自旋极化电子与Xe原子的弹性碰撞

在电子与无自旋原子的弹性过程中,可认为电子是在一个向心的有效势V(r)中作相对论运动。由Slater定域近似下的相对论自洽场方法(SCF)求得该有效势。在求得有效势的基础上,采用相对论分波法,计算了极化电子与无自旋原子弹性碰撞的散射振幅,进而计算了微分截面和散射电子自旋极化参量。通过与有关的完全实验比较,明确了本文所采用理论方法的适用范围,即在E≥100eV的能量范围内,本文所用理论方法可较好地描述极化电子与无自旋原子的弹性碰撞过程。 关键词：     

类氦离子的电子碰撞电离微分截面

本文主要利用扭曲波玻恩交换近似方法(DBE)计算类氦离子在电子碰撞下,相应不同的末态电子能量分配的电离截面(能量微分截面)。发现对这些微分截面在不同靶电荷及入射能量下,都可用带两个参数的高斯函数αexp(β(x—0.5)²)很好地拟合。还给出两个拟合参数随靶电荷和入射能量的变化曲线,以及讨论了在库仑波玻恩交换近似(CBE)和DBE两种不同近似下所得参数值的差别。计算结果也表阴,在低靶电荷和低入射能量时用DBE计算的必要性。 关键词：     

Magnetic and orbital dichroism in (e,2e) ionization of sodium

We present the first measurement of (e,2e) ionization cross sections for a laser oriented atomic target by spin polarized electrons. Cross sections are presented as a function of target orientation and polarization direction of the incident electron beam. This study provides insight into mechanisms by which angular momentum is transferred from the valence electron to the two final-state continuum electrons in both singlet and triplet spin channels, by comparing measurement with distorted wave Born approximation and the dynamically screened three Coulomb wave calculations.     

一种考虑几何屏蔽效应的计算“电子-分子”散射总截面的可加性规则修正方法

在考虑分子内原子间的几何屏蔽效应随电子入射能量变化的基础上, 提出了一种能够在中、高能区准确计算“电子-分子”散射总截面的可加性规则修正方法. 利用这一修正后的可加性规则并使用“电子-C, H, O, N原子”散射总截面的实验数据, 在50—5000 eV内计算了电子被NO, N₂O, NO₂和C₂H₆分子散射的总截面, 且将计算结果与实验结果及其他理论结果进行了比较. 结果表明, 利用这一方法修正过的可加性规则进行计 关键词： 电子散射 可加性规则 总截面 几何屏蔽效应     

Elastic scattering of electrons by benzene

Relative differential cross-sections for the elastic scattering of electrons from benzene have been measured at incident energies 300, 500, 700 and 900eV and for scattering angles between 30° and 120°. The results are discussed and compared with the independent atom model (IAM) calculations. Two different sets of scattering amplitudes for the constituent atoms of benzene were used in these calculations, one obtained from first Born approximation and the other from partial wave analysis of the Dirac equation. Only the static interaction was taken into account in the calculations. The higher the incident energy, the better is the observed agreement between experiment and theory. This indicates that at higher energies, absorption, exchange and polarization effects are not significant as compared to the static interaction and that the IAM satisfactorily predicts the interference of scattering from the individual atoms of C₆H₆.     

High-energy electron pair production on oxygen

Electron-positron pair production cross sections are calculated for 50-MeV electrons incident on an oxygen nucleus. The symmetric coplanar cross sections are emphasized. Neglecting exchange, the spectra of forward-scattered projectile electrons is numerically calculated. In the extreme relativistic and nonrelativistic limits for the produced pair kinetic energies, calculated cross sections are similar to those of Bhabha.     

Inner-shell ionization of atoms by electron,positron and photon impacts

Plane wave Born approximation with Coulomb, relativistic and exchange corrections is employed to obtain L1-, L2- and L3-subshell ionization cross sections of several atoms due to electron and positron impacts for projectile energy varying from the threshold of ionization to 60 times the threshold energy. Photoionization cross sections for all the three L-subshells of the atoms are also calculated using the hydrogenic approximation for the atomic wave functions. For L3-subshell the present cross sections due to electron impact are in good agreement with a number of experimental data for different atoms over the entire energy range investigated. For L1- and L2-subshells the present calculations yield qualitative agreement with the experimental data. The agreement between the present results and the limited experimental data for positron impact is also satisfactory. The hydrogenic approximation for the L-subshell photoionization is found to be good at small photon energies but it underestimates the cross sections at large photon energies.     

电子的相对论平均场理论与一阶、二阶Rashba效应

用多体平均场意义下电子的Dirac方程讨论了电子自旋动力学及其相关问题. 在大分量Dirac方程的非相对论展开中讨论了电子自旋动力学的高阶效应,并且在二维情形下得到了包括一阶和二阶Rashba效应的电子自旋动力学哈密顿量,求出了相应的包括二阶Rashba效应的哈密顿量的能量和波函数的本征值解,由此讨论了二阶Rashba效应修正的物理含义和大小. 关键词： 二阶Rashba效应 自旋电子学 Dirac方程 相对论平均场理论     

低能质子引起的金LX射线相对产生截面

对于能量为０．５－１ＭｅＶ的入射质子，在计算中采用ＡｕＬ１次壳层荧光产额的实验值代替相应的Ｄｉｒａｃ－Ｈａｒｔｒｅｅ－Ｓｌａｔｅｒ值时，使用ＲＰＷＢＡ－ＢＣ（经结合能和库仑歪曲修正的相对论平面波玻恩近似）电离截面计算得到的金原子ＬＸ射线相对产生截面与测量值相符。以前报道的对ＲＰＷＢＡ－ＢＣ截面的各种修正都是不需要的     

SiC单层内Co空间选位对自旋组态的调控

基于第一性原理的密度泛函理论,对SiC单层不同位置掺杂Co进行了能带结构、电子态密度、净自旋密度和自旋纹理等计算,结果表明不同位置的掺杂引起不同特征的自旋积累及单层的电子结构特性。由于Co的不同选位掺杂而产生一些新奇现象,如扭曲的Co-C键在掺杂SiC内激发了自旋流而诱导了自旋重新分布,不同选位的Co原子通过调整内磁场改变了小极化子内巡游电子的定域属性,增加了Dirac点附近磁振子的色散强度等。这些研究结果为得到一个人工调控量子自旋电路和选频自旋波器件内自旋谷电子提供了理想平台。     

Reversal of Klein reflection by magnetic barriers in bilayer graphene

Massless Dirac fermions in monolayer graphene exhibit total transmission when normally incident on a scalar potential barrier, a consequence of the Klein paradox originally predicted by O Klein for relativistic electrons obeying the 3 + 1 dimensional Dirac equation. For bilayer graphene, charge carriers are massive Dirac fermions and, due to different chiralities, electron and hole states are not coupled to each other. Therefore, the wavefunction of an incident particle decays inside a barrier as for the non-relativistic Schr?dinger equation. This leads to exponentially small transmission upon normal incidence. We show that, in the presence of magnetic barriers, such massive Dirac fermions can have transmission even at normal incidence. The general consequences of this behavior for multilayer graphene consisting of massless and massive modes are mentioned. We also briefly discuss the effect of a bias voltage on such magnetotransport.     

Na原子及类Na离子Fe15+价壳层光电离过程的理论研究

采用相对论多组态Dirac-Fock理论,计算了Na原子及类Na离子Fe15++基态的光电离截面.对Na原子,考虑相对论效应与弛豫效应,本文计算结果与前人计算结果和实验测量结果一致性较好.对Fe15+离子的最外价电子,相对论效应对其光电离过程产生主要影响,而轨道弛豫效应则可忽略不计;对中性Na原子则情况完全不同:轨道弛豫效应的影响非常显著,但其光电离截面对相对论效应仅有非常微弱的依赖.     

100～5 000 eV下电子被等电子(Z=10)分子CH4、H2O、HF及NH3散射的总截面计算

利用可加性规则,使用Roothaan-Hartree-Fock波函数,在100～5 000 eV下首次采用由束缚原子概念修正过的复光学势,对电子被等电子(Z=10)分子CH4、H2O、HF和NH3散射的总截面进行了计算.束缚原子不同于自由原子之处,是束缚原子考虑了在不同分子中电子云的不同重叠,将计算结果与实验及其它计算结果进行了比较.结果表明,利用被束缚原子概念修正过的复光学势及可加性规则进行计算,其结果的精度要比利用未被束缚原子概念修正过的复光学势及可加性规则进行计算得到的结果好.     

Measurement of the absolute cross section for the elementary process of atomic field bremsstrahlung

Coincidence measurements of the absolute cross section for the production of bremsstrahlung by electrons in the field of gold atoms are reported. The incident electron energyT ₀ was 300 keV. Measurements were made for four different combinations of electron scattering angle and photon emission angle over a wide range of the relative photon energyk/T ₀ up tok/T ₀=0.83. The measured cross sections are compared with results of Bethe-Heitler and Elwert-Haug calculations     

Inelastic electron scattering from a Coulomb potential in a laser field

We present a theoretical study of inelastic electron scattering from a fixed Coulomb potential in the presence of a laser field, based on analytic expressions for the two-photon continuum-continuum transition matrix element. We present here the particular case of incident and scattered light polarizations orthogonal to each other and to the incident electron momentum. Results are given for the cross sections corresponding to the detection of electrons and polarized photons in coincidence, and for the detection of polarized photons only.     

Proton-nucleus elastic scattering at 1 GeV in the glauber model

Differential elastic cross sections and polarizations are calculated in a multiple-scattering formalism for proton-nucleus scattering at 1 GeV incident energy. The calculations include Coulomb and spin effects. Corrections to the Glauber model are studied. It is shown that for momentum transfer up to 2.0–2.5 fm^?1 the reaction mechanism can be taken with confidence. Consequently, fits to the experimental data over this limited range in q can be considered to extract nuclear structure information. In the present case, use has been made of nuclear densities arising from self-consistent calculations. The calculations are compared with experimental data.     

Zur Spinpolarisation langsamer Elektronen nach der Streuung an Molekülen

Cross sections and spin polarization of low-energy electrons scattered by I₂ and C₂H₅I molecules were measured in the energy range from 200 to 600 eV and angular range from 30 to 150°. At the same time, several authors made calculations of cross sections and polarizations based on the following assumptions: The molecule consists of free atoms which are independent of each other (the influence of binding is negligible) and scattering of an electron does not occur more than once within the molecule. The agreement between theory and experiment in a wide angular range justifies these assumptions for the present problems. Polarization values lower than the theoretical ones were measured only at scattering angles where the theory predicts very narrow and high values of the spin polarization. Qualitative arguments show that intramolecular scattering very likely is responsible for the deviations found between theoretical and experimental polarization peaks. By means of the polarization of the scattered intensity one can easily decide how much of the scattered intensity comes from one part of the molecule and how much comes from the other part.     

解相对论Dirac方程计算低能电子弹性散射截面的分波法

本文给出一个基于解相对论Dirac方程计算低能电子弹性散射截面的方法,比较Thomas-Fermi-Dirac(TFD)势及Hartree-Fock(HF)势对散射截面计算的影响,计算了C、Al、Cu、Ag、Au等多种元素在0.01~10keV能量范围的弹性散射截面,比较分析Mott模型、Pendry模型以及屏蔽的Rutherford截面之间的差异。     

General solution of the Dirac equation for quasi-two-dimensional electrons

The general solution of the Dirac equation for quasi-two-dimensional electrons confined in an asymmetric quantum well, is found. The energy spectrum of such a system is exactly calculated using special unitary operator and is shown to depend on the electron spin polarization. This solution contains free parameters, whose variation continuously transforms one known particular solution into another. As an example, two different cases are considered in detail: electron in a deep and in a strongly asymmetric shallow quantum well. The effective mass renormalized by relativistic corrections and Bychkov–Rashba coefficients are analytically obtained for both cases. It is demonstrated that the general solution transforms to the particular solutions, found previously (Eremko et al., 2015) with the use of spin invariants. The general solution allows to establish conditions at which a specific (accompanied or non-accompanied by Rashba splitting) spin state can be realized. These results can prompt the ways to control the spin degree of freedom via the synthesis of spintronic heterostructures with the required properties.