Strong dynamical shifting of the dispersion curves, along with the decoupling frequencies and the coupling coefficient, is demonstrated. Such features render this class of couplers suitable for a range of applications. The coupling lengths accomplished are quite short even when the interaction region between the two coupler branches is widened. Furthermore, operation as a channel interleaver in wavelength division multiplexing systems is explored, and it is revealed that by proper selection of the geometrical parameters a constant channel separation of 0.8nm is achieved, with an overall length of a few hundreds of microns in wide frequency ranges.

The effect of intense laser field on the photoionization cross-section and bindingenergy of shallow donor impurities in graded quantum-well wire under an electricfield

The laser-field dependence of the impurity binding energy and donor-relatedphotoionization cross-section in graded quantum-well wire under an externalstatic electric field is calculated by a variational method and in the effective massapproximation. We have shown that, in the graded quantum-well wire structures,not only the ‘dressed’ potential but also the applied direction of the externalelectric field plays a very important role in the determination of the binding energy.

In-situ X-ray investigation of a PbMg1/3Nb2/3O3-28%PbTiO3 single-crystal plate in an external electric field

A (001) single-crystal plate PbMg1/3Nb2/3O328 mol %PbTiO3 was investigated by wide-angle X-ray scattering at room temperature in situ under the influence of an external static electric field E, applied along the [001] direction of the specimen. Excluding an initial stage of the electric field processing, the induced strain s calculated from the change of interplanar spacing, exhibited a symmetrical increase with |E|, and an anhysteretic character of the s(E) dependence, during unidirectional loops of the applied electric field. Reasons for the observed s(E) behaviour are discussed.

Vortex rings in pure water under static external electric field

The reproducible development of vortex rings in pure water under the action of a static external electric field is demonstrated. The phenomenon results from the electrochemical decomposition of water. Given the low conductivity of water in the absence of electrolyte, the field-driven buildup of hydroxide ions at the anode becomes essential to the proton release, which in turn is the result of the molecular O2(g) evolution. Water recombination processes, which have protons flowing in a hydroxide background, as a key ingredient produce the phenomenon.

Stark and field-born resonances of an open square well in a static external electric field

The resonance positions, widths (inverse lifetimes), and wave functions of a square-potential well in the presence of a static electric field are calculated by using the outgoing boundary conditions. Our study concentrates on the field-born states that, unlike the well-known Stark resonances, are not associated with the field-free bound states. The effect of a lower cutoff of the static field on the field-born resonance phenomena is studied. The feasibility of experiments, where the isolated long-lived and overlapping short-lived field-born resonances can be explored, is discussed.

Electric-field-induced adiabaticity in the rovibrational motion of heteronuclear diatomic molecules

We investigate the rovibrational dynamics of heteronuclear diatomic molecules exposed to a strong external static and homogeneous electric field. We encounter in the presence of the field the effect of induced adiabatic coupling among the vibrational and hybridized rotational motions. Exact results are compared to the predictions of the adiabatic rotor approach as well as to the previously established effective rotor approximation. A detailed analysis of the impact of the electric field is performed: the hybridized and oriented rotational motion, the mixing of angular momenta, and the squeezing of the vibrational motion are observed. It is demonstrated that these effects can well be accounted for by the adiabatic rotor approximation.

Undulation versus Frederiks instability in nematic elastomers in an external electric field

We study the behaviour of a nematic side-chain elastomer under the influence of an external static electric field for a specific geometry. For this investigation, the nematic elastomer is considered to be a perfect insulator. On the basis of a macroscopic description we generalize the classical Frederiks transition in a low-molecular-weight (LMW) nematic liquid crystal to the elastomeric case. We predict, using a linear stability analysis, that the onset of the instability can be qualitatively different from the LMW case: in liquid crystalline elastomers an undulation instability can arise at onset. Whether the analogue of a Frederiks instability or an undulation instability occurs first depends on the sample thickness as well as on the material parameters. It turns out that the parameter which describes the coupling between the deformations of the elastomer and the relative rotations between the elastomer and the director field of the nematic phase is most important for the predicted response of the system. Furthermore, we find that the magnitude of the critical electric field is much higher in the elastomeric than in the low-molecular-weight case.

Illustrative direct ab initio calculations of surface Raman spectra

Illustrative ab initio calculations of Raman spectra of pyridine (Pyr) and pyridine in metal-molecule complexes with silver (Ag+-Pyr, Ag5+-Pyr) have been undertaken. The Raman spectra were computed numerically in the standard Placzek approximation with the additional feature of a static external electric field, F, perturbation to the system Hamiltonian. F was allowed to change the system equilibrium geometry and symmetry as well as the polarisability, resulting in shifted vibration frequencies and changed Raman intensities. All calculations were done on a Hartree-Fock (HF) level using the 6-31+G* or the Sadlej p-VTZ basis sets for Pyr, and the Stevens Krauss (SBKJC) VDZ ECP basis set for Ag. Raman enhancement factors over 5 orders of magnitude were obtained. The enhancement was analyzed as being due to polarization and charge transfer induced by the metal-molecule contact in the absence of F and in the presence of a strong F as due to increased polarisability derivatives along the surface normal. The use of the present method to qualitatively and quantitatively predict surface Raman spectra is discussed.

Surface plasma resonance and magneto-optical enhancement in composites containing multicore-shell structured nanoparticles

We have formulated the conditions in which dipolar surface plasma resonance is excited by light waves in composites containing nanometer-sized, $n$-fold multicore-shell structured particles (referred henceforth as ``nano-onions'') dispersed in matrices. The nano-onions have ellipsoidal shape and an arbitrary layer number $n$, which contain shell(s) (or core) of a metal having Drude type free electrons responsible for the surface plasma oscillation. By solving a quasistatic potential boundary problem in a nano-onion that is exposed to an external static electric field, we derived the effective dielectric permittivity tensor, including off-diagonal elements, for the composites, based on the Maxwell Garnett theory. The results were utilized not only to derive the resonance conditions but also to formulate the surface charge densities on the metal surfaces, from which we determined the symmetry of the dipolar surface plasmon polaritons excited in the metal shells. Calculations made on the composites containing model nano-onions of spherical shape having $n$-fold core-shell structure of sodium and a dielectric revealed the following results: (1) The surface plasmon resonance occurs at $n$ eigenfrequencies, similar to the mechanical oscillation in $n$-fold coupled oscillators; (2) at these eigenfrequencies, the composite causes resonant peaks of light extinction coefficient, and (3) the magneto-optical Kerr effect induced by a static external magnetic field is remarkably enhanced at the resonance frequencies. The magneto-optical enhancement is augmented by hypothetically reducing the dielectric loss in Na, thus increasing the quality factor $Q$ of the surface plasmon resonance. The validity limit in our calculations based on the effective medium approximation by the Maxwell Garnett theory is discussed, comparing with the calculations made by Sinzig and Quinten [Appl. Phys. A 58, 157 (1994)] based on a rigorous Mie scattering theory treatment.