BOUND POLARONS IN ASYMMETRIC QUANTUM WELLS IN AN ELECTRIC FIELD

We have proposed the Hamiltonian of a polaron bound to a donor impurity in semiconductor quantum wells (QWs) in the presence of an electric field. The couplings of an electron with the confined bulk like longitudinal optical (L₀) phonons, halfspace L₀ phonons and interface phonons are considered. In particular, the interaction of the impurity with the various phonon modes is also included. We have calculated the ionization energy of a bound polaron in Al_xl Ga_1-xl As/GaAs/Al_xr Ga_1-xr As asymmetric and symmetric QWs. Results are obtained as a function of the barrier height (or equivalently of Al concentration x),the well width, the electric field intensities and the position of impurity in the QWs. Our numerical calculations show clearly that the interaction between the impurity and the phonon field plays an important role in screening the Coulomb interaction. It is shown that for at hin well (＜12nm), the cumulative effects of the electronphonon coupling and the impurityphonon coupling can contribute appreciably to the donor ionization energy and polarizability.     

介电受限对量子点中受限激子的影响

在有效质量近似下,采用有限深势阱模型研究了强受限制范围内,介电受限对球形,立方形半 量子点中受限激子的影响,结果表明在考虑表面极化效应以后,量子点的形状对受限激子的影响是不可忽略的。     

极性晶体内表面电子的量子像势及其极化子的有效势

本文从与真空接触的存在二支声子的半无限极性晶体表面附近极化子的哈密顿算符入手，应用二支模型理论，分别对GaAs和ZnO两种材料计算了内表面电子的量子像势及其极化子的有效势。计算结果表明：当Z很小时，经典像势和半经典有效势分别与量子像势和量子有效势相差较大；当Z很大时，经典像势和半经典有效势分别是量子像势和量子有效势的一个很好的近似。     

量子力学中的二维散射问题

研究了量子力学中的二维散射问题，讨论了分波法和Ｂｏｍ近似法，并计算了一些实例。     

QUANTUM DIFFUSION IN TWO-DIMENSIONAL OCTAGONAL QUASICRYSTALS

We have studied the quantum diffusion in an octagonal quasiperiodic tiling. Paticular attention is paid to the analysis of long-time behavior of the autocorrelation function C(t) and the relationship between diffusion and fractal dimensions of energy spectrum. For the pure hopping model, numerical calculations show that C(t)～t^-1 , which corresponds to the case of periodic systems. For the combined model, in which the contribution of site potentials is considered, C(t)～t^-δ with 0＜δ≤1. The scaling factor δ is related to Hamiltonian parameters and the type of site where electron is initially located. Moreover, we find a crossover from δ=1 to 0＜δ＜1 with increasing site potentials.     

AN EFFECTIVE TWO-LEVEL CHANNEL FOR AN IMPURITY IN A SUPERLATTICE

The eigenstates and eigenspectrum of a charged particle in a one-dimensional semiconductor superlattice with an impurity under the action of a dc electric field are investigated employing the single-band tight-binding model. We find that the system undergoes a series of avoided crossings, at which resonant oscillations between the impurity and its nearest neighbour occur if appropriate conditions are met, suggesting an effective two-level approximation. This phenomenon shows that introducing an impurity in a perfect lattice provides a promising structure for the observation of terahertz radiation.     

超导量子比特中的量子跳跃方法

量子力学自建立以来很长一段时间被当作是描述系综运动的理论.但是上世纪80年代对冈禁离子和原子的研究观测到了量子跳跃现象,迫使人们发展了一些能够用于单量子系统的方法,其中之一就是量子跳跃方法.本文总结了我们近来把量子跳跃方法应用到以约瑟夫森隧道结为基础的超导量子比特的工作.我们不但实验观测到宏观量子系统中的量子跳跃,还可以利用量子跳跃现象来研究固体中普遍存在的两能级系统及其引起的超导量子比特中的退相干.     

ELECTRON-INTERFACE PHONON SCATTERING IN ASYMMETRIC SEMICONDUCTOR QUANTUM WELL STRUCTURES

Electron-interface phonon scattering rates in asymmetric single quantum well and step quantum well structures are calculated by means of the interaction Fr?hlich-like Hamiltonian between an electron and interface optical phonons in a four-layer heterostructure given re-cently. The intrasubband and intersubband electron scattering rates are given as functions of quantum well width, step width and step height. We have found that the electron scattering depends strongly on the potential parameters and the usual selection rules for these tran-sitions are broken down in asymmetric heterostructures; the interface LO modes are more important than the interface TO modes for the electron-interface phonons scattering in het-erostructures; the intrasubband scattering rates are insensitive functions of step width and step height, and the intersubband scattering rates are complicated functions of step height and step width in step quantum wells. Moreover, we have also observed that the scattering rates for intrasubband and intersubband transitions have no obvious changes in the case that the first or second subband energy level crosses the step height in a step quantum well.     

VARIATIONAL CALCULATION ON GROUND-STATE ENERGY OF BOUND POLARONS IN PARABOLIC QUANTUM WIRES

Within the framework of Feynman path-integral variational theory, we calculate the ground-state energy of a polaron in parabolic quantum wires in the presence of a Coulomb potential. It is shown that the polaronic correction to the ground-state energy is more sensitive to the electron－phonon coupling constant than the Coulomb binding parameter, and it increases monotonically with decreasing effective wire radius. Moreover, compared to the results obtained by Feynman Haken variational path-integral theory, we obtain better results within the Feynman path-integral variational approach (FV approach). Applying our calculation to several polar semiconductor quantum wires, we find that the polaronic correction can be considerably large.     

AN IMPROVED EFFECTIVE POTENTIAL APPROACH TO DYNAMICAL SYMMETRY BREAKING

We have developed, in this paper, a method for evaluating effective potential for local composite fields based on loop expansion by first renormalizing the generating functional of connected Green's functions and then making the Leqendre transformation. A consistency condition reflecting the fact that no condensate effect occurs at tree level is proposed, which plays an important role in this method. The method is illustrated through the Gross-Neveu model. This method can be applied to a wider class of models than can the auxiliary field method.     

量子点中双极化子束缚能的研究

本文采用费曼路积分对量子点中大极化子的基态能进行了变分计算,得出了适用于较大范围的电声耦合区间和量子点限制势强度的双极化子束缚能。进一步通过数值计算以及理论分析研究了双极化子束缚能（BE）、介电常数比（η）、电声耦合常数（α）以及量子点限定势（Ω）这些物理量之间的关系。并得出结论：随限定势强度的增加,束缚能、临界电声耦合常数并不呈单一增大或减小,存在一个关键的限定势,当限定势到达该值时,最有利于双极化子的形成。     

AN APPROACH TO RAYLEIGH MODEL OF EFFECTIVE CONDUCTIVITY TENSOR OF COMPOSITE

Using a new approach to Rayleigh model of composite, we obtain the complete solutions for many systems of orthorhombic., The evaluation of the effective conductivity tensor of the composite with anisotropic,structure,is also discussed in detail for the first time.     

PROPERTIES OF PROPAGATION OF GUIDED ELECTRON WAVES IN COUPLED ASYMMETRIC QUANTUM WELLS

In this article we investigate the properties of the propagation of guided electron waves in the coupled asymmetric quantum wells. By decomposing the eigenfunctions of electron in the coupled double quantum wells in terms of the basis eigenfunctions of the individual wells, the expression of the mode amplitude func-tions for various bare states in wells has been given. By setting up appropriate boundary conditions one can simulate different injecting manners of electron into the system and study how the electron waves trans-fer among various states. The major electron wave transfer happens between the matching bare states in wells. The particular pattern of the transfer depends on the injecting manner and the energy of the inci-dent electron. We also show the influence of the presence of the multimodes on the variatinn of the mode amplitude functions. It leads to producing some oscillations imposed on the original sinusoidal-like func-tions and causing incomplete transfer between a pair of states in channels due to the beating frequency effect or the interference among various modes.     

量子化学中有限元法的并行计算

在有限元方法的框架下,将量子化学中的基组展开方法和普通有限元方法结合起来,提出了一个新方案。在曙光1000并行机上,采用新方案,计算了Li₂、LiH、BH分子的基态总能量。新方案在相同计算量下,可获得比普通有限元方法高得多的精度。     

量子阱非对称法布里-珀罗腔调制器电折变模式蓝移

对于从实验中观察到的GaAs/GaAlAs多量子讲非对称法布里一哨罗腔调制器中电致折射率变化引起的模式蓝移现象,从理论上予以讨论.利用等效光程方法分析了电致折射引起的模式的移动特性,实验和理论符合较好.     

EXCITON ENERGY OF THE InAs/GaAs SELF-ASSEMBLED QUANTUM DOT IN A SEMICONDUCTOR MICROCAVITY

We report on the theoretical study of the interaction of the quantum dot (QD) exciton with the photon waveguide models in a semiconductor microcavity. The InAs/GaAs self-assembled QD exciton energies are calculated in a microcavity. The calculated results reveal that the electromagnetic field reduces the exciton energies in a semiconductor microcavity. The effect of the electromagnetic field decreases as the radius of the QD increases. Our calculated results are useful for designing and fabricating photoelectron devices.     

极性晶体外表面电子的量子像势及其极化子的基态能量

本从与真空接触的存在二支声子的半无限极性晶体表面附近极化子的哈密顿算符入手，应用二支模型理论，分别对GaAs和ZnO两种材料计算了外表面电子的量子像势及其极化子的基态能量，计算结果表明，利用二支模型理论求出的外表面极化子的基态能量与利用一支模型理论求出的外表在面极化子的基态能量相差较大，对GaAs，误差约为31.1%, 对ZnO，误差约为14.8%。     

分光计实验中望远镜的快速调节方法——台先镜后法

在分光计实验中,调整望远镜光轴与分光计主轴大致垂直是最关键、最难调的一步．实验中容易观察到平面镜一个面反射回的“十”字像,却较难调出两个面反射回的“十”字像．本文利用光路图进行了分析,提出了一个快速、有效的调整方法——台先镜后法．     

由扁平超导体表面磁场反演二维体电流密度分布的一种有效方案

本文介绍一种由扁平超导样品表面垂直磁场分布反演体电流密度分布的有效方案。依据二维情形超导样品表面的磁光测量获得的局域垂直场分布,借助于磁偶极矩与磁偶极矩激发磁场的关系,利用物理问题的对称性,由求解线性方程组的共轭梯度数学方法,反演二维情形下的电流密度分布。     

提高QUAT序列累加效率的一个有效方法

本文介绍一种产生不连质子的¹³C核NMR谱的脉冲序列,并对该序列提出了改进意见。在FX-90Q型NMR谱仪上证实了这种改进对提高累加效率和减小谱线的强度失真具有明显效果。