四种材料超晶格的价带自旋劈裂的研究

自从Esaki和Tau[1]发现量子阱和超晶格以来,人们已对由两种材料构成的量子阱及超晶格的能带结构进行了大量的研究.陈维友等人[2]已研究了三种材料构成的超晶格的能带结构.本文将利用文献[2]报道的计算方法,对由四种材料构成的超晶格价带自旋劈裂的变化规律进行研究.     

磁性硅烯超晶格中电场调制的谷极化和自旋极化

研究了基于硅烯的静电势超晶格、铁磁超晶格、反铁磁超晶格中谷极化、自旋极化以及赝自旋极化的输运性质,分析了铁磁交换场、反铁磁交换场以及化学势对输运性质的影响,讨论了电场对谷极化、自旋极化以及赝自旋极化的调控作用.结果表明:当3种超晶格的晶格数达到10以上时,在硅烯超晶格中很容易实现100%的谷极化、自旋极化和赝自旋极化,而且通过调节超晶格上的外加电场可以使极化方向发生翻转,从而在硅烯超晶格中实现外电场对谷自由度、自旋自由度以及赝自旋自由度的操控.     

光场辐照下稀磁半导体/半导体超晶格中自旋电子输运特性研究

基于单电子有效质量近似理论和传递矩阵方法,理论研究了稀磁半导体/半导体超晶格结构中电子的自旋极化输运特性.主要讨论了光场和磁场联合调制对自旋极化输运的影响,以及不同自旋电子在该超晶格结构中的隧穿时间.理论和数值计算结果表明,由于导带电子与掺杂Mn离子之间的sp-d电子相互作用引起巨塞曼劈裂,因此在磁场调制下,不同自旋电子在该结构中感受到的势函数不同而呈现出自旋过滤效应,不同自旋电子的共振透射能带的位置和宽度可以通过磁场进行调制.同时在该结构中考虑光场时,自旋依赖的透射谱会因为吸收和发射光子而呈现出对光场的强度和频率响应;最后,通过不同自旋电子的高斯波包在该结构中随时间的演化给出了不同自旋电子的隧穿时间.本文研究结果对研究和设计基于稀磁半导体/半导体超晶格结构的高速量子器件具有一定的指导意义.     

二维复式晶格磁振子晶体的带隙结构

提出了一种复式晶格磁振子晶体的模型,该模型由两种铁磁材料散射体周期排列在另一种铁磁材料基底中构成.应用超原胞的思想拓展了平面波展开法,用于数值计算研究自旋波在复式晶格磁振子晶体中的本征性质本文数值计算了由两种大小不同的铁(Fe)-铁(Fe)圆柱体交替正方排列在氧化铕(EuO)基底材料中构成的二维复式晶格磁振子晶体的带结构,研究了带隙宽度随体积填充率的变化行为,并与同一铁(Fe)圆柱正方排列在氧化铕(EuO)基底材料中构成的简单晶格磁振子晶体的带隙结构随体积填充率的变化行为进行了比较.结果表明,利用复式晶格可以优化或调节自旋波带隙的宽度和频率位置.     

超晶格结构中共振劈裂的普遍性

用传输矩阵方法研究了半导体超晶格和磁垒超晶格结构中共振劈裂效应,揭示了电子隧穿两类不同超晶格结构时共振劈裂的普遍性.其劈裂的共同特征不仅取决于超晶格的构型,而且与构筑单元的几何参数有关.在磁垒超晶格结构中,劈裂的特征还与垂直于隧穿方向的动量分量有关. 关键词：     

ZnSe—ZnTe应变层超晶格的光吸收研究

在室温下测量了Znse-ZnTe应变层超晶格的光吸收谱,观测到对应于第一轻重空穴跃迁的吸收台阶.根据测量所得的超晶格带隙确定了ZnSe-ZnTe的价带不连续为1.10eV.     

并五苯分子电荷注入导致自旋极化的密度泛函理论研究

用密度泛函理论研究了不带自旋的空穴注入并五苯后体系的自旋相关特性. 电荷注入后并五苯分子中存在自发自旋极化行为. 当注入电荷量达一定程度,分子磁矩随注入电荷量的增加呈线性增长,最大磁矩可达1 μB. 注入电荷和并五苯分子的相互作用导致分子体系结构发生变化,同时电荷密度分布及自旋密度分布也发生了变化. 注入电荷先填充自旋劈裂的碳原子p_z轨道.     

1 eV吸收带边GaInAs/GaNAs超晶格太阳能电池的阱层设计

使用In, N分离的GaInAs/GaNAs超晶格作为有源区是实现高质量1eV带隙 GaInNAs基太阳能电池的重要方案之一. 为在实验上生长出高质量相应吸收带边的超晶格结构, 本文采用计算超晶格电子态常用的Kronig-Penney模型比较了不同阱层材料选择下, 吸收带边为1 eV的GaInAs/GaNAs超晶格相关参数的对应关系以及超晶格应变状态. 结果表明: GaNAs与GaInAs作为超晶格阱层材料在实现1 eV的吸收带边时具有不同的考虑和要求; 在固定1 eV的吸收带边时, GaNAs材料作为阱层可获得较好的超晶格应变补偿, 将有利于生长高质量且充分吸收的太阳能电池有源区. 关键词： GaInAs/GaNAs超晶格 Kronig-Penney模型 太阳能电池     

半导体超晶格系统中的磁电调控电子自旋输运研究

通过采用转移矩阵方法求解自旋电子隧穿过程,理论研究了半导体超晶格系统中电子自旋输运的磁电调控行为.结果表明：仅对超晶格系统施以磁调制,隧穿系数将出现自旋分裂,随磁场增强,电导自旋极化率变大且展宽于费米能区;若选取不变磁场情况,同时施以间隔周期电场调制,超晶格的电子极化率将有更为显著地提高.进一步发现,随电场强度的改变,电子自旋输运行为显然存在两个明显不同区域,下自旋电子将在不同调制区域表现为不同的变化趋势.然而,若对周期磁超晶格施加间隔两周期的电调制,自旋电导输运的临界行为消失,电导极化率在高能区的共振峰 关键词： 半导体超晶格 自旋输运 磁电调控     

介子超精细质量劈裂的统一描述

利用能量依赖的夸克-反夸克间自旋-自旋作用势建立了介子超精细质量劈裂公式.数据分析表明该公式能统一描述基态和激发态、同位旋为零及非零介子的超精细质量劈裂.     

Electronic structures of the zinc-blende GaN/Ga1−xAlxN compressively strained superlattices and quantum wells

The electronic structures of the zinc-blende GaN/Ga_0.85Al_0.15N compressively strained superlattices and quantum wells are investigated using a 6×6 Hamiltonian model (including the heavy hole, light hole and spin-orbit splitting band). The energy bands, wavefunctions and optical transition matrix elements are calculated. It is found that the light hole couples with the spin-orbit splitting state even at thek=0 point, resulting in the hybrid states. The heavy hole remains a pure heavy hole state atk=0. The optical transitions from the hybrid valence states to the conduction states are determined by the transitions of the light hole and spin-orbit splitting states to the conduction states. The transitions from the heavy hole, light hole and spin-orbit splitting states to the conduction states obey the selection rule Δn=0. The band structures obtained in this work will be valuable in designing GaN/GaAlN based optoelectronic devices.     

Multiplet structure of P-excitons in CuBr due to valence band degeneracy

The two-photon absorption spectrum of CuBr shows a fourfold energy splitting of the 2P- and 3P-excitons of the Z_1,2 series. The splitting results from d-like contributions to the kinetic energy of the hole (Γ_δ) which lead to a coupling between angular momentum and hole spin. The energy splitting allows to determine the spherical and cubic parameters μ and δ of the reduced exciton mass. The results are compared with corresponding values of an existing band structure calculation.     

Zeeman splitting in ballistic hole quantum wires

We have studied the Zeeman splitting in ballistic hole quantum wires formed in a (311)A quantum well by surface gate confinement. Transport measurements clearly show lifting of the spin degeneracy and crossings of the subbands when an in-plane magnetic field B is applied parallel to the wire. When B is oriented perpendicular to the wire, no spin splitting is discernible up to B = 8.8 T. The observed large Zeeman splitting anisotropy in our hole quantum wires demonstrates the importance of quantum confinement for spin splitting in nanostructures with strong spin-orbit coupling.     

Orbital magnetization in semiconductors

This paper theoretically investigates the orbital magnetization of electron-doped (n-type) semiconductor heterostructures and of hole-doped (p-type) bulk semiconductors, which are respectively described by a two-dimensional electron/hole Hamiltonian with both the included Rashba spin--orbit coupling and Zeeman splitting terms. It is the Zeeman splitting, rather than the Rashba spin--orbit coupling, that destroys the time-reversal symmetry of the semiconductor systems and results in nontrivial orbital magnetization. The results show that the magnitude of the orbital magnetization per hole and the Hall conductance in the p-type bulk semiconductors are about 10^-2--10^-1 effective Bohr magneton and 10^-1--1 e²/h, respectively. However, the orbital magnetization per electron and the Hall conductance in the n-type semiconductor heterostructures are too small to be easily observed in experiment.     

Cyclotron resonance in the InAs/GaSb heterostructure in an inclined magnetic field

The mechanism of cyclotron resonance line splitting in the InAs/GaSb heterostructure in an inclined magnetic field has been studied experimentally and theoretically. It is shown that the admixing of electron and hole states leads to anticrossing of the Landau levels and, hence, to splitting of the cyclotron resonance line. In the case of an inclined magnetic field, the splitting is not observed, which is explained by the suppression of the admixing of electron and hole states due to the occurrence of an additional barrier for electrons and holes given a longitudinal magnetic field component.     

Observation of the Kondo effect in a spin-3/2 hole quantum dot

We report the observation of Kondo physics in a spin-3/2 hole quantum dot. The dot is formed close to pinch-off in a hole quantum wire defined in an undoped AlGaAs/GaAs heterostructure. We clearly observe two distinctive hallmarks of quantum dot Kondo physics. First, the Zeeman spin splitting of the zero-bias peak in the differential conductance is independent of the gate voltage. Second, this splitting is twice as large as the splitting for the lowest one-dimensional subband. We show that the Zeeman splitting of the zero-bias peak is highly anisotropic and attribute this to the strong spin-orbit interaction for holes in GaAs.     

Enhanced coupling of plasmons in hole arrays with periodic dielectric antennas

We compare the angle-dependent transmission spectra of a metal hole array with dielectric pillars in each hole with that of a conventional metal hole array. The pillars enhance the optical transmission as well as the interaction between surface plasmon modes. This results in an observed splitting Delta omega/omega as large as 6%, at normal incidence, for the modes on the pillar side of the array.     

Theoretical models for the interpretation of E.S.C.A. spectra

Three features of E.S.C.A. spectra are discussed: the chemical shift, multiplet splitting, and satellite bands. In the chemical shift effect a perturbation theory treatment shows that the electronic relaxation energy in the hole state of the molecules can be attributed to a flow of electrons on to the ionized atom. Thus the relative abilities of surrounding atoms to “feed” electrons to the ionized atom determines the relative importance of the relaxation energy contribution to the chemical shift. This explains why neutral atom charges don't always determine the direction of the chemical shift. In multiplet splitting the same perturbation treatment shows that the sign and magnitude of the relaxation energy contribution to the multiplet splitting is determined by the direction and magnitude of flow of majority electron spin density in going to the relaxed hole state. Unrestricted Hartree-Fock calculations on the series MF ₂, with M first row transition metals, are compared with E.S.C.A. experiments on the corresponding octahedral complexes to show that complex ion formation has only a very small effect on core level multiplet splitting. Relaxed hole state calculations on a series of first row atom (C,N,O,F) containing radicals leads to the conclusion that in these cases correlation energy effects are larger for the high spin multiplets than for the low spin multiplets. The assignments of satellite structure in transition metal complexes is reviewed and multiconfiguration self-consistent field results are presented and discussed for the satellite structure     

Light transmission through metal films perforated with arrays of asymmetric cross-shaped hole

The transmission characteristics of metallic film perforated with an array of asymmetric cross-shaped hole are studied by using the three-dimensional finite difference time-domain method. We find that the wavelengths and intensities of transmission peaks depend strongly on the asymmetric parameters of the cross-shaped hole. The transmission peaks in the structure of asymmetric cross-shaped hole array originate from the splitting of the transmission peak in the corresponding one of symmetric cross-shaped hole array. Moreover, it is also found that the transmission spectra can be adjusted by changing other geometrical parameters of asymmetric cross-shaped hole due to the their effect on the distribution of the oscillating charges on metal surfaces.     

用于ICF光路调整的分光照明元件设计

在惯性约束核聚变激光驱动装置中,光路庞大复杂且元器件众多,为保证激光系统正常运行需对光路进行精密调节。特别是装置中的多个4F系统,需调整激光光路使其聚焦后对准焦平面滤波小孔中心,以保证激光顺利通过并实现低通滤波作用。目前实际工程中采用凹透镜背光照明的方法判断光束是否准确过孔,但该方法步骤繁琐且调整精度较低,给实际光路调整带来了极大的不便。本文基于全息原理,提出了一种简单高效的4F系统光路调整方法,通过一特殊设计的分光照明衍射光学元件,可一步实现激光聚焦过孔的判断与调整,可有效解决现有4F系统光路调整的困难。