Effect of a weak magnetic field on the state of structural defects and the plasticity of ionic crystals

The aim of this work is to examine the influence of a weak (on the energy scale) magnetic field on the state of dislocations and point defects in ionic crystals. It is found that complex point defects existing in a metastable state are sensitive to a magnetic field B∼1 T. The contributions are identified, and the kinetics of various types of reactions within the structural defects and between them leading to plastification of the crystals in a magnetic field are determined. The effect of light on the sensitivity of the point defects to a magnetic field is described, and the spectral characteristics of this effect are determined. A resonant effect of the combined action of a weak constant magnetic field and a high-frequency magnetic field on the dislocation mobility is found to occur when these fields satisfy the conditions of electron paramagnetic resonance. Zh. éksp. Teor. Fiz. 115, 605–623 (February 1999)     

磁控直流辉光等离子体放电特性

本文利用单探针诊断等离子体参数来研究自行设计的磁控直流辉光等离子体实验装置的放电特性, 从而得出电子密度与气体压强、电子密度分布与磁场位型以及磁场强度等的关系. 另外, 用有限元的方法对线圈通电产生的磁场进行数值计算, 模拟出不同接线方式的两种磁场位型分布. 通过实验得出这两种不同的位型的磁场均对等离子体的状态有一定的“控制”作用, 而且这种“控制”作用与现有理论相符合.     

Temperature dependence of relaxation times in electron focusing and antidot structures made from In0.53Ga0.47As/InP heterojunctions

The magnetoresistance of antidot lattices and the magnetic field dependence of the three-terminal resistance of transverse electron focusing (TEF) devices is studied in a 2DEG in the lattice-matched In_0.53Ga_0.47As/InP heterojunction system, as a function of temperature. Ballistic effects are observed in both types of mesoscopic devices at temperatures exceeding 100 K, and are considerably more robust than Shubnikov–de Haas (SdH) oscillations. Two effects influence the decay in the amplitude of the magnetoresistance peaks in the antidot structures, and of the focusing peaks in the TEF devices: the thermal smearing of the Fermi surface, and the increase in the electron scattering time with increasing temperature due to the increase in electron–phonon scattering. We deduce the temperature dependencies of the scattering times for the different geometries.Copright 1998 Academic Press     

Formation of electron depletion layer and parallel electric field in the separatrix region of anti-parallel magnetic reconnection

It is generally accepted that during collisionless magnetic reconnection, electrons flow toward the X line in the separatrix region, and then an electron depletion layer is formed.In this paper, with two-dimensional(2 D) particle-in-cell(PIC)simulation, we investigate the characteristics of the separatrix region during magnetic reconnection.In addition to the electron depletion layer, we find that there still exists an electric field parallel to the magnetic field in the separatrix region.Because a reduced ion-to-electron mass ratio and light speed are usually used in PIC simulation models, we also change these parameters to analyze the characteristics of the separatrix region.It is found that the increase in the ion-to-electron mass ratio makes the electron depletion layer and the parallel electric field more obvious, while the influence of light speed is less pronounced.     

Evolution of the theory of a “luminous” electron

A brief survey is presented here of studies contributing to the theory of synchrotron radiation and several quantum effects which accompany the motion of electrons in a magnetic field. Equations which describe the amplitude characteristics of radial and axial oscillations of an electron moving in a nonuniform magnetic field with a weak focus are derived on the basis of the quantum theory. The characteristics of electron spin are analyzed, with oscillations in a nonuniform field (spontaneous polarization) taken into account. Depolarizing spin resonances in accumulators are interpreted in terms of the quantum theory.     

Effect of thermal smearing on the electron-phonon spectral function obtained by inversion of normal metal tunneling data

Recently Svistunov et al inverted their normal metal tunneling data to obtain the frequency (Ω) dependence of the electron-phonon spectral function α²F(Ω) of Pb (driven normal by the application of a magnetic field). Their result is in promising agreement with that obtained using the long established superconducting tunnelling technique, especially if the excess width of the peaks in their spectrum is due to thermal smearing. In this paper the effect of thermal smearing on the inverted α²F(Ω) of Pb is calculated at 1, 2, and 4 K and a new inversion formula proposed in which the effects of thermal broadening have been eliminated.     

Scanning tunneling spectroscopy in MgB2

We present scanning tunneling microscopy measurements of the surface of superconducting MgB2 with a critical temperature of 39 K. In zero magnetic field the conductance spectra can be analyzed in terms of the standard BCS theory with a smearing parameter gamma. The value of the superconducting gap is 5 meV at 4.2 K, with no experimentally significant variation across the surface of the sample. The temperature dependence of the gap follows the BCS form, fully consistent with phonon-mediated superconductivity in this novel superconductor. The application of a magnetic field induces strong pair breaking as seen in the conductance spectra in fields up to 6 T.     

Quantum transport in parallel magnetic fields: a realization of the Berry-Robnik symmetry phenomenon

We analyze the magnetoconductance of two-dimensional electron and hole gases subject to a parallel magnetic field. It is shown that, for confining potential wells which are symmetric with respect to spatial inversion, a temperature-dependent weak localization signal exists even in the presence of a magnetic field. Deviations from this symmetry lead to magnetoconductance profiles that contain information on both the geometry of the confining potential and characteristics of the disorder.     

The oscillatory galvanomagnetic size-effect in multilayered structures

Within the framework of the modified semi-classical Fuchs-Sondheimer model, we investigated theoretically the electrical resistivity of multilayered structures (MLS) consisting of alternating metallic layers (of different purity and different thicknesses) in a transverse magnetic field as functions of the ratio of the adjacent layer thicknesses and the magnetic field value. We have derived both a general formula (valid at arbitrary values of layer thicknesses) and asymptotic expressions that are valid when metallic layers are thick or thin compared with the electron mean free path. We found a non-monotonic behavior in the resistivity vs. the value of an applied magnetic field. As we demonstrated, this behavior is sensitive to the characteristics of the electron scattering in the interlayer interfaces in low magnetic fields. Moreover, the MLS resistivity oscillates in high magnetic fields with the field value (or with the layer thicknesses). The oscillation includes the harmonics that correspond both to the each layer thicknesses and the total thickness. The intensity of the oscillation is determined by the diffusive electron scattering in the interfaces, and the oscillation amplitude is proportional to the coefficient of the electron transmission through the interlayer interfaces. We have calculated numerically the resistivity in a wide range of fields and layer thicknesses at various values of the parameters of the interface and bulk electron scattering.      

Absolute negative conductivity in zig-zag carbon nanotubes in the presence of a magnetic field

The volt-ampere and gauss-ampere characteristics of zig-zag carbon nanotubes are calculated at low temperatures based on the average electron method. The characteristics obtained are analyzed as functions of the magnetic field strength. It is revealed that a constant electric field can arise spontaneously in carbon nanotubes upon application of an alternating high-frequency electric field. This effect can be due to the nonequilibrium electron subsystem of the carbon nanotubes.     

Electron distribution function and recombination coefficient in ultracold plasma in a magnetic field

The electron distribution function and diffusion coefficient in energy space have been calculated for the first time for a weakly coupled ultracold plasma in a magnetic field in the range of magnetic fields B = 100?50000 G for various temperatures. The dependence of these characteristics on the magnetic field is analyzed and the distribution function is shown to depend on the electron energy shift in a magnetic field. The position of the “bottleneck” of the distribution function has been found to be shifted toward negative energies with increasing magnetic field. The electron velocity autocorrelators as a function of the magnetic field have been calculated; their behavior suggests that the frequency of collisions between charged particles decreases significantly with increasing magnetic field. The collisional recombination coefficient α _B has been calculated in the diffusion approximation for a weakly coupled ultracold plasma in a magnetic field. An increase in magnetic field is shown to lead to a decrease in α _B and this decrease can be several orders of magnitude.     

Anharmonic effects and the infrared singularity in magnetic chains with XY symmetry

We investigate the influence of quasi spin wave interactions on the infrared singularity in magnetic chains with XY symmetry. The interactions considered contribute to a smearing of the infrared singularity only when a smearing due to the nonlinearity of the spectrum is present. The leading anharmonic corrections to the characteristic frequency and exponent of the infrared singularity are given.     

飞秒激光等离子体中电子热传导现象的数值模拟

采用相对论电磁粒子模拟程序研究了飞秒激光等离子体相互作用中产生的电流密度、电场和自生磁场的发展演化过程。介绍了电子的非局域热输运的基本特性以及激光加热过程中温度烧蚀前沿稠密等离子体子区的预热效应、临界面附近的限流效应,以及冕区的反扩散与限流效应,得到了经典Spitzer-Harm理论描述的电子热传导随自生磁场的演化情形。数值模拟表明:在线性强激光作用下,由于电子初始时刻的无规则热运动,在等离子体上激发电磁不稳定性,而不稳定性激发的强电磁场使电子束在非常短的距离内沉积能量,同时对在激光有质动力推开电子时形成的超热电子能量输运产生抑制作用。     

磁场辅助热处理金属化碳纳米管场发射性能

利用化学镀方法对多壁碳纳米管(multi-walled carbon nanotubes,MWNTs)表面金属化镀镍(MWNTs/Ni),采用丝网印刷制备MWNTs/Ni场发射阴极,并在磁场辅助下热处理所得阴极,研究磁场辅助热处理对MWNTs/Ni阴极的场发射性能的影响,经300mT磁场辅助热处理的MWNTs/Ni的场发射阴极开启场强约为0.80V·μm~(-1),场增强因子β约为16068,对单根MWNTs/Ni在磁场中的受力情况进行建模分析,实验结果表明:磁场辅助热处理有助于提高MWNTs/Ni在阴极表面的直立分布,提高了MWNTs/Ni的场发射性能。     

基于光子晶体光纤交叉敏感分离的磁场温度传感研究

提出了一种基于定向耦合效应和表面等离子共振效应的交叉敏感分离的磁场温度传感结构.在光子晶体光纤的一个特定空气孔中填充磁流体,利用磁流体的磁光效应和定向耦合效应形成磁场传感通道;在垂直方向的另一空气孔的内壁镀金纳米薄膜并填充甲苯液体,利用甲苯的温敏效应和表面等离子共振效应形成温度传感通道.对应输出谱出现两个损耗峰,测量损耗峰位置可以间接测出磁场强度和温度变化.通过理论计算()和结构优化,在90—270 Oe1 Oe=10~3/(4π) A/m范围内,磁场强度的灵敏度最高可达1.16 nm/Oe;在25—60?C范围内,温度的灵敏度可达-9.07 nm/?C.虽然填充的两种液体的折射率都受环境温度的影响,但通过建立灵敏度系数矩阵,可以消除磁场强度与温度的交叉敏感,实现磁场温度双参量的高灵敏度检测.     

高温等离子体中太赫兹波的传输特性

通过解析方法研究了高温等离子体的太赫兹波传输特性.研究发现,高温等离子体对太赫兹波高频频段透过率较高,表现为通带;对低频频段透过率较低,表现为阻带.这与冷等离子体中电磁波的传输特性是一致的.但其透射率还受到温度与磁场的影响,当改变高温等离子体的电子温度与磁场时,在阻带内会产生一尖锐的透射峰.这种现象在冷等离子体模型中从来没有出现过.本文主要对电子温度和外加磁场两个影响因素进行讨论.研究发现,禁带内出现的透射峰频率受磁场影响,而峰值幅度受温度影响.计算得到了不同外加磁场条件下产生高透过率(透射率约为1)时的电子温度.基于该结果进一步研究了透射峰出现的规律,并通过曲线拟合的方法得到了透射峰频率所遵循的计算公式.数值结果表明透射峰频率与外磁场之间为正比例函数关系,而峰值电子温度取值与外磁场的关系表现为指数规律.最后对拟合得到的方程采用时域有限差分法进行了验证,数值结果与解析解符合较好,证明了该研究的正确性.     

低速度零散会切电子枪的设计和数值仿真

根据拉格朗日方程对电子在平滑会切磁场中的径向波动与速度零散的关系进行讨论。运用Matlab,Magic软件相互结合的方法设计电子枪结构和磁场。用Matlab程序模拟单电子在给定电场、磁场中的运动,分析了单电子径向速度对零散的影响,并优化磁场分布。设计的磁场可以有效地减小单电子束径向速度,降低电子束速度零散。用Magic软件对电流为1 A、能量为30 keV的电子束在优化磁场中的运动进行仿真,得到的电子束速度比约为2,速度零散小于2.5%,轴向速度零散小于8.5%。     

Effects of Weak Localization and Electron–Electron Interaction in GaAs–AlGaAs Heterostructures

The influence of the processes of weak localization and electron–electron interaction in an inhomogeneous two-dimensional electron gas of a single GaAs–AlGaAs heterojunction on the low-temperature transport characteristics in the case of occupation of two quantum subbands has been investigated. The transport characteristics have been interpreted from the viewpoint of a two-layer model taking into account the existence of two bypass conduction channels corresponding to the two-dimensional and three-dimensional electron gas. Both the electrical and optical measurements point to the existence of large-scale fluctuations of the potential, which determine the dependence of the conduction and the Hall resistance of the heterostructures on the magnetic field. It has been established that the weak localization determines the charge transport in a weak magnetic field, and the electron–electron interaction determines this transport in a strong magnetic field.     

太赫兹波在飞行器等离子体鞘套中的传输特性

针对临近空间飞行器的黑障问题,根据模拟的RAM C-Ⅲ飞行器周围的流场分布结果,计算了等离子体电子密度和碰撞频率,并根据其分布建立了非均匀的等离子体模型。在此基础上,利用散射矩阵方法分析了太赫兹波在等离子体中的传输特性随着等离子体密度、等离子体厚度、等离子体碰撞频率的变化以及外加磁场对传输特性的影响。结果表明,太赫兹波的传输损耗随着等离子体电子密度和等离子体厚度的增加而增加,而碰撞频率的增加会使得透射率先减小后增加。在外加磁场的作用下,左旋太赫兹波的传输特性会得到改善;而对于右旋太赫兹波,磁场的施加会引入吸收峰,并且随着磁感应强度的增加向高频方向移动。     

Modeling the effect of spin polarization of magnetic moments of electrons on crossover formation

We present the results from investigations of the effect of spin polarization on crossover formation in electron microscopes. Spatial distributions of magnetic states of electrons for the electron beams in the crossover of the electron gun are analyzed by the example of a self-consistent spin-polarization field. The factors able to affect the spatial resolving ability and sensitivity of scanning microscopy are evaluated.