Exciton spectra in SrS1−xSex mixed crystals

Exciton reflection spectra are investigated at 2 K on single crystals of SrS_1?xSe_x over the whole composition range. All the exciton reflection structures are found to show an amalgamation-type behaviour. From the observed dependence of the reflection peaks on composition and temperature, it is concluded that the exciton spectra of these Sr-chalcogenides are composed of two kinds of the exciton multiplets, the lower one being associated with the X-point band-edge and the higher one with the г-point band edge. It is predicted that these crystals have an indirect band-gap for which phonon-assisted dipole transitions are parity-forbidden.     

Photodetachment of H^- near a Partially Reflecting Surface-Ⅰ

Theoretical and interpretative study on the subject of photodetachment of H^- near a partially reflecting surface is presented, and the absorption effect of the surface is investigated on the total and differential cross sections using a theoretical imaging method. To understand the absorption effect, a reflection parameter K is introduced as a multiplicative factor to the outgoing detached-electron wave of H^- propagating towards the wall. The reflection parameter measures, how much electron wave would reflect from the surface; K = 0 corresponds to no reflection and K = 1 corresponds to the total reflection.     

New experimental evidence of the structural modification in single crystal Bi2Sr2CaCu2Oy by X-ray diffraction observation

The variations of the high angle 00 peak-shape by means of X-ray l scans of the 00l fundamental reflections were investigated in detail for a highly oriented Bi₂Sr₂CaCu₂O_y (Bi2212) crystal with sufficiently small intrinsic mosaicity and the same crystal annealed in air at 250, 300, 400, 600, and 750°C for 20 h in consequence. For the first time, we observed a new additional reflection almost overlapped original 00l fundamental reflection at annealing temperature below 400°C by X-ray diffraction measurement, which shows that there coexisted two sets of lattice periodicity in the c-direction of the annealed crystal. The new additional reflection appeared at 250°C and disappeared at 400°C. Its intensity was increased at 300°C. The measurements of the AC susceptibility, c-axis parameter and full width at half maximum (FWHM) of the 00 peaks showed that the new additional reflection was associated with the oxygen diffusion in CuO₂ planes and the changes of strain field. The results provide the new experimental evidence that the structural distortion is more sensitive to the oxygen diffusion in CuO₂ planes than to that in Bi–O layers.     

CdxHg1-xTe混晶的远红外反射光谱和多振子模型

在温度4.2—300K和波数15—450cm^-1范围内研究了x=0.18到0.45的不同组份的Cd_xHg_1-xTe样品的远红外反射光谱。实验观察到了类CdTe光学声子反射带的精细结构和低组份样品类HgTe反射带的复杂结构,研究了这些结构对组份和温度的关系,并用多振子模型讨论了反射光谱的这种精细结构。对实验反射光谱用经典的振子匹配方法进行了拟合计算,并从这种拟合运算获得了Cd_(x^-)Hg_1-xTe的远红外介电函数谱及其它光学常数和频率的关系。 关键词：     

Shrinkage of picosecond laser beam by plasma reflection in super-resolution near-field structure of SiN/Sb/SiN thin film

The transmittive and reflective Z-scan technique is used with a 10 Hz, frequency doubled, Q-switched, and mode-locked Nd:YAG laser to verify that the reflectivity of the super-resolution near-field structure of an SiN/Sb/SiN thin film increases as incident intensity decreases. This intensity-dependent reflection, called nonlinear reflection, reflects a TEM(00) mode laser beam more strongly at its periphery than at its center and so shrinks the transmitted laser beam. The observed nonlinear reflection is attributed to laser-induced change of carrier densities in Sb, to justify quantitatively the experimental results.     

Reflection of structural waves at a solid/liquid interface

This paper investigates the reflection characteristics of structural or guided waves in rods at a solid/liquid interface. Structural waves, whose wavelengths are much larger than the diameter of the rod, are described in a first approximation by classical one-dimensional wave theory. The reflection characteristics of such waves at a solid/liquid (melting) interface has been reported by two different ultrasonic measurement techniques: first, measuring the fast regression rate of a melting interface during the burning of metal rod samples in an oxygen-enriched environment, and second, monitoring the propagation of the solid/liquid interface during the slow melting and solidification of a rod sample in a furnace. The second work clearly shows that the major reflection occurs from the solid/liquid interface and not the liquid/gas interface as predicted by plane longitudinal wave reflectivity theory. The present work confirms this observation by reporting on the results of some specially designed experiments to identify the main interface of reflection for structural waves in rods. Hence, it helps in explaining the fundamental discrepancy between the reflection characteristics at a solid/liquid interface between low frequency structural waves and high frequency bulk waves, and confirms that the detected echo within a burning metallic rod clearly represents a reflection from the solid/liquid interface.     

拓扑绝缘体基铁磁/f-波超导隧道结Andreev反射研究

基于Bogoliubov-de Gennes方程和Blonder-Tinkham-Klapwijk理论研究了三维拓扑绝缘体基铁磁/各向异性f-波超导隧道结的Andreev反射,其中f-波超导体选取f₁和f₂-波两种配对势.研究发现,对于f₁和f₂波,铁磁体中的磁能隙可以增强传统的Andreev逆向反射,但对Andreev镜面反射有抑制作用;但随着施加在超导体顶部电极上的栅极电位的增加,两种类型的反射都会增强.通过改变磁能隙,可以调节两种反射在准粒子输运过程中占有优势的程度.这些结果提供了一种实验检测拓扑绝缘体薄膜中镜面Andreev反射的方法.此外,隧穿电导和散粒噪声谱的差异可用于区分f₁和f₂波配对势.     

氢、氘和氚离子在固体表面上的反射

本文应用最近发展的离子输运双群模型计算了氢,氘和氚离子在固体表面的反射系数。与有关的实验资料和Monte-Carlo计算比较表明,双群模型所取得的结果是合理的、可用的。同时也表明了双群模型有可能成为研究离子在固体表面反射的有效的理论方法。 关键词：     

Long-wavelength IR spectroscopy of ZnTe/CdTe superlattices with quantum dots

This paper reports on the results of investigations of the lattice IR reflection spectra of ZnTe/CdTe multilayer superlattices with CdTe quantum dots grown by molecular-beam epitaxy on a GaAs substrate with a CdTe buffer layer. It is found that the lattice IR reflection spectra of the studied structures exhibit three intense bands associated with vibrational excitations in the GaAs substrate, ZnTe barriers separating the layers with CdTe quantum dots, and the CdTe buffer layer. An analysis of the reflection bands and shifts in the phonon frequencies has revealed internal elastic stresses both in the surface layer of the GaAs substrate and in the ZnTe barriers. It is established that elastic stresses undergo relaxation in the separating ZnTe layers with an increase in their thickness. An additional mode observed in the reflection spectra is explained by manifestations of ZnTe-like vibrations in the ZnCdTe alloy due to interdiffusion of Cd and Zn at the interfaces.     

1/R居中Cantor分形势垒的反射系数

提出描述微观粒子在分形势垒传播行为的干涉矩阵,利用分形势垒的自相似性及对称性导出计算1/R居中Cantor分形势垒总干涉矩阵的矩阵迭代关系,在不同的势垒高度V0和参数R下,计算了该分形势垒的反射系数,结果表明,其反射谱具有分形的自相似特性,这一研究成果可望在其它领域中得到应用     

The reflection of bounded inhomogeneous waves on a liquid/solid interface

Fourier analysis and normal mode theory are used to describe the reflection of bounded inhomogeneous waves on a liquid/solid interface. Nonspecular reflection phenomena in the Rayleigh angle are studied in detail. In this way, an explanation is given for the Rayleigh dip phenomenon for positive inhomogeneity factors and the related result of a reflection coefficient larger than unity when the sign of the inhomogeneity factor is reversed. In the limit of large beamwidths, the reflection coefficient predicted by the infinite plane inhomogeneous wave theory is obtained. These results are entirely consistent with the experimental work published by Deschamps [J. Acoust. Soc. Am. 96, 2841-2848 (1994)]. The energy efficiency of Rayleigh wave excitation is investigated as well. It is shown that for large beamwidths, the energy efficiency for bounded inhomogeneous waves is considerably higher in comparison with Gaussian and square-profiled beams.     

Model design on calculations of microwave permeability and permittivity of Fe/SiO2 particles with core/shell structure

Fe/SiO₂ particles with core/shell structure were prepared by coating silica on the surface of a commercial spherical carbonyl iron via the hydrolysis process of tetraethyl orthosilicate (TEOS). The electromagnetic performance of commercial carbonyl iron and as-prepared Fe/SiO₂ particles was studied theoretically and experimentally. As predicted by the theoretical calculation based on the Bruggeman formula and the Landau–Lifshitz–Gilbert (LLG) theory, the insulating surface layer of silica was effective to reduce the permittivity parameters of pure carbonyl iron. The measured results showed good agreement with the theoretical prediction. Although there was a little decrease in the permeability of the Fe/SiO₂ core/shell particles, a better impedance match especially at higher frequency range was obtained when used as a microwave absorber. The reflection loss (RL) curves show that the lowest reflection loss of Fe/Epoxy composite (−20.5 GHz) was obtained corresponding to the frequency of 8.5 GHz when the thickness of the absorber was 3 mm. A different trend was observed in Fe/SiO₂/Epoxy composite. The reflection loss value got lower by decreasing the thickness of absorbers. At the thickness of 2.2 mm, a relative low reflection loss (−17 GHz) corresponding to the frequency of 13.6 GHz was obtained. Compared with the Fe/Epoxy composite, the improvement on shifting the reflection loss peak to higher frequency and on reducing the optimal thickness of absorbers was made by Fe/SiO₂/Epoxy composite.     

Effect of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/superconductor contact

The Andreev reflection probability for a ferromagnet/isolator/superconductor (FIS) contact at the arbitrary spin-dependent amplitudes of the electron waves transmitted through and reflected from the potential barrier is found. It is shown that the Andreev reflection probabilities of electron and hole excitations in the FIS contact are different. The energy levels of the Andreev bound states are found. The ballistic conductance of the point FIS contact is calculated. The text was submitted by the author in English.     

Optical spectra and energy band structure of AgAsS2 crystals

Ground and excited states of three exciton series are observed in the region of fundamental absorption edge of AgAsS₂ crystals. The contours of exciton reflection spectra are calculated and the main parameters of excitons and energy bands are determined in the center of Brillouin zone. The optical reflection spectra are investigated at 30 K in E∥c and E⊥c polarizations in AgAsS₂ crystals in the region of 2-6 eV. The optical functions are calculated from the reflection spectra and a scheme of electronic transitions responsible for peculiarities of reflection spectra deep into the absorption band is proposed.     

Optical properties of hybrid periodic/quasiregular dielectric multilayers

Optical properties like transmission, omnidirectional reflection and localization of modes are theoretically investigated in hybrid periodic/quasiregular dielectric heterostructures based on porous silicon. It is shown that the fabrication of this class of multilayers would lead to an improvement of the formation of microcavities, the widening of the incidence angular interval for total reflection as well as the appearance of spatial localization of electric field intensity within specific regions of the structures.     

Enhancement of high PT hadrons due to collapsing Z(3) walls in heavy-ion collisions

We discuss enhancement of multiplicities of hadrons at high transverse momentum due to multiple reflections of quarks from collapsing Z(3) interfaces in the QGP produced in relativistic heavy-ion collisions. By modeling the dependence of effective mass of the quarks on the Polyakov loop order parameter, we evaluate the reflection coefficient of quarks from collapsing Z(3) interfaces. We use the effective potential proposed by Pisarski for the Polyakov loop to determine the profile of the Z(3) interfaces and calculate the reflection probability for quarks. We discuss the formation of a network of these Z(3) walls in relativistic heavy-ion collisions, in the QGP phase. We do a numerical simulation to calculate the modifications in the thermal transverse momentum spectra of the quarks/anti-quarks that results from a collapsing wall. We then use the recombination model to calculate the transverse momentum spectrum of final hadrons. Our results show enhancement of high P _T hadrons, with the enhancement being stronger for heavier quarks. Further, we find that due to larger reflection coefficient for heavier quarks, the density of strange and charm quarks/anti-quarks increases inside the collapsing walls. This implies enhancement in the multiplicities of multi-strange and multi-charmed hadrons.     

Absorption edge and optical constants of Tl2Ga2S3Se crystals from reflection and transmission,and ellipsometric measurements

The optical properties of Tl₂Ga₂S₃Se layered crystalline semiconductors were investigated from transmission, reflection and ellipsometric measurements. The experimental results of the room temperature transmission and reflection measurements performed in the wavelength range of 400–1100 nm showed the presence of both indirect and direct transitions in the band structure of the crystals with 2.38 and 2.62 eV band gap energies.     

Spin transport properties in ferromagnet/superconductor junctions on topological insulator

The spin-dependent Andreev reflection is investigated theoretically by analyzing the electronic transport in a thin-film topological insulator (TI) ferromagnet/superconductor (FM/SC) junction. The tunneling conductance and shot noise are calculated based on the Dirac-Bogoliubov-de Gennes equation and Blonder-Tinkham-Klapwijk theory. It is found that the magnetic gap in ferromagnet can enhance the Andreev retro-reflection but suppress the specular Andreev reflection. The gate potential applied to the electrode on top of superconductor can enhance the two types of reflections. There is a transition between the two types of reflections at which both the tunneling conductance and differential shot noise become zero. These results provide a method to realize and detect experimentally the intra-band specular Andreev reflection in thin film TI-based FM/SC structures.     

Spin-dependent transparency of ferromagnet/superconductor interfaces

We combine parameter-free calculations of the transmission and reflection matrices for clean and dirty interfaces with a scattering-theory formulation of Andreev reflection (AR) generalized to spin-polarized systems in order to critically evaluate the use of an extended Blonder-Tinkham-Klapwijk (BTK) model to extract values of the spin polarization for ferromagnetic metals from measurements of point-contact AR. Excellent agreement with the experimental conductance data is found for Pb/Cu but it is less good for Pb/Ni and poor for Pb/Co, indicating that the BTK formalism does not describe transport through superconducting/ferromagnetic interfaces correctly.     

基于飞秒瞬态反射/透射技术的纳米Au半透膜热效应研究

以飞秒激光放大器作为光源联合使用瞬态反射/透射实验技术研究了纳米Au半透明纳米薄膜中非平衡载能粒子的热传导过程. 在相同实验条件下, 发现该薄膜的瞬态透射和反射信号明显不同并且延迟时间在5.0–7.5 ps时瞬态透射信号的符号发生改变. 对纳米薄膜的透射和反射信号进行了对比分析, 分别使用双温模型和Crude近似进行数据模拟并拟合, 分析认为沿膜厚方向的温度梯度变化和界面热阻效应引起介电函数的变化不同, 从而引起了瞬态透射信号和反射信号的不同. 对于半透明金属纳米薄膜需要同时考虑其瞬态透射和反射影响才能得到准确的瞬态吸收结果. 随着抽运脉冲能量的增加, 可以看到上升时间约为1.0 ps, 电子-晶格弛豫时间增加.