Energy Spectrum of a Positronium Negative Ion in a Parabolic Quantum Well

The method of few-body physics is applied to calculating the energy levels of low-lying states ofa positro-nium negative ion in a parabolic quantum well. The results show that the energy levels of a positronium negativeion intwo-dimensional case are lower than those in three-dimensional case.     

量子阱中二维电子气的性质

利用提出的三维不对称方势阱模型，对半导体量子阱中二维电子气的性质进行了研究，确定其量子能级和费米能量，并对有关结果进行了讨论。     

抛物阱中极化子效应对D-心的影响

采用改进的LLP方法在考虑体声子影响的情况下研究了抛物量子阱中电子-LO声子相互作用对D^-心能量的影响.研究结果表明,阱宽较小时,D^-心的基态能量和结合能随着阱宽L的增大而急剧减小;阱宽较大时,能量的减小比较缓慢,最后接近体材料中的三维值.并且得出了电子-LO声子相互作用可使D^-心的结合能有显著的提高.     

Fractional-dimensional approach for biexcitons in GaAs/AlxGa1−xAs quantum wells

The energy of a biexciton in a GaAs/Al_xGa_1?xAs quantum well structure with finite barriers is investigated by using the geometrical model of two-dimensional biexcitons proposed by Singh et al. [J. Singh, D. Birkedal, V.G. Layssenko, J.M. Hvam, Phys. Rev. B 53 (1996) 15909; I.-K. Oh, J. Singh, Phys. Rev. B 60 (1999) 2528]. A fractional-dimensional approach is used to obtain the binding energy of the biexciton in both square quantum wells and parabolic quantum wells. Theoretical results show that the binding energy of a biexciton in a finite quantum well exhibits a maximum with increasing well width. The ratio of the binding energy of a biexciton to that of an exciton in a quantum well structure is found to be sensitive to the electron-to-hole mass ratio and larger than that in the three-dimensional system. The results agree fairly well with previous experimental results. The results of our approach are also compared with those of earlier theories.     

Finite element distributions in statistical theory of energy levels in quantum systems

The probability density functions of the three-point finite elements of the three adjacent energy levels for the three-level quantum system are introduced as a supplementary characteristics of quantum chaos. The three-level quantum system is studied. The probability density functions of the second difference and asymmetrical three-point first finite element are computed for the three-dimensional Gaussian orthogonal ensemble GOE(3), the three-dimensional Gaussian unitary ensemble GUE(3), the three-dimensional Gaussian symplectic ensemble GSE(3), as well as for the Poisson ensemble PE.     

Energy Spectra of Excitons Bound to a Neutral Acceptor in Quantum Dots

The energy spectra of the ground state for an exciton (X) trapped by a neutral acceptor (A⁰) in a quantum dot with a parabolic confinement have been calculated as a function of the electron-to-hole mass ratio σ by using the hyperspherical coordinates. We find that the (A⁰,X) complex confined in a quantum dot has in general a larger binding energy than those in a two-dimensional quantum well and a three-dimensional bulk semiconductor, and the binding energy decreases with the increase of the electron-to-hole mass ratio.     

Study of the electric capacitance spectra on symmetric quantum-dot pattern

We have calculated the ground-state energy of the symmetric quantum-dot pattern by the ab initio calculation method, i.e. unrestricted Hartree-Fock-Roothaan (UHFR) method based on the Gaussian basis, and studied their electric capacitance spectra, assuming each quantum dot of quantum-dot pattern to be confined in a three-dimensional spherical potential well of finite depth. For the systems in question, our results show that our method and theoretical model not only give the electric capacitance peaks similar to s-shell and p-shell atom-like quantum dot, but also show some new fine-structure of electric capacitance in the symmetric quantum-dot pattern system. This method might be a feasible tool to study few-electron problems on the symmetric quantum-dot pattern system.     

声子之间相互作用对量子点中极化子性质的影响

研究了抛物量子点中弱耦合极化子的性质。采用线性组合算符和微扰法,导出了抛物量子点中极化子的基态能量。当计及电子在反冲效应中发射和吸收不同波矢的声子之间的相互作用时,讨论了对量子点中极化子的基态能量的影响。通过数值计算,结果表明,量子点中极化子基态能量随量子点的有效受限长度的减小而迅速增大,随电子-LO声子的耦合强度的增加而减少。当l₀>1.4时,声子之间的相互作用不能忽略。     

Features of underwater echo extraction based on signal sparse decomposition

In order to better realize sound echo recognition of underwater materials with heavily uneven surface,a features ion method based on the theory of signal sparse decomposition has been proposed.Instead of the common time frequency dictionary,sets of training echo samples are used directly as dictionary to realize echo sparse decomposition under L₁ optimization and a kind of energy features of the echo.Experiments on three kinds of bottom materials including the Cobalt Crust show that the Fisher distribution with this method is superior to that of edge features and of Singular Value Decomposition （SVD） features in wavelet domain.It means no doubt that much better classification result of underwater bottom materials can be obtained with the proposed energy features than the other two.It is concluded that echo samples used as a dictionary is feasible and the class information of echo introduced by this dictionary can help to obtain better echo features.     

Exchange and spin states in quantum dots under strong spatial correlations. Computer simulation by the Feynman path integral method

The fundamental laws in the behavior of electrons in model quantum dots that are caused by exchange and strong Coulomb correlations are studied. The ab initio path integral method is used to numerically simulate systems of two, three, four, and six interacting identical electrons confined in a three-dimensional spherical potential well with a parabolic confining potential against the background of thermal fluctuations. The temperature dependences of spin and collective spin magnetic susceptibility are calculated for model quantum dots of various spatial sizes. A basically exact procedure is proposed for taking into account the permutation symmetry and the spin state of electrons, which makes it possible to perform numerical calculations using modern computer facilities. The conditions of applicability of a virial energy estimator and its optimum form in exchange systems are determined. A correlation estimator of kinetic energy, which is an alternative to a basic estimator, is suggested. A fundamental relation between the kinetic energy of a quantum particle and the character of its virtual diffusion in imaginary time is demonstrated. The process of natural “pairing” of electron spins during the compression of a quantum dot and cooling of a system is numerically reproduced in terms of path integrals. The temperature dependences of the spin magnetic susceptibility of electron pairs with a characteristic maximum caused by spin pairing are obtained.     

The Spectra of Low-Lying States of Three-Dimensional Quantum Dots in a Magnetic Field

We have studied three-electron systems in three-dimensional anisotropic parabolic quantum dots with the cylindrical symmetry in magnetic fields by means of the method of few-body physics. The results show that the energy levels of a number of states are the lowest, as the magic angular momentum states of two-dimensional quantum dots.     

Symmetry adapted harmonic oscillator functions

Quantum mechanical excited energy states of two- or three-dimensional harmonic oscillators are highly degenerate. A general method is presented to calculate the symmetry adapted quantum mechanical oscillator functions with respect to the symmetry group of the oscillator. In the special case of the tetrahedral symmetry group the method is demonstrated by detailed formulas for the two- and three-dimensional case. A computer program is also available. The method can easily be modified for other symmetry groups.     

氮化物抛物量子阱中类氢杂质态能量

采用变分方法研究氮化物抛物量子阱(GaN/Al_xGa_1-xN)材料中类氢杂质态的能级,给出基态能量、第一激发态能量、结合能和跃迁能量等物理量随抛物量子阱宽度变化的函数关系.研究结果表明,基态能量、第一激发态能量、基态结合能和1s→2p±跃迁能量随着阱宽L的增大而减小,最后接近于GaN中3D值.GaN/Al_0.3Ga_0.7N抛物量子阱对杂质态的束缚程度比GaAs/Al_0.3Ga_0.7As抛物量子阱强,因此,在GaN/Al_0.3-Ga_0.7N抛物量子阱中束缚于杂质中心处的电子比在GaAs/Al_0.3Ga_0.7As抛物量子阱中束缚于杂质中心处的电子稳定.     

量子阱数量变化对双波长LED作用的研究

采用软件理论分析的方法分析了InGaN/GaN量子阱数量变化对双波长发光二极管发光光谱、内量子效率、电子空穴浓度分布、溢出电流等产生的影响.分析结果表明,量子阱数量的增加会引起载流子分配不均的现象,所以量子阱数量的增加并不能有效地提升载流子复合率、内量子效率和发光强度,还会引起开启电压升高的现象,影响能量转化效率.此外,不同发光波长的量子阱数量的增加会引起发光光谱强度的变化. 关键词： 量子阱 数量 数值模拟 双波长发光二极管     

Two Interacting Electrons in a Spherical Gaussian Confining Potential Quantum Well

Two-electron states of a three-dimensional spherical GaAs quantum dot (QD) with a Gaussian confining potential confinement are studied. Calculations are made by using the method of few-body physics within the effectivemass approximation. We have calculated the energy levels of single and triplet states as functions of the range and depth of the confining potential well in the spherical QDs. The same calculations performed with the parabolic approximation of the Gaussian potential lead to the results, which are qualitatively and quantitatively different.     

无限深量子阱中强耦合极化子的基态结合能

研究了无限深量子阱中极化子的基态性质,采用线性组合算符和变分相结合的方法导出了强耦合极化子的振动频率λ、基态能量E₀和基态结合能E_b,讨论了阱宽L和电子-LO声子耦合强度α对强耦合极化子的振动频率λ、基态能量E₀和基态结合能E_b的影响。通过数值计算,结果表明:强耦合极化子的振动频率和基态结合能随阱宽L的增大而减小,随电子-LO声子耦合强度α的增强而增大;基态能量随阱宽L的增大而减小,其绝对值随电子-LO声子耦合强度α的增强而增大;当量子阱阱宽L趋近于无限大和无限小两种极限情况下,分别与三维和二维极化子的结果相一致。     

无限深势阱问题的可视化研究

基于计算软件对一些常见的无限深势阱进行了可视化研究,并设计了GUI界面实现对势阱的选择.在选定势阱后,设置好相应的势阱参数和量子数,便可依次绘制出低维势阱的波函数、概率密度函数和三维势阱中的电子云图像.文中分析了二维和三维势阱中能级的简并度问题,并重点讨论了不同势阱波函数和概率密度函数随量子数的变化规律.将势阱问题可视化可以方便分析不同条件下波函数的物理图像,有助于量子力学课程中的教师教学与学生学习.     

Estimating ground-state properties of quantum dot arrays using a local Thomas-Fermi-Dirac approximation

An exactly solvable local Thomas-Fermi-Dirac approximation is applied to the calculation of the ground-state density of three-dimensional quantum dot arrays, where we give estimates to properties like total energy, chemical potential, and differential capacitance. Numeric examples are calculated for pairs of quantum dots using a Gaussian confining potential. The computational complexity of the present method is linear in the number of electrons and centers of the system.