Generation of high harmonics by an alternating electric field in superlattices based on graphene

The conductivity of a superlattice based on graphene in an alternating electric field with a vector of intensity directed along the axis of the superlattice is described. The electronic system is described in terms of the kinetic Boltzmann equation in approximation of a constant time of relaxation. Nonlinear responses to the applied harmonic field are calculated and analyzed.     

Plasma waves in a superlattice based on graphene

The law of plasma wave dispersion in an electron gas in a superlattice based on graphene on a striped substrate is studied numerically. Calculations are performed based on the quantum theory of plasma waves in the approximation of random phases with allowance for umklapp processes. The estimated plasmon frequencies for the graphene-based superlattices on striped substrates now under theoretical study is ω ≤ 10¹⁴ s^?1.     

Plasma radiation spectra in the presence of static electric and high-frequency radiation fields

Harmonics generation of high-frequency radiation in a plasma embedded in a constant electric field is investigated theoretically. It is shown that the electron directed motion due to the static electric field yields the appearance in the plasma emission spectrum of high-frequency radiation even harmonics. The conditions are established when the even harmonics generation is as effective as that of the odd ones. At variance with the odd harmonics, the even harmonics polarization plane is found to rotate with respect to that of the fundamental field. The basic dependencies concerning the rotation angle and the generation efficiency on the plasma and field parameters are established.Received: 3 May 2004, Published online: 14 September 2004PACS: 52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.) - 52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)     

Chemical surface reactions in the presence of high electric fields

Since the invention of the field ion microscope (FIM) by E. W. Muller¹ and the first mass-spectrometric analysis of field ions by Inghram and Gomer,² these tools for field ionization have been developed considerably, as described in several monographs and summarizing artilces.^3–8 Field ion mass spectrometry (FIMS) can analyze solid surfaces with extreme sensitivity. The experimental facilities enable ultimately the identification of single surface particles, which can be correlated to individual surface sites within the atomic scale of a surface. The atom-probe, which was developed by E. W. Müller,⁹ can now analyze surface particles with high precision in mass resolution.     

Effect of a constant electric field on mutual rectification in a graphene superlattice

The effect of a transverse dc electric field on two-wave mutual rectification in a graphene superlattice (GSL) is investigated. Two field orientations are considered: (i) the polarization plane is parallel to the GSL axis and (ii) the polarization plane is perpendicular to the GSL axis. In both cases, the constant field is perpendicular to the polarization plane. The current density is calculated within a one-miniband model using the Boltzmann equation in the approximation of constant relaxation time.     

Effect of a dc electric field on the high-frequency conductivity of a graphene superlattice

Longitudinal and transverse high-frequency conductivities of a graphene superlattice placed in an additional dc electric field are calculated. It is shown that in a sufficiently strong transverse field, the dependence of the longitudinal high-frequency conductivity of the superlattice on the ac field frequency changes. This effect is explained by the nonadditivity of the electronic spectrum of the investigated structure.     

Electrons and excitons in an imperfect superlattice in electric fields

We present variational calculations of excitonic states in a superlattice coupled with a wide quantum well in electric fields. The electronic states in the structure are analyzed by using both exact solutions of the one-dimensional Schrödinger equation and the simple tight-binding approximation. We demonstrate the latter method to be well applicable to calculating and designing complicated irregular superlattices. The electron spectrum can be conveniently interpreted as a result of field-induced mixing and anticrossing of electron quantized states in the enlarged quantum well with non-equidistant Stark-ladder states in the semi-infinite ideal superlattice. The electron-hole Coulomb attraction results in a relative redistribution between the extended and the localized states in the exciton. The allowance for this redistribution has a particularly strong influence upon the exciton oscillator strength and radiative lifetime.     

Autoresonance interaction of a charged particle with an electromagnetic wave in the presence of static electric and gravitational fields

The maintenance of resonance between a particle and a nonuniform, circularly polarized wave in a vacuum by a longitudinal electrostatic field is analyzed on the basis of the concept of an autoresonance regime as the motion of a charged particle along the autoresonance separatrix; the possibility in principle of autoresonance motion of a particle in a space with nonzero curvature is established: the conditions for autoresonance in a strong static gravitational field are obtained and discussed. Taganrog State Radio-Engineering University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 29–34, February, 1997.     

Effect of the topology of a graphene/SiC nanotip emitter on the formation of rings in high electric fields

The representation of the tunneling conductance G(T) of the “dirty” (with low concentrations of the same nonmagnetic impurities in the I layer) N–I–N junction (where N is a normal metal and I is an insulator) in the form of a sum of conductances of random quantum jumpers penetrating the disordered I layer is obtained in the low-temperature region. It is shown that the axis of the parameter δ = |ε₀ ? ε_F| giving the deviation of the energy of ε₀ the quasi-local electron state on the impurity in the I layer from the Fermi energy of εF the dirty N–I–N junction contains a series of bifurcation points, at the transition through each of which (in the direction of the increase in δ) the number of maxima on the temperature dependence G(T) increases by unity; i.e., a new maximum is “born” on the curve G(T). Numerical estimates are given for the characteristic parameters of dirty N–I–N junctions indicating the possibility of the experimental observation of at least the first of these maxima.     

Computer simulations of charged colloids in alternating electric fields

We briefly review recent theoretical and simulation studies of charged colloidal dispersions in alternating electric fields (AC fields). The response of single colloid to an external field can be characterized by a complex polarizability, which describes the dielectric properties of the colloid and its surrounding electrical double layer. We present computer simulation studies of single spherical colloid, using a coarse-grained mesoscale approach that accounts in full for hydrodynamic and electrostatic interactions as well as for thermal fluctuations. We investigate systematically a number of controlling parameters, such as the amplitude and frequency of the AC-fields. The results are in good agreement with recent theoretical predictions.     

The stabilization of partially-premixed jet flames in the presence of high potential electric fields

Numerous research efforts have focused on flame stabilization and emissions. Based on initial experiments, specific mechanisms resulting from DC electric fields were chosen to be investigated, namely the chemical, thermal, and ionization mechanisms. Numerical simulations were performed on premixed propane-ozone-air flames to characterize ozone effects on flame speed resulting from the formation of ozone in high potential electric fields. These results were compared against partially premixed flame experiments to observe the dominant influences within leading edge stabilization within high potential electric fields. It was found that the electromagnetic or ionization influences, serve as the dominant effect on the combustion zone.     

Scattering polarization in the presence of magnetic and electric fields

The polarization of radiation by scattering on an atom embedded in combined external quadrupole electric and uniform magnetic fields is studied theoretically. Limiting cases of scattering under Zeeman effect, and Hanle effect in weak magnetic fields are discussed. The theory is general enough to handle scattering in intermediate magnetic fields (Hanle-Zeeman effect) and for arbitrary orientation of magnetic field. The quadrupolar electric field produces asymmetric line shifts, and causes interesting level-crossing phenomena either in the absence of an ambient magnetic field, or in its presence. It is shown that the quadrupolar electric field produces an additional depolarization in the Q/I profiles and rotation of the plane of polarization in the U/I profile over and above that arising from magnetic field itself. This characteristic may have a diagnostic potential to detect steady-state and time-varying electric fields that surround radiating atoms in solar atmospheric layers.     

Reorientation of nematic liquid crystal films by alternating and static fields

In the paper the electric field induced reorientation of a nematic liquid crystal film is investigated theoretically and experimentally. Both alternating and static fields are considered.     

Multifractal analysis of the electronic states in the Fibonacci superlattice under weak electric fields

We report the effect of substitution of Cr by V and Mn in the spin- \frac12\frac{1}{2} 1 2 dimer compound Sr₃Cr₂O₈. In the pentavalent Cr site, V ion has zero effective moment, while Mn remains in the spin-1 state. For both V and Mn substitutions, the gap in the spin excitation spectra remains almost unchanged in the dilute doping regime. The low temperature Curie tail, expected to be originated from free or quasi-free magnetic ions, is found to be larger in case of V doped samples. However, inter-dimer interaction is found to be stronger in the Mn doped samples. The underlying magnetic behaviour of these doped samples is presumably related to the effect of broken dimers due to random substitutions.