On the thermoelectric power in quantum well of A 3 II B 2 V semiconductors in the presence of a classically large magnetic field

Summary An attempt is made to study the thermoelectric power of the carriers in quantum well of A ₃ ^II B ₂ ^V semiconductors, taking Cd₃As₂ quantum well as an example. It is found, on the basis of newly derived 2DE−k _s dispersion relation by including various types of anisotropies in the energy spectrum that the thermoelectric power decreases with increasing electron concentration and decreasing film thickness respectively. In addition, the corresponding well-known results for bulk specimens of isotropic parabolic energy bands are also obtained from the expressions derived.     

Crystal-field and superposition model analysis of :BaY F ( = Er, Dy, Nd)

The experimental values of the energy levels of Er³⁺, Dy³⁺, and Nd³⁺ in BaY₂F₈ were fitted to a single-ion Hamiltonian containing free-ion and crystal-field interactions. The crystal-field parameters so evaluated were then analyzed by using Newman's Superposition Model. The agreement between the two sets of parameters is good, provided a possible distortion of the F^- polyhedron around the rare-earth site is taken into account. The effects of a possible displacement of the rare-earth ion substituting for Y³⁺ are also evaluated. Received 14 May 2002 / Received in final form 12 July 2002 Published online 17 September 2002     

Effect of pressure on turnover behaviour inI–V characteristic curves in GeTeSe chalcogenide glass

Summary Thick layers of GeTeSe chalcogenide glass have been prepared and subjected to conduction measurements under the effect of both temperature and pressure. The results of theI–V characteristics exhibit transition from high-resistance state to differential negative resistance state through a turnover point. The application of uniaxial pressure shows the similar effect of temperature on that behaviour. Both current and voltage at the turnover point depend on pressure and ambient temperature. The rise of temperature in the conduction path due to joule heating and application of uniaxial pressure as well as the reduction in the energy gap width (β=2.87·10⁻¹²eV/N m⁻²) are estimated and discussed at the turnover point. This behaviour is explained according to the orientation of dipoles randomly dispersed in viscous amorphous matrix.     

Transport properties of a nanotube-based transistor

Transport properties of doped nanotube-based double junctions forming a nanotransistor are investigated within the tight binding formalism. The effects of doping, gate length and gate-source hopping have been considered. It is found that in addition to the importance of rotational symmetry in determining transport properties, large gains can be achieved for semiconducting doped tubes. Received 30 November 2000     

Effects of Pressure on Doped Kondo Insulators

The effects of pressure on the doped Kondo insulators (KI) are studied in theframework of the slave-boson mean-field theory under the coherent potential approximation.A unified picture for both the electron-type KI and hole-type KI is presented. The density ofstates of the f -electrons under the applied pressures and its variation with the concentrationof the Kondo holes are calculated selficonsistently. The specific heat coefficient, the zerotemperaturemagnetic susceptibility as well as the low-temperature electric resistivity of thedoped KI under various pressures are obtained. The two contrasting pressure-dependent effectsobserved in the doped KI systems can be.naturdy explained within a microscopic model.     

On the Optical Conductivity of Kondo Insulators

The temperature-dependent optical conductivity of a Kondo insulator for different temperatures with impurity doping on the conduction band is studied within the U = ∞ Anderson lattice model in the framework of a slave-boson mean-field theory under the coherent potential approximation. The results show that the depletion of the optical conductivity in low-frequency region decreases with increasing of the temperature, and the system exhibits a transition between a low-temperature insulating phase and a high-temperature metallic phase. With increasing of the impurity concentration, the effect of the impurity scattering could result in a nearly temperature-independent gap behavior. The numerical results on the localization of the electron and its variation with temperature are also discussed with the help of optical sum rule.     

时间反演对称性破缺系统中的拓扑零能模

Su-Schreiffer-Heeger模型预测了在一维周期晶格的边缘处可能出现零维的拓扑零能模,其能量本征值总是出现在能隙的正中间.本文以半导体微腔阵列中光子和激子在强耦合情况下形成的准粒子为例,通过准粒子的自旋轨道耦合与Zeeman效应,研究了时间反演对称性破缺对拓扑零能模的影响.发现拓扑零能模的能量本征值可以随着自旋轨道耦合强度的变化在整个带隙内移动,自旋相反的模式移动方向相反;在二维微腔阵列中发现了沿着晶格边缘移动的拓扑零能模,提出了一维零能模的概念.由于时间反演对称性的破缺,这种一维拓扑零能模解除了在相反传输方向上的能级的简并,从而在传输过程中出现极强的绕过障碍物的能力.     

非均匀积污下高压绝缘子电位及电场分布特性

高压绝缘子在输变电工程中承担着绝缘的重要角色. 由于工业化的飞速发展, 雾霾和沙尘等天气的频繁出现, 污秽颗粒在大气流场的作用下在绝缘子表面沉积, 容易发生污闪事故, 严重影响着电网的安全运行. 将高压绝缘子污闪发生的主要过程-绝缘子的动态积污和表面电场畸变过程进行耦合分析, 探究污闪发生的机理. 建立绝缘子周围的欧拉-欧拉气固两相流模型, 对绝缘子动态积污过程进行数值模拟, 获得绝缘子表面的非均匀积污层分布; 创建其表面导电层单元, 结合有限元方法建立积污绝缘子电场模型, 对非均匀积污层分布的绝缘子串进行电位及电场分析. 研究结果表明: 在积污层非均匀分布情况下, 绝缘子表面积污层周向位置对其电位分布的趋势影响较小, 但对绝缘子表面电场畸变的发生位置影响较大. 随着周向位置的变化, 电场畸变位置的偏移也不同, 且侧风面电场畸变的偏移最大. 随着积污层电导率的增大, 电场强度大于清洁绝缘子表面的场强, 且背风侧的场强畸变最大.      

合成绝缘子的性能与缺陷检测

主要探讨了合成绝缘子的各种性能 ,指出运行中出现的问题 ,介绍了几种缺陷检测方法 ,并对今后的发展做了预测