Effect of Electron Correlation on Phonon Spectra in Cuprates

We examine theoretically the phonon dynamics in the electron-phonon-coupled systems. The model Hamiltonian is a one-dimensional Hubbard model where the hopping of electrons induces the electron-phonon coupling. The numerically exact diagonalization of the Hamiltonian with truncation of the total number of phonons is performed. We calculate the phonon excitation spectra and find that the softening of phonons occurs in insulating case, and a diffusive character appears in the metallic case. We also calculate the charge and spin excitation spectra and find that the dynamics of the phonon coupled with the hopping of electrons is affected by the low energy charge and spin excitations.     

Dependence of Bessel Beam Characteristics on Angular Spectrum Phase Variations

Abstract

The Bessel beam propagation characteristics are investigated in the presence of azimuthally dependent phase variations of its angular components. The phase variations influence the beam symmetry and strongly reduce an axial intensity. An experimental interpretation of presented results is also discussed.     

Size Effect in the High-Field Magnetoconductivity of Pure Metal Single Crystals

The magnetoresistivity of tungsten single crystals with a residual resistivity ratio of up to 70,000 was measured in the temperature range from 4.2 to 55 K in a magnetic field of 10 T. The size effect, i.e., the linear dependence of the magnetoconductivity on the inverse sample dimensions, has been observed in the high-field magnetoconductivity. The experiments show that this phenomenon can be used to separate and study the surface and volume contributions to the magnetoresistivity of pure single crystals of compensated metals from liquid helium temperature up to approximately 25 K. It is shown that the specular reflection coefficient of the conduction electrons for pure metals in high magnetic fields can be determined in this way.     

Angular Dependence of the Radiation Power of a Josephson STAR-emitter

We calculate the angular dependence of the power of stimulated terahertz amplified radiation (STAR) emitted from a dc voltage applied across a stack of intrinsic Josephson junctions. During coherent emission, we assume that a spatially uniform ac Josephson current density in the stack acts as a surface electric current density antenna source, and the cavity features of the stack are contained in a magnetic surface current density source. A superconducting substrate acts as a perfect magnetic conductor with H _||,ac=0 on its surface. The combined results agree very well with recent experimental observations. Existing Bi₂Sr₂CaCu₂O_8+δ crystals atop perfect electric conductors could have Josephson STAR-emitter power in excess of 5 mW, acceptable for many device applications.     

Angular Dependence of Critical Currents in Silver-Sheathed Tl-1223 Tapes

Experimental results on the angular dependence of the critical current densities in silver-sheathed Tl-1223 tapes are presented.We show, that the improved texture of the Tl-based tapes leads to a better fit of the angular dependence of the critical current density J_c to the 2D-model. Deviations are found at very low magnetic fields, where the crystallographic misalignment of the tape structure becomes dominant. We observe a rapid decay of J_c with magnetic field, which implies weak-link dominated current transport. Both the angular and the magnetic field dependence of J_c are measured on fluorine-free and fluorine-containing samples.     

超短电子脉冲展宽的外场依赖性分析

根据已有文献研究结果,建立了Boersch效应电子脉冲展宽物理分析模型,确立了以时间弥散特征参量为核心参数的电子脉冲展宽表征理论,以此为基础分析了超短电子脉冲展宽对外场的依赖性.结果表明:相比匀速漂移场,加速场具有较好的抑制电子脉冲展宽作用,而减速场则增大了电子脉冲展宽;对条纹相机和超快电子衍射仪等电子枪系统而言,除了已知的两个区域一光阴极附近和偏转板后等电位漂移空间之外,光电子脉冲从高电位向低电位传输时其时间弥散也是非常显著的.此结论对高性能电子枪工程设计具有重要的理论指导价值.     

Angular Dependence of the Activation Energy in YBCO/PBCO Multilayers

The activation energy in several (YBCO) _m /(PBCO) _n superconducting multilayers was deduced from resistivity measurements in magnetic fields up to 16 T, as a function of the angle between the magnetic field and the ab planes. The activation energy U ₀ (B,) scales with a reduced field B _red =B(sin ² +cos ² / ² ) ^1/2 , with an angle dependent anisotropy parameter . A crossover from U ₀ log B _red , at low B _red , to U ₀ (B _red ) at high B _red , is also observed. The implications of these results on vortex dynamics and on the coupling between the superconducting layers will be discussed.     

Magnetic Field Angular Dependence of Magnetization Loss in ReBCO Superconducting Tapes

In the applications of high-temperature superconductors (HTS), the HTS tapes are usually exposed to the external magnetic field with different orientations. The critical current and AC loss are affected by both the field amplitude and field angles due to the anisotropy of HTS tapes. In this work, we first introduce the experimental system to measure the magnetization loss in HTS tapes based on the calibration-free method. Then, we present the magnetization loss results in 4.8-mm-wide AMSC wire, 4-mm-wide SuperPower wire, 4-mm-wide SuNam wire, and 10-mm-wide Fujikura wire in a perpendicular applied field at 77 K. The field amplitude is up to 100 mT, and the frequency varies from 44.2 to 87.1 Hz. We also present the magnetization loss in AMSC wire, SuperPower wire, SuNam wire, and Fujikura wire at different field angles. The field angle varies from 10 to 90 ^° in 10 ^° steps. The loss reduction with the decreasing of the field angle shows the anisotropic property of HTS tapes. We finally plot the measured magnetization loss of the samples as a function of the magnetic field amplitude normalized by the field angle to verify an empirical formula.     

光泵氦磁强计共振信号的角相关性

本文推导了应用圆偏振光时光泵诀磁强计共振信号的角相关性，Sθ＝Kycos^4θ,并与前得的到的应用自然光时共振信号的角相关性，Sθ＝Kx(3cos^2θ-1)^1作了比较，它们是光泵角度仪的理论基础。     

Beam Current Dependence of SEM Electron Probe Diameter

A method has been developed for measuring the dependence of the electron probe diameter d in a scanning electron microscope SEM on the beam current J. The relationship for the CAMSCAN CS-44 SEM is d(J) ~ J ^1/4, whereas electron probe formation theory gives d(J) ~ J ^3/8; the reasons for these differences are considered.     

Dependence of Electron Density on Fermi Energy in N-Type Gallium Antimonide

The majority electron density as a function of the Fermi energy is calculated in zinc blende, n-type GaSb for donor densities between 10¹⁶ cm⁻³ and 10¹⁹ cm⁻³. These calculations solve the charge neutrality equation self-consistently for a four-band model (three conduction sub-bands at Γ, L, and X and one equivalent valence band at Γ) of GaSb. Our calculations assume parabolic densities of states and thus do not treat the density-of-states modifications due to high concentrations of dopants, many body effects, and non-parabolicity of the bands. Even with these assumptions, the results are important for interpreting optical measurements such as Raman measurements that are proposed as a nondestructive method for wafer acceptance tests.     

Dependence of Mechanical and Thermal Properties of Thermoplastic Composites on Electron Beam Irradiation

Since the restrictions for environmental protection being strengthened, thermoplastics reinforced with natural fibers (NF’s), such as jute, kenaf, flax, etc. have appeared as alternatives to chemical plastics for automobile interior materials. In this study, the thermal conductivity, tensile strength, and deformation of several kinds of thermoplastic composites composed of 50% polypropylene (PP) and 50% natural fiber (NF) irradiated by an electron beam (energy: 0.5 MeV, dose: 0–20 kGy) were measured. The length and thickness of PP and NF are 80 ± 10 mm and 40–120 μm, respectively. The results show that the thermal conductivity and the tensile strength changed and became minimum, when the dose of the electron beam was 10 kGy. However, the effect of the dose on the deformation was not clear.     

Characterization of Dynamics in Materials Using Time-Resolved Electron Microscopy Incorporating Electron Counting and Electron Correlation Spectroscopy

Time-resolved electron microscopy incorporating electron counting and electron correlation spectroscopy can be used to quantify the dynamics in materials faster than the shot noise limit of the real-time observation in conventional transmission electron microscopy. An imaging electron beam current, temporally modulated by the dynamics of the specimen, is selected by the aperture in the image plane, and is measured by means of an electron counting technique. Applications of the method to the study of the dynamics of superconducting vortices and to the observation of nanovibrations of materials associated with elastic properties are discussed.     

基于共振光隧穿效应的角加速度传感器设计

阐述了一种基于共振光隧穿效应的角加速度传感器的设计方法,分析了其传感特性,并以共振光隧穿理论为基础,利用Mathematica软件进行了仿真分析。该加速度传感器的品质因数可以达到1.96×10⁸,远高于经典F-P腔的品质因数8.183×104。灵敏度可以达到0.1°/nm,     

线性化AlGaN/GaN HEMT费米能级与二维电子气密度关系的解析模型

通过化简复杂非线性的费米能级EF与二维电子气密度ns关系,并利用化简后函数的一阶泰勒多项式建立了线性化AlGaN/GaN HEMT中EF与ns关系的解析模型。该模型可以根据二维电子气密度ns的范围及温度计算EF与ns非线性关系之线性近似的参数斜率a和截距EF0。计算结果表明,所述模型的线性EF-ns计算结果对非线性精确解近似效果较好,且基于该模型计算的ns-VG曲线与实验数据符合良好。