霍尔角、霍尔电场与载流子能态关系研究

讨论了霍尔电场和外加电场对裁流子作用问题,认为外电场既改变载流子在晶格势场中的能态,也驱动栽流子作漂移运动．在外电场作用下,霍尔角正切反映了载流子在晶格势场中增加的能量占外电场输入能量的百分比,外电场输入能量的其他部分转变成裁流子漂移运动动能、晶格格点热振动能量及焦耳热．     

耦合强度和磁场对光学极化子平均声子数的影响

应用线性组合算符和幺正变换方法,研究磁场和耦合强度对光学极化子平均声子数的影响.数值计算表明：当电子接近晶体表面时,趋于弱耦合极限,光学极化子的平均声子数为零;当电子远离晶体表面时,振动频率和平均声子数均与磁场强度及耦合参数有关,且随磁场强度和耦合参数的变化而变化.     

Coherent spin manipulation without magnetic fields in strained semiconductors

A consequence of relativity is that in the presence of an electric field, the spin and momentum states of an electron can be coupled; this is known as spin-orbit coupling. Such an interaction opens a pathway to the manipulation of electron spins within non-magnetic semiconductors, in the absence of applied magnetic fields. This interaction has implications for spin-based quantum information processing and spintronics, forming the basis of various device proposals. For example, the concept of spin field-effect transistors is based on spin precession due to the spin-orbit coupling. Most studies, however, focus on non-spin-selective electrical measurements in quantum structures. Here we report the direct measurement of coherent electron spin precession in zero magnetic field as the electrons drift in response to an applied electric field. We use ultrafast optical techniques to spatiotemporally resolve spin dynamics in strained gallium arsenide and indium gallium arsenide epitaxial layers. Unexpectedly, we observe spin splitting in these simple structures arising from strain in the semiconductor films. The observed effect provides a flexible approach for enabling electrical control over electron spins using strain engineering. Moreover, we exploit this strain-induced field to electrically drive spin resonance with Rabi frequencies of up to approximately 30 MHz.     

分子晶体环上的椭圆函数波

得到了环上的有色散项的分子晶体模型的椭圆函数波解．当环的周长趋于无穷大时，模型的椭圆函数波解回复于一维链的改进光学极化子解．计算了模型中自陷态的晶格位移和电子的自陷阱．     

二维极化子有效质量与温度的关系

本文计及晶格的原子结构讨论了极化晶体中二维极化子的性质。用二次量子化方法处理晶格振动及其与电子的相互作用,导出了二维极化子的自陷能和有效质量,给出了二维极化子有效质量与温度的关系。     

SVM-PSO混合算法的光学电压传感器内电场优化

对光学电压传感器内电场的优化多采用有限元计算结合穷举搜索,无法反映电场分布与传感结构参数之间的非线性映射关系,且计算与搜索费时、效率低,容易落入局部陷阱。提出基于支持向量机(SVM)与粒子群(PSO)的电场优化混合算法,通过PSO优化SVM的参数以建立电光晶体内电场分布的模型,再由PSO对模型求解得到最优电场分布。以介质包裹结构为例,构建包裹介质的介电常数、厚度以及长度与晶体内电场分布之间的非线性映射关系,且求解过程能够有效地避开局部陷阱,优化后晶体内电场均匀度提高了20.8%、训练时间节省了89%。最后通过实验验证了模型的有效性。     

The birth of a quasiparticle in silicon observed in time-frequency space

The concept of quasiparticles in solid-state physics is an extremely powerful tool for describing complex many-body phenomena in terms of single-particle excitations. Introducing a simple particle, such as an electron, hole or phonon, deforms a many-body system through its interactions with other particles. In this way, the added particle is 'dressed' or 'renormalized' by a self-energy cloud that describes the response of the many-body system, so forming a new entity--the quasiparticle. Using ultrafast laser techniques, it is possible to impulsively generate bare particles and observe their subsequent dressing by the many-body interactions (that is, quasiparticle formation) on the time and energy scales governed by the Heisenberg uncertainty principle. Here we describe the coherent response of silicon to excitation with a 10-femtosecond (10(-14) s) laser pulse. The optical pulse interacts with the sample by way of the complex second-order nonlinear susceptibility to generate a force on the lattice driving coherent phonon excitation. Transforming the transient reflectivity signal into frequency-time space reveals interference effects leading to the coherent phonon generation and subsequent dressing of the phonon by electron-hole pair excitations.     

格点能量变化时离散晶格中荷电粒子在任意含时电场作用下的运动

本文研究了当格点能量变化时一维键上的带电粒子在任意含时电场作用下的运动,给出了动量空间的普遍的形式解,并就静电场的情形讨论了粒子在动量空间的局域性问题.     

极性晶体板中极化子的基态能量和有效质量

应用Ｌｅｅ－Ｌｏｗ－Ｐｉｎｅｓ（ＬＬＰ）方法研究极性晶体板中极化子的性质,给出极化子基态能量和有效质量的解析表达式,并以ＧａＡｓ极性晶体板为例进行数值计算,讨论了体纵光学模声子和表面光学模声子对极化子性质的影响     

高能电子束的电光探测方法

本文介绍两种电光探测方法测量电子束长度：延迟扫描法、啁啾脉冲法(包括啁啾脉冲光谱仪法和啁啾脉冲互相关法)，并比较了不同方法的速度、时间分辨率．论文还讨论了使用电光晶体时吸收和色散对电子束电场形状的影响，及电子束与探测脉冲之间的同步问题．     

双模型三元混晶的界面极化子

采用ＥＰＭＡ近似法,研究了双模型三元混晶界面极化子的性质,计算了ＺｎＳｘＳｅ１－ｘ（ＧａＡｓ）和ＡｌＧａ１－ｘＡｓ（ＧａＳｂ）材料中界面光声子与电子的耦合随ｘ的变化。结果表明,在强电场作用下,界面光声子与电子的耦合加强;体光声子与电子的耦合在ｘ的某一值处存在极小值,界面光声子与电子的耦合随ｘ的变化则较复杂。     

量子阱中极化子的性质

给出声子分布函数的解析表达式，并利用该表达式和Lee-Low-Pines(LLP)变分方法计算极性晶体板中极化子的基态能量，与自恰的数值结果进行比较，结果吻合。     

电场对抛物量子线中强耦合极化子性质的影响

采用线性组合算符法和变分法研究了电场对抛物量子线中强耦合极化子性质的影响，在考虑电子与LO声子相互作用和加电场的情况下，计算了抛物量子线中强耦合极化子的基态能量．数值计算结果表明：抛物量子线中强耦合极化子的基态能量Eo随约束强度ω0的增强而增大，而随电场强度F和量子线长Z的增大而单调减小．     

晶体中束缚光学极化子的声子平均数

研究晶体中束缚极化子的性质，采用Tokuda改进的线性组合算符、Lagrange乘子和变分法讨论了晶体中强、弱耦合极化子的振动频率和光学声子平均数与拉格朗日乘子u的关系，以RbCl晶体为例进行了数值计算，结果表面：束缚极化子的振动频率，基态能量和声子平均数随拉格朗日乘子u的增加而增大。     

有限温度下极化子中的光学声子平均数

研究了在有限温度下极性晶体中与光学声子相互作用的体极化子的性质.采用么正变换和线性组合算符法导出了有限温度下,极性晶体中强、弱耦合电子周围光学声子的平均数.     

有局域场的三能级∧系统的瞬态解析结果

考虑Lorentz局域场效应的影响，我们在Liouville运动方程的基础上用微扰理论分析了一个三能级系统的非线性响应．在非线性光学响应中，两波矢分别为k1，k2的连续相干脉冲将会在新的方向产生新的光波．计算之后，我们给出四波混频信号关于Lorentz局域场因子l的表达式，发现负时间延迟时在2k2-k1方向仍有四波混频信号，四波混频信号的频率也有所改变．     

Electrical control of spin coherence in semiconductor nanostructures.

The processing of quantum information based on the electron spin degree of freedom requires fast and coherent manipulation of local spins. One approach is to provide spatially selective tuning of the spin splitting--which depends on the g-factor--by using magnetic fields, but this requires their precise control at reduced length scales. Alternative proposals employ electrical gating and spin engineering in semiconductor heterostructures involving materials with different g-factors. Here we show that spin coherence can be controlled in a specially designed AlxGa1-xAs quantum well in which the Al concentration x is gradually varied across the structure. Application of an electric field leads to a displacement of the electron wavefunction within the quantum well, and because the electron g-factor varies strongly with x, the spin splitting is therefore also changed. Using time-resolved optical techniques, we demonstrate gate-voltage-mediated control of coherent spin precession over a 13-GHz frequency range in a fixed magnetic field of 6 T, including complete suppression of precession, reversal of the sign of g, and operation up to room temperature.     

Attractive and repulsive Fermi polarons in two dimensions

The dynamics of a single impurity in an environment is a fundamental problem in many-body physics. In the solid state, a well known case is an impurity coupled to a bosonic bath (such as lattice vibrations); the impurity and its accompanying lattice distortion form a new entity, a polaron. This quasiparticle plays an important role in the spectral function of high-transition-temperature superconductors, as well as in colossal magnetoresistance in manganites. For impurities in a fermionic bath, studies have considered heavy or immobile impurities which exhibit Anderson's orthogonality catastrophe and the Kondo effect. More recently, mobile impurities have moved into the focus of research, and they have been found to form new quasiparticles known as Fermi polarons. The Fermi polaron problem constitutes the extreme, but conceptually simple, limit of two important quantum many-body problems: the crossover between a molecular Bose-Einstein condensate and a superfluid with BCS (Bardeen-Cooper-Schrieffer) pairing with spin-imbalance for attractive interactions, and Stoner's itinerant ferromagnetism for repulsive interactions. It has been proposed that such quantum phases (and other elusive exotic states) might become realizable in Fermi gases confined to two dimensions. Their stability and observability are intimately related to the theoretically debated properties of the Fermi polaron in a two-dimensional Fermi gas. Here we create and investigate Fermi polarons in a two-dimensional, spin-imbalanced Fermi gas, measuring their spectral function using momentum-resolved photoemission spectroscopy. For attractive interactions, we find evidence for a disputed pairing transition between polarons and tightly bound dimers, which provides insight into the elementary pairing mechanism of imbalanced, strongly coupled two-dimensional Fermi gases. Additionally, for repulsive interactions, we study novel quasiparticles--repulsive polarons--the lifetime of which determines the possibility of stabilizing repulsively interacting Fermi systems.     

TGS铁电相变的时域方法研究

利用时域方法在 TGS 单晶居里点附近以±0.001℃的恒温精度研究了铁电相变的过程,观察到驰豫机构可分为晶格和电子云畸变、电畴运动、和自发极化电偶极矩的屏蔽电荷的激发三种成分.介电损耗在10~(-3)—10~3Hz 频程的峰值表明,在铁电相变过程中晶体和外界的能量交换主要来自屏蔽电荷的激发.     

原子尺度上的波

提出全同粒子以及虚粒子假设,并推导了二维速度控制条件,再结合原子势函数,在原子尺度上描述了线性波的传播。考虑晶格非谐性以及位错的影响,进一步探究了二阶非线性波的产生机理。理论分析表明,晶格非谐性和位错引起的晶格畸变会诱发产生高阶虚粒子,高阶虚粒子是高阶非线性波产生的关键因素,位错等材料早期非线性或细微损伤导致高阶虚粒子增多而引发明显的高次谐波,因此,可以通过探测高次谐波诊断材料早期损伤。