窄禁带半导体材料中共振缺陷态测量

运用量子电容谱测量技术，在窄禁带半导体材料InSb和HgCdTe价带和导带中分别发现了两个共振缺陷态．根据建立的实验模型研究了这些共振缺陷态的特性 关键词：     

量子光学中的非经典态

本文扼要地介绍了光子数态、热光场态、相干态、压缩态、相位态和中间态等。重点是介绍它们的物理性质。例如,指出相干态在谐振子座标表象中的表示就是带电谐振子在均匀电场中的基态波函数;它的时间演化波包的概率密度分布,形状不随时间变但中心位置随时间作周期振荡。文中对相干态和压缩态等提供了也许是一点新的看法：将相干态、压缩真空态、压缩相干态和相干压缩态等看作是一准玻色子的基态或相干态。而实现的手段可以是原来的幺正算符也可以是投影算符。这样的好处是：（１）对相干态和压缩态间的联系有更深的认识;（２）便于计算和进一步展开等等。文中还对各个态的压缩性、统计性等作了介绍,有的还用图表等演示了它们的非类经典特性。最后,文中还介绍了准概率分布函数、相空间技术以及它们的应用并给出了示例     

量子光学中的非经典态

本文扼要地介绍了光子数态、热光场态、相干态、压缩态、相位态和中间态等。重点是介绍它们的物理性质。例如,指出相干态在谐振子座标表象中的表示就是带电谐振子在均匀电场中的基态波函数;它的时间演化波包的概率密度分布,形状不随时间变但中心位置随时间作周期振荡。文中对相干态和压缩态等提供了也许是一点新的看法：将相干态、压缩真空态、压缩相干态和相干压缩态等看作是一准玻色子的基态或相干态。而实现的手段可以是原来的幺正算符也可以是投影算符。这样的好处是：（１）对相干态和压缩态间的联系有更深的认识;（２）便于计算和进一步展开等等。文中还对各个态的压缩性、统计性等作了介绍,有的还用图表等演示了它们的非类经典特性。最后,文中还介绍了准概率分布函数、相空间技术以及它们的应用并给出了示例     

窄禁带光子晶体能态密度的研究

利用平面波展开法研究了窄禁带光子晶体材料的能态密度分布情况,得到了窄禁带材料构成的三角晶格光子晶体能态密度随着介电常数差值的增大而增大,并且分析了氮化镓在f=0.3时,能态密度分布最小,出现最大光子带隙。研究结果为窄禁带光子晶体器件的构造提供理论依据。     

偏振态对复周期光子晶体禁带的影响

对于一维复周期光子晶体,当制作用的波长满足一定条件时可以实现禁带的展宽,本文利用传输矩阵法数值计算了偏振态对折射率渐变的一维复周期全息光子晶体的禁带的影响。通过计算发现,制作波长不等的复周期结构光子晶体,随着再现光的照射角度增大,S偏振态下禁带出现分裂;P偏振态下禁带均可视作完整展宽,没有分裂现象。同一制作波长两次曝光制作的复周期结构,不论是P偏振还是S偏振,禁带均实现展宽而没有分裂。这一结果对实现一维全息光子晶体禁带展宽具有指导意义。     

缺陷层空心单模Bragg光纤的色散特性

针对空心单模Bragg光纤在1.55μm附近表现出非常大的正色散,研究了包层缺陷层对空心单模Bragg光纤色散的调节作用。利用光学软件FDTD Solutions对缺陷层空心单模Bragg光纤的模式耦合特性进行分析;对比分析普通空心单模Bragg光纤和缺陷层空心单模Bragg光纤的色散曲线;讨论了包层缺陷层结构参数对空心单模Bragg光纤的色散调节作用。     

体积全息图中的光子禁带

利用光子晶体的概念和方法分析光学全息,用光子晶体的带结构解释了体积全息图的性质.与超晶格不同,全息光子晶体的介电常量是渐变而不是突变的.着重讨论了一维非倾斜反射全息图在再现光不同角度入射情况下禁带结构的性质,通过基元反射全息实验的验证,证明体全息的禁带分析与实验结果符合得很好. 关键词： 体积全息图 光子晶体 禁带     

氢化非晶锗碳薄膜中的自旋缺陷态

本文应用原位电子自旋共振(ESR)技术研究了射频反应溅射法制备的氢化非晶锗碳(a-Ge_1-xC_x:H)薄膜中自旋缺陷态的种类、密度、温度依赖关系和热力学动态行为。在分解ESR谱的过程中,发现了它的不对称成分,并对此进行了定量分析和微观机理的探讨。 关键词：     

三组元声子晶体中的缺陷态

运用基于平面波的超元胞方法，研究作为缺陷引入的第三组元材料(四氯化碳、水)对二维二组元声子晶体(水/水银，四氯化碳/水银)带结构的影响.结果表明，二组元声子晶体在引入第三组元点缺陷/线缺陷后，在原来的带结构中会出现缺陷态/带，原带隙的位置、宽度变化不大；缺陷态/带频率主要受第三组元材料物性参数的影响；这些缺陷态都是局域化的.因此，在具有宽带隙的二组元体系中引入适当的第三组元点缺陷/线缺陷，让缺陷态/带频率落在二组元体系的带隙中，就可以形成特殊的滤声态/波导态.声子晶体的这一特性对于声波/弹性波的传播和新的声学应用具有重要意义. 关键词： 声子晶体 三组元 点缺陷 线缺陷     

周期变截面波导中的多缺陷态*

设计了一种具有对称结构的多缺陷周期变截面波导,并在其Bragg禁带中实现了多缺陷态的产生。研究表明,通过调整缺陷的个数和长度可实现对缺陷态数目的选择和缺陷态中心频率的调谐。另外,改变重复周期个数可对缺陷态的带宽进行调节。通过对各缺陷态的声场分布进一步分析,我们发现声压沿波导中心轴呈对称或反对称分布。对称缺陷态的最大声能量总是向长度较小的缺陷处偏移,而反对称缺陷态则相反,总是向长度较大的缺陷处偏移。利用这种偏移特性可实现对多缺陷态的声场调控。这不仅使我们对声缺陷态的认识更加深入,更有利于功能型声波导器件的发展与应用。     

二维周期性复合介质中声波带隙结构及其缺陷态

用平面波展开方法和超元胞方法,研究了钢柱体在水中按周期性排列时声波的能带结构.讨论了钢柱体的横截面形状(圆形和正方形)、柱体的体积填充率及缺陷等因素对声波带隙结构的影响. 关键词： 声波 带隙 缺陷态     

Influence of surface band gaps on the lifetimes of charge transfer states

Using a first principles electronic structure method, we investigate how a band gap in the surface projected density of states of a noble metal influences the resonant tunneling lifetime of an atomic level near the surface. Comparing Li atoms outside Cu(1 1 1), where the Li 2s level is within the gap, with Cu(0 0 1), where the Li 2s level is below the gap, reveals that the lifetime of the ionization level of Li is longer on Cu(1 1 1). This difference is caused both by the decreased final state phase space for the tunneling electron on Cu(1 1 1) and by a reduction in intra-atomic hybridization in Li outside a surface whose band gap encompasses the ionization level. Our results are consistent with previous experiments and theory that predict a similar trend for the ionization level of Cs above Cu(1 1 1) and Cu(0 0 1).     

Transverse wave band gaps and longitudinal wave band gaps in solid phononic crystals

Based on the properties of transverse (divergenceless) waves and longitudinal (irrotational) waves, we divided the transverse wave modes and longitudinal wave modes from the mixed eigen modes in solid phononic crystals. By investigating the transverse wave and longitudinal wave band structures at low frequency, we found that transverse bands and longitudinal bands exhibit different behaviors in solid systems including spherical scatterers. Phononic crystal with a large density ratio of solid spheres to the background can guarantee both the large longitudinal and large transverse band gap, but solid spheres with a small ratio of longitudinal wave velocity to transverse wave velocity can only help to enlarge the longitudinal band gap, and do not help to enlarge the transverse band gap.     

Uncoupled photonic band gaps

We theoretically investigated the symmetry properties of the modes in two-dimensional square lattice photonic crystals in order to study phenomena that would enable new frontiers in the applications of photonic crystals. Using group theory, symmetry analysis of the photonic crystals bands has been done. Particular attention was given to the search for the uncoupled B modes that cannot be excited by the external plane wave because they are symmetry forbidden. The existence of the uncoupled modes enabled to define new physics phenomena: uncoupled photonic band gaps. For the frequency ranges inside the uncoupled photonic band gaps, zero transmission is obtained. Therefore, there are two different types of photonic gaps in the photonic crystals: photonic band gaps and uncoupled photonic band gaps. The appearance of uncoupled photonic band gaps in photonic crystals could at least improve the application of the existing photonic materials and structures or even enable the usage of new ones for devices like waveguides, filters, and lasers.     

缺陷态对4340钢-环氧树脂二维声子晶体带隙的影响

采用平面波展开法及平面波超元胞法研究缺陷态对4340钢-环氧树脂二维声子晶体带隙的影响. 以环氧树脂作为基底,把正方形结构排列的4340钢均匀的插入基底中,计算完整晶体、45°线缺陷态晶体、90°线缺陷态晶体、135°线缺陷态晶体、180°线缺陷态晶体的带隙. 结果表明,缺陷态的带隙宽度与完整晶体的带隙宽度相比最大可增大约31倍;对于不同的缺陷结构在F=0.1-0.9的范围内均有带隙出现且随着缺陷态角度的增大. 同时讨论带隙数目N,最低带隙相对宽度Δω/ω_g与填充率F之间的关系. 关键词： 缺陷态 带隙宽度 带隙数目     

Entanglement sudden death in band gaps

Using the pseudomode method, we evaluate exactly time-dependent entanglement for two independent qubits, each coupled to a non-Markovian structured environment. Our results suggest a possible way to retard entanglement sudden death by modifying the qubit-pseudomode detuning and the spectrum of the reservoirs. Particularly, in environments structured by a model of a density-of-states gap which has two poles, entanglement trapping and prevention of entanglement sudden death occur in the weak-coupling regime.     

Bulk band gaps in divalent hexaborides

Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB6 additionally provide a stringent test case for many-body quasiparticle band calculations.     

可调光子晶体研究进展

可调光子晶体是光子晶体研究中的一个新领域，文章简单介绍了当前可调光子晶体的发展状况，阐述了其调制机理及存在的问题，同时论述了可调光子晶体的发展趋势。     

Two-dimensional absolute photonic band gaps in the visible

The most promising two-dimensional photonic crystals are the graphite lattice of dielectric rods in air background and the triangular lattice of air holes in dielectric background. In this paper, we compare their convenience in achieving structures which inhibit the propagation of visible electromagnetic waves. For visible waves, etching is difficult because the structure period must be smaller than the light wavelength. Furthermore, the semiconductor materials whose electronic band gap does not absorb any optical waves have little dielectric constant, which reduces photonic band gap widths. We show, using the Plane Wave Method and the Transfer Matrix Method, that the triangular structure is not appropriate because its gap is too narrow and its dimensions are too small for fabrication. On the other hand, wider gaps and larger dimensions that should be etched easily in wide gap semiconductors make graphite a much more suitable structure.