Characteristics of transmission of electrons in a quantum wire tangentially attached to a superconductor ring threaded by magnetic flux

We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve symmetry of Schr?dinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure can be well understood. Received 6 November 2001     

Magnetic Manipulation of Massless Dirac Fermions in Graphene Quantum Dot

We have theoretically analyzed the quasibound states in a graphene quantum dot (GQD) with a magnetic flux Φ in the centre. It is shown that the two-fold time reversal degeneracy is broken and the quasibound states of GQD with positive/negative angular momentum shifted upwards /downwards with increasing the magnetic flux. The variation of the quasibound energy depends linearly on the magnetic flux, which is quite different from theparabolic relationship for Schrödinger electrons. The GQD's quasibound states spectrum shows an obvious Aharonov-Bohm (AB) oscillations with the magnetic flux. It is also shown that the quasibound state with energy equal to the barrier height becomes a bound state completely confined in GQD.     

Aharonov-Bohm effect for plasmons in a finite-width quantum ring

The magnetoplasma oscillation frequencies of the 2D electrons in a quantum ring have been found taking into account the finite width of the ring in the model allowing for an exact solution for the single-particle spectrum. It is shown that instead of the periodic oscillations of the plasmon frequency ω typical of the 1D ring, ω in the case under consideration depends on the magnetic flux with the frequency and amplitude modulations: the period of oscillations as a function of the magnetic flux and their amplitude depend on the magnetic field strength.     

Electron kinetics in radio-frequency atmospheric-pressure microplasmas

The kinetic study of three radio-frequency atmospheric-pressure helium microdischarges indicates that the electron energy probability function is far from equilibrium, and three electron groups with three distinct temperatures are identified. The relative population of electrons in different energy regions is strongly time modulated and differs significantly from values recently reported from fluid analyses. It is also shown that a flux of energetic electrons (epsilon>5 eV) that comprises up to 50% of the total electron flux can reach the electrodes. This energetic electron flux provides a new means of delivering energy to the electrodes and tuning the surface chemistry in atmospheric-pressure discharges. The three electron groups and the engineering of an energetic electron flux might open up a new paradigm in plasma-surface chemistry that has not been considered up until now.     

Kinetic electron reflection coefficient in a low-voltage Knudsen arc

The influence of the escape of fast plasma electrons on the electron distribution function (EDF) in a low-voltage cesium Knudsen arc is discussed. It is shown that even with a large Knudsen parameter l _e /h∼5–10 (where h is the gap and l _e is the mean free path of electrons with energy of the order of the anode barrier) the electron flux from the plasma to the anode is virtually identical to that calculated with a Maxwellian EDF. Zh. Tekh. Fiz. 68, 61–64 (May 1998)     

Electronic energy levels of nanorings with impurities and Aharonov–Bohm effects

By modeling impurities along a nanoring as general potential forms the Schrödinger equation for ballistic electrons is shown to separate in cylindrical coordinates. We find an analytical eigenvalue equation for N delta-function-barrier impurities in the presence of magnetic flux. Previous calculations of the electronic states of a one-dimensional (1D) and two-dimensional (2D) nanoring for only one or two impurities modeled by equal square barriers is explicitly extended to three and four different or equal impurities modeled as delta-barrier, square-barrier, or delta-well potential forms. This is shown to be generalizable to any number N. Effects on the energy spectra due to magnetic flux and different kinds and numbers of impurities are compared in 1D and 2D nanorings.     

Magnetoplasma resonance in a GaAs/AlGaAs quantum well in a strong parallel magnetic field

The dispersion of magnetoplasma excitations in two-dimensional electron systems in a strong parallel magnetic field has been studied. A considerable increase in the electron cyclotron mass with an increase in the parallel component of magnetic field has been detected. It has been found that the cyclotron mass increment is a quadratic function of the magnetic field parallel to the interface. It has been shown that the mass anisotropy of 2D electrons induced by the parallel magnetic field reaches nearly 2.5 in B _‖ = 7 T. The energy of space quantization of the electron in the quantum well has been estimated from the magnetic field dependence of the anisotropy.     

Flux-dependent tunnel magnetoresistance in parallel-coupled double quantum dots

The tunnel magnetoresistance (TMR) in an Aharonov–Bohm interferometer with two quantum dots inserted in its arms, which is attached to ferromagnetic leads with parallel and antiparallel magnetic configurations, is theoretically studied by means of the nonequilibrium Green’s function technique. We pay particular attention to the influence of an applied magnetic flux on the characteristics of the TMR. In the linear response regime (the external bias voltage V→0) and when the electrons are free from intradot Coulomb interaction, the magnetic flux only changes the peak or dip positions of the TMR. But in the presence of intradot Coulomb repulsion, its peak or dip positions, signs and magnitude are tuned by the magnetic flux. For the nonlinear response regime (V≠0), the TMR is symmetric with respect to zero bias voltage and the magnetic flux can influence its magnitude, signs and the peak positions regardless of the existence of intradot Coulomb interaction. The behavior of the TMR is interpreted in terms of the quantum interference (Fano) effect.     

不同磁路下微型ECR中和器电子引出的模拟研究

电子回旋共振(ECR)中和器是微型ECR离子推力器的重要组成部分,其引出的电子用于中和ECR离子源的离子束流,避免了航天器表面电荷堆积,并且电子引出性能对推力器的整体性能起着重要作用.为了分析影响微型ECR中和器电子引出的因素,本文建立了二维轴对称PIC/MCC计算模型,通过数值模拟研究不同磁路结构对中和器的电子引出,及不同腔体长度对壁面电流损失的影响.计算结果表明, ECR区位置和引出孔附近磁场构型对中和器的电子引出性能至关重要.当ECR区位于天线上游,电子在迁移扩散中易损失,并且电子跨过引出孔前电势阱所需的能量更高.如果更多磁力线平行通过引出孔,中和器引出相同电子电流所需电压较小.当ECR区被天线切割或位于下游时,电子更易沿磁力线迁移到引出孔附近,从而降低了收集板电压.研究了同一磁路结构下不同腔体长度对电子引出的影响,发现增加腔体长度,使得更多平行轴线的磁力线通过引出孔从而避免电子损失在引出板表面,增加了引出电子电流.研究结果有助于设计合理的中和器磁路和腔体尺寸.     

Upshifted electron cyclotron emission

The possibility of inferring the high energy part of the electron distribution function by means of its electron cyclotron emission is investigated. It is shown, with different set-ups, that the emission leaving the plasma perpendicular to the magnetic field cannot achieve this goal. A new configuration viewing the plasma from the low field side, oblique respect to the magnetic field -upshifted emission — is presented and its useful properties for localizing the electrons, responsible for the emission, in real and momentum space discussed.     

Dependence of the temperature of stochastically heated electrons on the flux density of pulsed laser radiation on a target

Electron dynamics in the field of focused picosecond multimode laser radiation was considered by numerical methods. It was found that the electron energy during stochastic perturbation of its trajectory can exceed the energy of oscillatory motion in a plane wave by several orders of magnitude. The electron distribution function was studied based on 2D numerical simulation. An analytical expression for the distribution function of relativistic electrons as ideal gas was derived. The distribution function in the radiation flux density range of 10¹⁴–10¹⁷ W/cm² was compared with an analytical expression of the equilibrium distribution; a temperature characteristic for electrons stochastically heated by the laser field was introduced. The dependence of the electron temperature on the radiation flux density was determined.     

Heat-transfer mechanisms in solar flares. 1: Classical and anomalous heat conduction

In the context of the problem of energy transport in solar flares, simplified analytical models have been developed that describe plasma heating in the solar atmosphere by heat fluxes from the super-hot (T _e ≳ 10⁸ K) reconnecting current layer. It is shown that the applicability conditions of common heat conduction produced by Coulomb collisions of electrons in plasma are not fulfilled in solar flares. The heat flux calculated using the classical Fourier’s law proves to be significantly higher than the real energy fluxes known from modern multi-wavelength observations of flares. The so called anomalous flux produced by interaction of free electrons with ion acoustic waves in a plasma is critically analyzed. The question of what the dominant mechanism of heat transfer in solar flares is requires additional consideration [1].     

Effect of spontaneous magnetic fields on energy transfer by fast electrons in spherical laser targets

It is shown that the spontaneous magnetic fields generated due to development of hydrodynamic instability in the process of compression of spherical laser targets can substantially affect the energy transfer by fast electrons. The analytical solutions to the kinetic equation for the distribution function of fast electrons are obtained taking into account the reflection from the region of the magnetic-field localization. On the basis of these solutions, the effect of the spontaneous magnetic fields on the specific energy released by the fast electrons per unit mass and on preheating of the target material being compressed is investigated.     

铁磁/半导体/铁磁结构的双量子环自旋输运的特性

研究了与铁磁/半导体/铁磁结构相关的双量子环自旋输运的规律,研究结果表明：总磁通为零条件下,铁磁电极磁化方向反平行时,双量子环与单量子环相比提高了自旋电子透射概率的平均值.铁磁电极磁化方向平行时,双量子环对提高自旋向下电子平均透射概率的效果更明显;双量子环受到Rashba自旋轨道耦合作用影响时,自旋电子的平均透射概率明显高于单量子环,即使再加上外加磁场的影响,透射概率较高这一特征依然存在;双量子环所含的δ势垒具有阻碍自旋电子输运的作用,随δ势垒强度Z的增大透射概率 关键词： 双量子环 Rashba自旋轨道耦合 透射概率 δ势垒')" href="#">δ势垒     

Formation of the 255-keV annihilation line near the magnetic poles of pulsars

The possibility of existance is discussed for pulsars emitting soft γ radiation near their magnetic poles upon the annihilation of ultrarelativistic positrons from the magnetosphere and electrons from the surface of a star. With an increase in the energy of incident positrons, the photon energy of this backward radiation tends to a constant value m _e c ²/2=255 keV. This radiation is shown to be directed opposite to the positron flux direction.

     

AB效应对自旋多端输运的影响

利用紧束缚近似和格林函数方法,研究了AB效应和AB环对电子自旋输运的影响.计算表明,当在AB环的不同位置上连接相同或不同属性的输出端时,在一些能量范围内,由不同的输出端所输出的自旋流的方向是相反的;当固定入射电子的能量时,在同一磁通范围,从两个输出端输出的自旋流属性也是相反的.从而,可以通过控制AB环的结构和环内的磁通在输出端得到不同属性的自旋流. 关键词： 自旋极化输运 量子点 极化率 自旋流     

Magneto-optics of strongly correlated two-dimensional electrons in single heterojunctions

Investigations of two-dimensional (2D) electron systems in semiconductors subjected to a strong perpendicular magnetic field with the use of photoluminescence are reviewed. The foundation of the optical spectroscopy method using the radiative recombination of 2D electrons with photoexcited holes bound to acceptors in a δ-doped monolayer in GaAs/Al _x Ga_1-x As single heterojunctions is presented. Optical spectroscopy studies of the energy spectra of 2D electrons imposed on transverse magnetic fields in the regimes of the integer and fractional quantum Hall effects are discussed. The relationship between the mean energy of the 2D electron gas and the first moment of their radiative recombination is analysed. It is shown that the magnetic field dependence of the first moment provides a method to measure the cyclotron, enhanced spin and quasiparticle energy gaps at the same time. Therefore it is shown how magneto-optics ‘see’ the ground state of interacting 2D electrons in the extreme quantum limit and how an optical ‘tool’ is efficient for the determination of Coulomb gaps of incompressible Fermi fluids in the fractional quantum Hall effect. Finally optical observations and studies of the Wigner crystallization of 2D electrons are presented. The corresponding liquid-solid phase diagram is discussed.     

电子辐照能量对Kapton/Al热控涂层光学性能的影响

 研究了电子辐照时，电子能量与累积通量对Kapton/Al热控涂层光学性能的影响。采用原位测量的手段记录了辐照前后的光谱反射系数。试验结果表明，电子辐照后Kapton/Al热控涂层的反射性能,在太阳光谱辐射强度较大的300~1 200nm波长区间产生较大程度退化。在电子辐照作用下，作为离子导电型聚合物的 Kapton薄膜表面没有发现辐照充电效应。辐照后涂层材料存在“退火效应”，或称“漂白效应”。Kapton/Al涂层太阳吸收比的变化量与电子辐照累积通量的变化关系成幂函数形式,其系数与指数的极大值与极小值分别出现在电子能量为50keV附近。在辐照累积通量相同时，该变化量随辐照电子能量的提高而增大。     

On relaxation of the electron distribution function in resonant striation-like fields

Relaxation of an approximately δ-shaped distribution function of electrons injected into P and R striation-like fields on one of the resonant trajectories is analyzed. It is shown that as a result of energy diffusion, electrons appear on other resonant trajectories after several periods. Ultimately, a steady state corresponding to the distribution function in the P and R strata is formed as a result of compression to resonant trajectories and energy diffusion.     

A Mathematical Representation of Quantizing the Motion of Relativistic Electrons in a Magnetic Field

It is shown that the quadratic component of the kinetic energy of continuous longitudinal motion of relativistic electrons in the external magnetic field is varied continuously between 0 and 2(2m _e c ²_B H) within each Landau energy level, undergoing an abrupt change at the boundaries of the levels. This results in the fact that in the quantum limit of a superstrong magnetic field where all electrons are at the zero Landau level, the maximum quadratic component of the kinetic energy of free longitudinal electron motion along the direction of the magnetic field is twice as high as the maximum quadratic component of the kinetic energy of its bound transverse motion.