Rashba自旋-轨道相互作用影响下量子盘中强耦合磁极化子性质的研究

本文基于Lee-Low-Pines幺正变换法,采用Tokuda改进的线性组合算符法研究了Rashba自旋-轨道相互作用效应下量子盘中强耦合磁极化子的性质.结果表明,磁极化子的相互作用能Eint的取值随量子盘横向受限强度ω0、外磁场的回旋频率ωc、电子-LO声子耦合强度α和量子盘厚度L的变化均与磁极化子的状态性质密切相关;磁极化子的平均声子数N随ωc,ω0和α的增加而增大,随L的增加而振荡减小;在Rashba自旋-轨道相互作用效应影响下磁极化子的有效质量将劈裂为m*+,m*-两种,它们随ωc,ω0和α的增加而增大,随L的增加而振荡减小;在研究量子盘中磁极化子问题时,电子-LO声子耦合和Rashba自旋-轨道相互作用效应的影响不可忽略,但Rashba自旋-轨道相互作用和极化子效应对磁极化子的影响只有在电子运动的速率较慢时显著.     

Study of Two-Mode Squeezed Magnetopolarons

In this paper, we conduct an investigation into two-dimensional squeezed magnetopolarons. The Hamiltonian of magnetopolarons is dealt with two-mode squeezed states transformation, which is based on the Lee-Low-Pines and Huybrechts （LLP-H） canonical transformations. This method makes it possible to take account of the linear terms, bilinear ones of phonon operators, and the correlation between two longitudinal optical （LO） phonon modes. The energies of the ground state and excited states are evaluated by variational approach, and accurate results are obtained. Furthermore, the renormalized cyclotron masses for some possible transitions are discussed in detail.     

Study of two-dimensional squeezed magnetopolarons

In this Letter, some properties of two-dimensional squeezed magnetopolarons are investigated. The Hamiltonian of magnetopolarons is dealt with by using squeezed state transformation, which is based on the Lee–Low–Pines and Huybrechts (LLP–H) canonical transformations. This method makes it possible to consider bilinear terms of the phonon operators as well as linear terms arising from the LLP–H transformations. Some exact results are obtained, such as the energies of ground and excited states for squeezed magnetopolarons and renormalized cyclotron masses for some possible transitions.     

Influence of phonon dispersion and exciton spectrum on the energy spectrum of magnetopolarons in a quantum well

An analysis is made of the influence of the spatial dispersion of LO phonons and the exciton effect on the energy spectrum of magnetopolarons in a quantum well. It is shown that in optical experiments where light is incident normally on the plane of the quantum well, a discrete spectrum of magnetopolarons is observed. Both the phonon dispersion and the Coulomb attraction of an electron and a hole may lead to a shift of the discrete magnetopolaron energy levels and additional contributions to the broadening of various levels.     

Built-in electric field effect on cyclotron mass of magnetopolarons in a wurtzite In_xGa_（1-x）N/GaN quantum well

The cyclotron mass of magnetopolarons in wurtzite In x Ga 1 x N/GaN quantum well is studied in the presence of an external magnetic field by using the Larsen perturbation method.The effects of the built-in electric field and different phonon modes including interface,confined and half-space phonon modes are considered in our calculation.The results for a zinc-blende quantum well are also given for comparison.It is found that the main contribution to the transition energy comes from half-space and interface phonon modes when the well width is very small while the confined modes play a more important role in a wider well due to the location of the electron wave function.As the well width increases,the cyclotron mass of magnetopolarons first increases to a maximum and then decreases either with or without the built-in electric field in the wurtzite structure and the built-in electric field slightly reduces the cyclotron mass.The variation of cyclotron mass in a zinc-blende structure is similar to that in a wurtzite structure.With the increase of external magnetic field,the cyclotron mass of polarons almost linearly increases.The cyclotron frequency of magnetopolarons is also discussed.     

Energy levels of impurity magnetopolarons in parabolic quantum wires

A variational perturbative method is established to calculate the energy levels of impurity magnetopolarons in parabolic quantum wires for arbitrary values of electron-phonon coupling constant α, Rydberg constant R, frequency of the parabolic potential ω and cyclotron frequency ω_c. Numerical results are derived and discussed for the energies of the ground state and the first excited state.     

Charge ordering and magnetopolarons in Na0.82CoO2

Using spectral ellipsometry, we measured the dielectric function of a Na(0.82(2))CoO2 crystal that exhibits bulk antiferromagnetism with T(N)=19.8 K. We identify two prominent transitions as a function of temperature. The first one at 280 K involves marked changes of the electronic and lattice responses that are indicative of charge ordering in the CoO2 layers. The second transition occurs around T(N)=19.8 K and reveals sizable spin-charge coupling. The data are discussed in terms of charge ordering and formation of magnetopolarons due to a charge-induced spin-state transition of adjacent Co3+ ions.     

束缚磁极化子的性质

采用线性组合算符和幺正变换方法分别导出弱、强耦合情形下束缚磁极化子的振动频率和基态能量.结果表明库仑场的存在使得磁极化子的基态能量的绝对值变小.     

弱耦合多原子半无限晶体中磁极化子的激发能量

近年来国内外对多原子极性晶体中磁极化子性质的研究十分活跃,Zorkani等采用变分法计算了束缚磁极化子的基态能量,Kandemir等采用束缚朗道态讨论了二维大磁极化子的基态和第一激发态能量,国内一些学者采用微扰法和新颖算符法讨论了多原子极性晶体中表面和体磁极化子的性质。采用线性组合算符和幺正变换,研究磁场中多原子半无限极性晶体中电子和光学声子弱耦合相互作用所产生的极化子的第一激发态能量及平均声子数。结果表明:当电子无限接近晶体表面时,磁极化子的基态能量仅为Landau能量;第一激发态能量为Landau基态能量的2倍;平均声子数等于各支与电子耦合的体光学声子数和表面光学声子数之和。而当电子处于晶体深处时,磁极化子的基态能量却为Landau基态能量与各支体光学声子以及表面光学声子分别耦合的能量之和;第一激发态能量仍为Landau基态能量的2倍;平均声子数等于各支与电子耦合的体光学声子数和与所处深度有关的各支体光学声子数之和,而与各支表面光学声子无关。     

表面磁极化子的光学声子平均数

采用Tokuda改进的线性组合算符、Lagrange乘子和变分法,讨论了强、弱耦合表面磁极化子的性质。计算了极化子的基态能量和光学声子平均数。以AgCl和ZnS晶体为例进行了数值计算。讨论了表面磁极化子振 动频率、基态能量和光学声子平均数与磁场B和拉格朗日乘子u的关系。     

表面极化子光学声子平均数的磁场和温度依赖性

采用变分法、幺正变换和拉格朗日乘子法,研究了有限温度下纯二维晶体中表面磁极化子的性质.讨论了表面光学声子平均数、磁极化子振动频率λ与磁场B、温度T及Lsgrange乘子u之间的关系.对KCl晶体进行了数值计算,结果表明:磁极化子振动频率、表面光学声子平均数均随磁场B的增强而增加,且随温度T升高而增加.当bgrange乘子u超出慢电子范围时磁极化子振动频率、表面光学声子平均数均随u增加而增大且变化越来越显著.     

Magnetopolaron states involving confined phonons in a semiconductor quantum well

Energy splitting ΔE _res in double magnetopolaron energy spectrum in rectangular quantum wells as functions of the well width d have been calculated. We have considered in the capacity of interaction leading to resonant coupling between electrons and phonons the interaction with confined phonons and (for comparison) with bulk LO phonons. We have obtained the conditions when the interaction with bulk phonons yields correct results. Calculations for AlAs/GaAs/AlAs and AlSb/InSb/AlSb structures have been performed. Alongside the parameter ΔE _res for a polaron, whose resonant magnetic field is determined by the condition Ω=ω _L1, where Ω is the cyclotron frequency and ω _L1 is the LO phonon frequency in the quantum well (A-polaron), we have calculated ΔE _res for D-(Ω=2ω _L1) and F-polarons (Ω=3ω _L1), which is a factor of $\sqrt 2 $ and $\sqrt 3 $ , respectively, smaller than ΔE _res for the A-polaron. Since the splitting ΔE _res for the A-polaron is very large (up to 0.2?ω _L1), it is more convenient to study in experiments D-and F-polarons since their resonant magnetic fields are lower. We have predicted existence of “weak” magnetopolarons, in which the splitting is proportional to a higher power of Frölich’s coupling constant α than α ^1/2.     

On the most accurate measurements of the wavelengths of X-ray spectral lines

The paper discusses the influence of statistical errors in measuring the intensity of a spectral line on the exact determination of its wavelength. Using simplifying assumptions, it is shown that the relative error in measuring the wavelengths of spectral lines of the same type, caused by the statistical character of X-ray intensity measurements and by the influence of the true width of the spectral line, is practically constant under the same conditions, i.e. it is independent of the lattice parameters of the crystals used and of the wavelength of the spectral line. It seems that the latest exact measurements of Bearden confirm this result.The greatest care should therefore be devoted to the neighbourhood of inflection points of the curve representing the spectral line profile when making exact measurements of the spectral position of the lines.The author heartily thanks Professor M. A. Blochin for valuable remarks on this work.     

耳蜗中tip-link张力与静纤毛运动动力学研究

诠释耳蜗的主动感音放大机制一直是未解的医学难题.这种机制与耳蜗中外毛细胞顶端的静纤毛运动密切相关,静纤毛运动又受到tip-link张力与淋巴液流体力的调节.因此,研究静纤毛运动过程中tip-link张力是诠释耳蜗的主动感音放大机制的重要环节.本文把静纤毛视为变形体,基于泊肃叶流动理论并结合分布参数模型,推导了静纤毛运动的解析解.研究了盖膜剪切荷载作用下静纤毛和淋巴液相互作用的动力响应以及tip-link张力的变化规律.研究发现:当静纤毛的杨氏模量减小时,在小于峰值频率的区域,tip-link张力显著增大,f₂的峰值频率减小.以往的研究将静纤毛作为刚体,势必导致低频声音信号作用减弱.当系数c=0 (无黏性阻力)时,f₂频率选择特性存在;当μ=0(无压力)时,f₂频率选择特性消失,因此淋巴液可能是通过在静纤毛间产生压强的方式来调节毛束的频率特性的.另外,盖膜剪切荷载频率越高,静纤毛轴弯曲越明显,发束内外域的压强差也越大.     

线型分子的电子能级之Λ分裂的新解释

认为电子态能级发生Λ分裂虽然是角动量引起的,但不是耦合而是运动牵连作用的结果.从这一认识出发,利用欧拉方程和拉格朗日方程分别得到了包含Λ分裂的分子转动哈密顿函数和哈密顿算符,所得结果与Van.Vleck的著名结论完全一致 关键词： Λ分裂 线型分子 欧拉方程 哈密顿算符     

Nonlinear optical response of an atom in the field of femtosecond laser pulses with near-atomic intensity

A theory of the nonresonant response of a single atom in a state with arbitrary magnitude and direction of the angular momentum of an atomic electron with respect to the polarization vector of the acting electromagnetic field has been developed. It has been shown that the atomic response current has a tensor structure and depends both on the direction of the angular momentum of the atom and on the polarization vector of the external field. The tensor character of the response is due to the effects of the anisotropy of probability density distribution of the atomic electron as compared to the case of the free atom. The selection rules for the axisymmetric problem of the atom in the field have been analyzed. The manifestation of the selection rules in the angular spectra of photoelectrons has been demonstrated. The probability of the ionization of the atom has been analyzed as a function of the amplitude and duration of the pulse. It has been shown that the width of the generation spectrum is a nonlinear function of the field strength and is saturated in the region of nearly atomic fields. Methods for controlling the parameters of the atomic response spectrum have been proposed on the basis of the use of a sequence of laser pulses with various time profiles, carrier frequencies, and polarization states. It has been shown that the generation of terahertz radiation is possible in the preionization regime, where the generation mechanism is attributed to atomic nonlinearity.     

Statistical theory of a solvated electron in an electrolyte

The behavior of a solvated electron in an electrolyte is investigated. The formalism of the theory is based on variational estimation of path integrals. It reduces the problem to the investigation of the self-consistent mean field produced by the ions and the electron. Mayer cluster expansions make it possible to take account of the short-range interactions and to find expressions for the effective potential of the electron and the electron-ion and electron-neutral atom correlation functions as a function of the macro-and microscopic parameters of electrolytes. In the limit of high ion densities the behavior of the electron is determined solely by the Coulomb interaction, which results in the formation of a polaron state. This state of the electron is virtually independent of the thermodynamic parameters of the electrolyte. In the opposite limit of low ion densities the electron forms a cavity state. The presence of ions results in additional localization of the electron and is manifested experimentally as a shift of the absorption band in the direction of high energies. The estimated shift for a hydrated electron agrees with the experimental data. Zh. éksp. Teor. Fiz. 115, 1463–1477 (April 1999)     

固体火箭发动机羽流辐射光谱测温方法研究

固体火箭发动机羽流具有高温、高速与强辐射特征,羽流温度是发动机工作状态与性能的重要表征参数。准确测量固体火箭发动机羽流温度对了解发动机内部燃烧情况以及发动机综合性能具有重要的参考价值。随着激光与光谱学的发展,激光光谱技术逐步应用于固体推进剂燃烧及发动机羽流温度测量。辐射光谱测温法通过测量火焰辐射光谱来实现温度的非接触在线测量,具有测温范围宽、响应快及可靠性高等优点,可应用于固体火箭发动机羽流温度测量。在此提出了基于火焰辐射光谱的固体火箭发动机羽流温度测量方法,采用350～1 000 nm波段光纤光谱仪搭建了发动机羽流火焰辐射光谱测量系统,利用标准辐射黑体炉开展光谱仪响应系数标定,获得响应系数随波长的变化曲线,并以此用作羽流辐射光谱数据修正。之后将该测量系统应用于标准Φ118固体火箭发动机地面试验,开展典型12%铝质量含量推进剂发动机羽流辐射光谱实验测量,选取不同时刻羽流辐射光谱分析了发动机羽流辐射光谱特征,并利用双色法灰性判断原理对羽流火焰灰体特性进行讨论,验证在675～745 nm波段发动机羽流火焰辐射可近似认为灰体,该波段辐射率随波长变化最大相对偏差为4.01%,相对均方差为1.53%。因此,基于普朗克辐射定律开展辐射光谱拟合参数获得不同时刻羽流温度与辐射率参数,并讨论测量结果与发动机工作状态的关系。最后,开展12%,15%与19%铝质量含量的不同推进剂配方固体火箭发动机羽流辐射光谱测量,将辐射光谱法温度测量值与理论热力计算值进行比较,两者最大偏差值为5.40%,讨论了不同铝含量推进剂发动机羽流辐射光谱特征,并结合温度与辐射率测量结果,分析了固体推进剂铝含量对辐射光谱、羽流温度及辐射率的影响。通过固体火箭发动机羽流辐射光谱测温方法研究,为固体火箭发动机性能评估及推进剂配方优化等研究提供了有效的羽流参数测量手段。分析获得的推进剂铝含量对发动机羽流辐射光谱、温度及辐射率参数的影响,为降低固体发动机羽流特征信号提供了重要的实验数据支撑。     

强耦合表面激子内部激发态的性质

采用线性组合算符和幺正变换方法,研究极性晶体中强耦合表面激子内部激发态的性质.计算了表面激子的激发态能量、激发能量和平均声子数.     

高速模型尾迹流场及其电磁散射特性相似性实验研究

高速目标再入大气层或在临近空间飞行时,空气电离形成的等离子体鞘套和尾迹对目标的雷达散射特性会产生影响.为了研究不同模型尾迹流场及其电磁散射特性规律和相似性,以氧化铝球模型为研究对象,在弹道靶设备上开展了双尺度参数相同的条件下高速球模型尾迹流场及其电磁散射相似性实验研究.由二级轻气炮发射模型,模型直径分别为8.0、10.0、12.0、15.0 mm,速度约6 km/s,靶室压力分别为6.3,5.0,4.2,3.3 k Pa,采用阴影照相系统测量模型激波脱体距离、电子密度测量系统测量模型尾迹的电子密度分布、X波段单站雷达系统测量在视角为40?的模型及流场的雷达散射截面(RCS)分布.实验结果表明:在速度不变、双尺度参数相同的条件下,随着模型尺寸的增加,激波脱体距离逐渐增加,激波脱体距离与模型直径之比近似相同;不同模型尾迹电子密度测量曲线的趋势和数量级一致,表明不同模型的尾迹流场适用于双缩尺律;不同尺寸模型尾迹的总体RCS与分布RCS均不相同,表明不同模型尾迹的电磁散射不适用于二元缩尺律;高速球模型全目标电磁散射能量分布在模型及其绕流区域、等离子体尾迹区域;高速球模型全目标电磁散射能量在模型及绕流场区域出现1个强散射中心,在模型湍流尾迹区域出现多个散射中心;高速球模型尾迹的RCS测量信号呈现随机性分布特性,幅度脉动和频率脉动均没有周期性;随着模型尺寸的增加,模型尾迹的总体RCS增加,尾迹脉动频率的变化范围减小.