Plasma waves in a two-dimensional electron system laterally screened by a metallic gate

The dispersion of magnetoplasma and plasma excitations in two-dimensional electron systems, whose edges are formed by a voltage applied to a metallic gate, has been studied. A substantial decrease in the plasma wave frequency as compared to the plasma frequency measured in the etched mesas with the same geometry, size, and electron density has been observed. The dependence of the observed frequency softening on the structure size has been studied and the laterally screened plasma excitation has been shown to violate the square-root dispersion relation.     

Magnetoplasma oscillations of a two-dimensional electron system with spin-orbit interaction in a lateral superlattice

Low-frequency magnetoplasmon modes in a one-dimensional lateral superlattice with Rashba spin-orbit splitting are considered. Such modes correspond to oscillations related to virtual transitions within a Landau level that become possible due to the broadening of each Landau level into a band produced by the superlattice potential. The specificity of the one-dimensional intersubband plasmons emerging in such a system has been revealed.     

Light absorption by a two-dimensional quantum dot superlattice

The monochromatic light absorption in an ideal two-dimensional quantum dot superlattice (QDSL) is considered theoretically. Calculations of the absorption coefficient are done in both the absence and presence of a homogeneous DC electric field with rational and irrational orientations. The explicit dependencies of the absorption coefficient on the frequency of the light, the QDSL parameters and the strength of the electric field are found. Some numerical results for GaAs—Ga_0.7Al_0.3As QDSL are obtained.     

Focusing of an atomic beam by a two-dimensional magneto-optical trap

A method for focusing neutral atoms based on the light-pressure force in a nonuniform magnetic field is proposed and analyzed. Its particular scheme is realized by means of a two-dimensional magneto-optical trap using a thermal beam of Rb atoms. A feature of this focusing method is the linear dependence of the focal length on the longitudinal velocity of atoms in contrast to the quadratic dependence in the known methods of focusing material-particle beams. The minimum size of the waist of the focused atomic beam is equal to 270 μm. Owing to focusing by means of the two-dimensional magneto-optical trap, the velocity monochromatization of a thermal atomic beam is realized: the width of the distribution of the longitudinal atomic velocities in the beam is reduced from 350 to 60 m/s. Original Russian Text ? P.N. Melentiev, P.A. Borisov, S.N. Rudnev, A.E. Afanasiev, V.I. Balykin, 2006, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2006, Vol. 83, No. 1, pp. 16–20.     

Possibility of the propagation of an electromagnetic soliton in a two-dimensional superlattice

A two-dimensional electron structure in a system with a periodic potential, i.e., a two-dimensional superlattice, is investigated. An equation is derived describing the propagation of an electromagnetic wave in a two-dimensional superlattice. It is shown that an electromagnetic soliton can propagate in a two-dimensional superlattice, where it is detectable experimentally because it can induce a pulsed entrainment current. The influence of an elliptically polarized (specified) electromagnetic wave on the form of the soliton is also investigated. It is shown that a solitary wave can be amplified under certain conditions. Fiz. Tverd. Tela (St. Petersburg) 39, 1470–1472 (August 1997)     

Spectrum of an electron in a superlattice along a cylindrical quantum wire

The quasi-one-dimensional superlattice of two contacting semiconductor materials along a cylindrical quantum wire (using the example of CdS/HgS) is investigated. It is shown that the energy center of the electron is an alternation of allowed and forbidden bands. The dispersion law for different values of the period of the potential and the radius of the quantum wire is investigated. A transition to the Kronig-Penney model is obtained. The effective masses of the electrons of different bands are found. Chernovits State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 96–103, February, 1998.     

Imaging and manipulation of adatoms on an alumina surface by noncontact atomic force microscopy

Noncontact atomic force microscopy (NC-AFM) has been performed on an aluminum oxide film grown on NiAl(110) in ultrahigh vacuum (UHV) at low temperature (5 K). Results reproduce the topography of the structural model, unlike scanning tunnelling microscopy (STM) images. Equipped with this extraordinary contrast the network of extended defects, which stems from domain boundaries intersecting the film surface, can be analysed in atomic detail. The knowledge of occurring surface structures opens up the opportunity to determine adsorption sites of individual adsorbates on the alumina film. The level of difficulty for such imaging depends on the imaging characteristics of the substrate and the interaction which can be maintained above the adsorbate. Positions of single adsorbed gold atoms within the unit cell have been determined despite their easy removal at slightly higher interaction strength. Preliminary manipulation experiments indicate a pick-up process for the vanishing of the gold adatoms from the film surface.     

Quantum Hall effect in a two-dimensional electron gas with spin-orbit coupling in the field of a surface superlattice

The Hall conductance of a two-dimensional electronic system with Rashba spin-orbit coupling in the presence of an external periodic potential of a superlattice and a perpendicular magnetic field has been calculated. The calculations were performed for an electron gas with parameters typical both of a system with weak spin-orbit coupling (AlGaAs/GaAs) and a system with relatively strong Rashba coupling (InGaAs/InAs).     

非线性Kronig-Penney超晶格的二维实映射分析

通过二维实映射研究非线性Kronig-Penney超晶格中的波输运特性，数值计算得到波矢一定情况下不同非线性系数的映射图、以及非线性系数一定情况下不同波矢的映射图.非线性Kronig-Penney超晶格中的非线性，对超晶格中波函数的Bloch波矢有明显的调节作用.随着非线性系数的增大，映射图由周期函数的有限个分立点变为准周期函数的一条闭合轨道、以及有规则或无规则的点分布. 关键词： 非线性Kronig-Penney超晶格 非线性效应 二维实映射 波矢     

Conductivity of a superlattice during electron scattering by optical phonons

The conductivity is calculated for a semiconductor with a superlattice with simultaneous actions of constant (E) and varying (E_o cos t) electric fields, considered quasiclassically. It is shown that in calculating the current-voltage characteristics (CVC) at low temperatures (k_oT h _o, _o being the optical phonon frequency) and e_o = 0 it is necessary to consider electrons as both absorbing and nonabsorbing optical phonons. The frequently used approximation of constant relaxation time is valid only for k_oTh_o, when scattering by optical phonons dominantes.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 81–84, January, 1982.     

Self-alignment of Co adatoms on in atomic wires by quasi-one-dimensional electron-gas-meditated interactions

Low-density Co atoms are found to self-align on the Si(111)-(4 x 1)-In surface in the direction of In atomic wires at incommensurate adsorption sites. Indirect interaction between a pair of Co adatoms is investigated through a site distribution function of adatoms determined with scanning tunneling microscopy. In the direction of self-alignment, the potential of the mean force between two Co adatoms is long-range and oscillatory with multiple frequencies, which correlate strongly to the electronic scattering vectors of the surface-state bands at the Fermi level. We thus attribute the Co-Co interaction to that mediated by a quasi-one-dimensional electron gas confined within the In atomic wires.     

Structural instabilities of a two-dimensional Wigner crystal in a lateral superlattice

We consider the instability of a two-dimensional Wigner crystal in a short-period lateral superlattice. To find instabilities, we calculate the phonon spectrum of the electron lattice deformed by a periodic potential. We show that one of the transverse modes of the deformed electron crystal becomes soft when the electron density exceeds a critical value. This can result in a phase transition with the formation of a charge-density wave.     

Creation of atomic W state in a cavity by adiabatic passage

We propose two relatively robust schemes to generate controllable (deterministic) atomic W states of three Λ-like atoms interacting with an optical cavity and a laser beam. Losses due to atomic spontaneous emissions and to cavity decay are efficiently suppressed by employing adiabatic passage technique and appropriately designed atom-field couplings. In these schemes the three atoms traverse the cavity-mode and the laser beam and become entangled in the free space outside the cavity.