二维复式声子晶体中基元配置对声学能带结构的影响

研究了二维复式声子晶体中基元配置对其声学能带结构的影响,发现当声子晶体的基元配置改变时,声子晶体的不可约布里渊区也会改变,而且部分能带的极值不再在高对称线上.特别地,在某些基元配置下,不可约布里渊区扩大为整个第一布里渊区.因此,对于对称性较高的复式晶格声子晶体,可用通常的方法得到能带结构,而对于对称性较低的复式晶格结构声子晶体,只有采用对整个第一布里渊区进行研究的方法,才能获得可信的能带结构及带隙.     

液封坩埚下降法生长非掺杂InP单晶的特性研究

用液封坩埚下降（ＬＥ－ＶＢ）法沿〈１００〉晶向成功地生长了非掺杂ＩｎＰ单晶．ＬＥ－ＶＢ晶体的４．２Ｋ光致发光谱包含束缚于中性浅受主上的激子发光、与Ｚｎ受主相关的施主－受主（ＤＡ）对发光及其声子伴线、以及与本征缺陷等有关的深能级发光三部分．通过与液封直拉（ＬＥＣ）生长的籽晶的光致发光谱比较表明，在ＬＥ－ＶＢ晶体中，束缚于中性浅受主上的激子发光与籽晶中的相差不大；ＤＡ对发光的晶格弛豫比籽晶中的小；与本征缺陷等有关的深能级发光强度比籽晶中的弱．晶体的室温光致发光谱仅包含带—带发光，其发光强度形貌测试结果表明，ＬＥ－ＶＢ晶体的带—带发光强度比ＬＥＣ籽晶的强．用Ｈｕｂｅｒ法对晶片腐蚀的结果表明，在ＬＥ－ＢＶ晶体中，位错密度仅为ＬＥＣ籽晶中的三分之一．分析认为，在ＬＥ－ＶＢ晶体中，本征缺陷和位错等浓度较低，可能是其带—带发光强度比在ＬＥＣ籽晶中强的物理起因．     

量子力学中的微扰变分法

本文介绍了量子力学中将微扰法和变分法结合起来考虑的微扰变分法，该方法可以同时兼有两种近似方法的优点．而且，由变分法求得的ψ－ｋ～（１）即可求能量二三级修正Ｅ－ｋ～（２）和Ｅ－ｋ～（３），由ψ－ｋ～（２）可求得四五级修正Ｅ－ｋ～（４）和Ｅ－ｋ～（５），如此等等．     

用X射线旋进照相观察Bi_（2＋x）Sr_（2－x）CuO_y晶体的调制结构

本文中我们用Ｘ射线旋进照相观察了Ｂｉ２＋ｘＳｒ２－ｘＣｕＯｙ的晶体调制结构．实验结果表明ｘ＝０．２的单晶样品具有单斜对称性，其空间群为Ｂ２／ｂ（或Ｂｂ）．随着ｘ的增加，单斜畸变减小．我们测量了调制波矢随名义组成的变化规律，讨论了调制波矢在第一布里渊区的对称性质．对调制结构提出了几种可能的有公度模型．最后讨论了调制结构对超导电性的影响．     

Ln(Ⅲ)-Ni(Ⅱ)与双水杨醛缩乙二胺席夫碱异核配合物的合成与波谱

合成了双水杨醛缩乙二胺席夫碱（ＳＡＬＥＮ）与镍的配合物Ｎｉ３（ＳＡＬＥＮ）２（ＮＯ３）６·Ｈ２Ｏ及镧系镍的异核配合物Ｌｎ２Ｎｉ３（ＳＡＬＥＮ）６（ＮＯ３）１２·Ｈ２Ｏ（Ｌｎ＝Ｌａ，Ｎｄ，Ｓｍ，Ｇｄ，Ｙｂ，Ｙ）．以紫外、红外光谱、磁化率，特别是１ＨＮＭＲ及ＥＰＲ波谱等方法研究了它们在组成、结构和配位等方面的异同．ＧｄＮｉＳＡＬＥＮ配合物的ＥＰＲ谱表明其在低温ＴＨＦ中呈“单峰效应”．文中讨论了配合物在不同溶剂中峰宽的相对关系、配合物晶体场强度及Ｇｄ３＋周围局部对称性问题     

二维电介质光子晶体中量子自旋与谷霍尔效应共存的研究

基于量子自旋霍尔或谷霍尔效应的拓扑光子结构具有对缺陷免疫和抑制背向散射的特性,对设计新型低损耗的光子器件起到了关键作用.本文巧妙设计了一种具有时间反演对称性的二维电介质光子晶体,实现了量子自旋霍尔效应和量子谷霍尔效应的共存.首先基于蜂巢结构排布的硅柱经过收缩扩张,打开了布里渊区Γ点的四重简并点形成拓扑平庸或非平庸的光子带隙,实现量子自旋霍尔效应.经过扩张后的蜂巢晶格演化成为Kagome结构,之后在Kagome晶格中加入正负扰动,打破光子晶体的空间反演对称性,导致布里渊区的非等价谷K和K′的简并点打开并出现完整带隙,实现了量子谷霍尔效应.数值计算结果表明,由拓扑平庸与非平庸、正扰动与负扰动的光子晶体组成的界面上可实现单向传输且对弯曲免疫的拓扑边缘态.最后,设计了基于两种效应共存的四通道系统,此系统为光学编码与稳健信号传输提供潜在方法,为电磁波的操纵提供了更大的灵活性.     

金M带谱时空特性测量

给出了金Ｍ带发射的空间尺度和时间尺度。用晶体配软Ｘ光条纹相机测得三倍频激光与金平面靶相互作用金Ｍ带发射的时间尺度：ＥＬ＝４６Ｊ，τ＝５７１ｐｓ时，金Ｍ带发射持续时间（ＦＷＨＭ）～８５０ｐｓ。用狭缝配晶体谱仪测得金Ｍ带发射的空间尺度：λ＝１．０６μｍ，ＥＬ＝１０６Ｊ，τ＝５５０ｐｓ时，金Ｍ带发射的空间尺度（ＦＷＨＭ）为５７μｍ；λ＝０．３５μｍ，ＥＬ＝２５～３８Ｊ，τ＝４８０～５７０ｐｓ时，金Ｍ带发射的空间尺度（ＦＷＨＭ）为２７～３９μｍ。     

关于Bose-Einstein凝聚(续)

关于Ｂｏｓｅ－Ｅｉｎｓｔｅｉｎ凝聚（续）张礼（清华大学现代应用物理系，北京１０００８４）（收稿日期：１９９７－０７－１６）４弱相互作用Ｂｏｓｅ气体：均匀凝聚体ＢＥＣ所以在粒子没有相互作用时发生，是全同玻色子体系波函数对称性的后果．在这个意义上可以称之...     

四氢呋喃（THF）非共振拉曼光谱中反对称散射的贡献

研究了四氢呋喃（ＴＨＦ）非共振拉曼光谱中反对称散射的贡献。在测量ＴＨＦ的非共振拉曼带的退偏比时发现，准转动式环折迭振动带及其组合带υ１６和υ１７虽是全对称振型，但其退偏比ρ约０．７５，远大于其它普通全对称振动带的退偏比。从时间反演对称性和空间对称性分析证明，反对称极化率张量不为零，进一步估计其大小比对称部分小一个量级（或同量级）。反对称散射的重要贡献是υ１６、υ１７振动带大退偏比的重要原因。     

二维排列共振吸收介质的光学特性研究

从理论上提出了一种二维排列的共振吸收介质阵列，计算了介质阵列的透射、反射与吸收光谱，发现存在着类似一维主动光子晶体中的共振光子带隙，并且这种结构的布里渊区边界点与二维阵列中原子之间的频率共振是产生这种共振带隙的必要条件. 本文还进一步分析了光子带隙与结构参数、二维阵列中原子共振中心以及吸收线宽之间的依赖关系. 关键词： 二维共振吸收介质阵列 布里渊区 光子晶体     

布里渊区中的对称平均点

本文提出了一些布里渊区中的对称平均点,用它可以方便地计算布里渊区中的平均值,其精度可以和特殊点相比而计算量却要小得多。文内给出了立方和六角晶格的对称平均点,并用具体的数值计算例子说明了它的计算精度。 关键词：     

二维光子晶体点群对称对不可约布里渊区的影响

采用平面波展开法,研究了二维光子晶体点群对称对不可约布里渊区的影响。在单柱体二维光子晶体单胞中增加一个柱体,设计成不同点群对称操作数的对称结构,计算了最低5条能带的本征频率值在第一布里渊区的分布图。结果表明:在计算二维光子晶体的能带结构时,如果光子晶体的点群对称操作数为n,所取的不可约布里渊区应为整个第一布里渊区的1/n。     

D_（6h）~1结构空间群C－G系数的计算

在晶体拉曼散射张量的计算中，晶体空间群的Ｃ－Ｇ系数具有重要作用，本文利用本征函数法~［１］，计算了一大类光学材料的结构空间群的Ｃ－Ｇ系数，同时给出波矢选择定则和Ｃ－Ｇ序列。     

Angle-resolved photoemission from Fe(110): Determination of E()

Using angle-resolved photoemission spectroscopy utilizing polarized synchrotron radiation with a clean Fe(110) sample, we identified each of the Σ₁-, Σ₃- and Σ₄-band peaks with certainty using symmetry selection rules. We also determined energy band dispersion along the γ-Σ-N direction in the bulk Brillouin zone assuming direct transitions. There are small discrepancies between the observed bands and recent ground-state band calculations possibly due to Coulomb correlation effects. A surface state with odd symmetry about the [001] crystal direction and a binding energy of 0.15 eV at γ in the surface Brillouin zone was observed. Our results show that the ground-state calculations of ferromagnetic iron based on the local exchange correlation potential are basically in agreement with experimental dispersion relationship measurements.     

Experimental band structure of GaSe obtained by angular resolved photoemission

A very detailed experimental band structure of the layered compound GaSe has been obtained in all the symmetry directions of the Brillouin zone for photon energy varying between 21 and 45 eV. It is shown that in this energy range the dispersion curves E (K//) are independent of the final state and that it is also possible, assuming a free electron like conduction band, to have information along the normal to the layers.     

Tunable reducibility of Brillouin zone and bandgap width in elliptical nanowire arrays

Rotating elliptical nanowire arrays as two-dimensional photonic crystals has been proposed and studied in this Letter. The analysis of the four lowest energy bands and the first bandgap width of some examples illustrates that the rotation and configuration of the primitive cell can have effects on the reducibility of the Brillouin zone.As the central element's orientation changes, the irreducible Brillouin zone could be expanded to the whole first Brillouin zone. Special attention has been paid to the nanowire arrays with adjacent elements perpendicular to each other, and the irreducible Brillouin zone unexpectedly retracted back to the 1/8 of the first Brillouin zone though the symmetry of elements is lower than that of the square lattice. Meanwhile, the first bandgap width of the perpendicular array can be adjusted by the rotation of each primitive element.     

One-Fe versus two-Fe Brillouin zone of Fe-based superconductors: creation of the electron pockets by translational symmetry breaking

We investigate the physical effects of translational symmetry breaking in Fe-based high-temperature superconductors due to alternating anion positions. In the representative parent compounds, including the newly discovered Fe-vacancy-ordered K(0.8)Fe(1.6)Se(2), an unusual change of orbital character is found across the one-Fe Brillouin zone upon unfolding the first-principles band structure and Fermi surfaces, suggesting that covering a larger one-Fe Brillouin zone is necessary in experiments. Most significantly, the electron pockets (critical to the magnetism and superconductivity) are found only created with broken symmetry, advocating strongly its full inclusion in future studies, particularly on the debated nodal structures of the superconducting order parameter.     

Anisotropic photonic crystals: Generalized plane wave method and dispersion symmetry properties

This article presents a generalized vector plane wave expansion method, applicable to isotropic and anisotropic periodic dielectric media of arbitrary geometry and dimension. The influence of anisotropic material orientation on the symmetry properties of photonic crystal dispersion surface is discussed. It is shown that the overall Brillouin zone symmetry is formed by the intersection of the photonic crystal lattice symmetry and the symmetry determined by the anisotropic material orientation. This work explains how to define the irreducible Brillouin zone of a two-dimensional anisotropic photonic crystal and demonstrates that doing it correctly allows one to avoid erroneous results, when calculating band gap diagrams of anisotropic photonic crystals. With the help of the methods presented, the possibility of controlling the band gaps of anisotropic photonic crystals by means of external electric field is shown.     

D_(6h)~4结构空间群C-G系数的计算

在晶体拉曼散射张量的计算中 ,晶体空间群的C G系数具有重要作用 ,本文利用本征函数法[1] ,计算了六角密排结构D46h空间群的C G系数 ,同时给出波矢选择规则和C G序列。     

Band diagram of spin waves in a two-dimensional magnonic crystal

The dispersion curves of collective spin-wave excitations in a magnonic crystal consisting of a square array of interacting saturated nanodisks have been measured by Brillouin light scattering along the four principal directions of the first Brillouin zone. The experimental data are successfully compared to calculations of the band diagram and of the Brillouin light scattering cross section, performed through the dynamical matrix method extended to include the dipolar interaction between the disks. We found that the fourfold symmetry of the geometrical lattice is reduced by the application of the external field and therefore equivalent directions of the first Brillouin zone are characterized by different dispersion relations of collective spin waves. The dispersion relations are explained through the introduction of a bidimensional effective wave vector that characterizes each mode in this magnonic metamaterial.