Anomalies of the fractional quantum hall effect in a wide ballistic wire

Magnetotransport in a ballistic wire under the conditions of integer and fractional quantization was studied experimentally. A nonlinear magnetic-field dependence of filling factor (ν) of the Landau level was observed; this dependence arises if the self-consistent electrostatic potential of the wire has a specific form. It is assumed that the observed effect results from the influence of interaction between electrons at the partially occupied Landau level on this potential, which brings about a decrease in the electron concentration in the wire as the magnetic field increases in the case of ν<1.     

Thin wire hall effect devices

A thin wire inside a bulk semiconductor can concentrate the current density and the magnetic field strength to intensities that are significant for the Hall effect. Also, the self-magnetic field of the Hall currents can add to this intensification, particularly when there is axial symmetry and a toroidal configuration. The impedanceZiacross the ends of the wire is modified if a currentIflows between the semiconductor and the wire:|Zi| simeq omega / sigma . K_{H}. I[(b/a)^{k} -1]wherek = micro .sigma . K_{H}.I/(2.pi)andaandbare the inner and outer radii of a cylinder. A more complete analysis of the cylindrical field problem reveals that well-known results for skin effect are also modified by the current. The new solution is expressed by high-order Thompson functions, which include the ber and bei functions of skin effect as a special case. For values ofkgreater than 2, the solution can have a negative real wave impedance. Experiments are described for estimating changes in the Hall currents by counting flux jumps in a superconducting wire which is embedded in bulk bismuth. The Hall currents are magnified by the factor 5. In the course of the experiments, a pulse position modulator is realized. Other possible devices are realizable, notably an amplifier and a simple, rugged flip-flop.     

On the effect of electron-phonon interaction on the temperature dependences of magnetotransport in quantum hall systems

The effect of electron-phonon interaction on the temperature dependences of conductivity is studied in the mode of the integer quantum Hall effect. It is shown that electron-phonon interaction leads to the possibility of transport in the region of localized states, thus forming the shape of magnetotransport curves at a given temperature. The relation between scaling indices in the power laws describing the dependences of the widths of transition regions between successive plateaus of the quantum Hall effect on the temperature and localization length is determined within an analytical model as a function of the energy measured from a certain Landau-level center. Direct numerical calculations of the magnetotransport curves are performed at various temperatures. The results are in good agreement with theory and experimental data on the integer quantum Hall effect.     

Temperature- and potential-distributions determination method for hall plates,considering the effect of temperature-dependent conductivity and hall coefficient

An existing technique for determining the temperature distribution and the potential distribution of a Hall plate is extended to take into account the effect of the temperature-dependent conductivity and Hall coefficient. Equations to be used for that are presented. A practical example—the modeling of an intrinsic indium antimonide semiconductor-made Hall plate—is used to illustrate and evaluate the method using these equations.     

The hall effect in Fe submonolayer systems on n-and p-type Si(111)

The in situ Hall effect measurements at room temperature showed that formation of the atomically clean Si(111) 7×7 surface as a result of high-temperature annealing (T=1250°C, t=120–180 s) of n-Si reverses the majority carrier sign at the surface, and a hole-enriched layer is formed at the p-Si surface. The different dynamics of Hall and resistivity voltage variations within the first monolayer of iron adsorbed onto substrates with a p-n junction or with a hole-enriched layer is not related to conduction over the adsorbed layer. Conduction in the Fe layer of thickness exceeding three monolayers is caused in both cases by the transport of electrons with densities 2×10¹³–2×10¹⁴ cm^?2 and mobilities 65–90 cm²/(V s).     

Low-field anomaly of the hall effect in disordered two-dimensional systems

This study is devoted to investigation of the nonlinear behavior of the Hall resistance in low magnetic fields. When investigating two-dimensional electron gas in single GaAs/In _x Ga_{1 − x} As/GaAs quantum wells, it is shown that the anomaly of the Hall effect in disordered systems can be described taking into account the second-order quantum corrections to conductivity.     

Spin hall effect in semiconductor structures with spatially inhomogeneous spin relaxation

The extrinsic spin Hall effect in samples with coordinate-dependent relaxation time of the spin was studied. It was shown that the spin Hall effect in this case results in not only spatial separation of electrons with different spin projections, but also in the generation of a certain spin; therefore, the total spin’s moment of a sample became nonzero under an electric current. A two-layer structure with different times of spin relaxation in layers and a homogeneous sample with linear behavior of the surface’s spin relaxation were considered. An expression for the effective spin’s relaxation time, which defines the spin polarization distribution in thin films, was derived. It was shown that the uniform spins polarization parallel to the film plane is possible, if the film thickness amounts to several diffusion lengths of the spin.     

多功能会堂扩声系统的设计

阐述了通过计算机仿真辅助设计、数字网络技术等现代科技手段,实现多功能会堂扩声系统的优化设计.采用EASE软件对厅堂的建声及扬声器的布局进行了系统设计.通过在系统中采用Dante数字音频网络,实现了10个会议室以及多功能会堂之间的互联互通以及多功能会堂内应用场景的自由切换,提升了中央控制系统的综合应用功能,实现了复杂系统的简易的控制.系统测量结果达到了设计的要求.     

Single-peak excitonic emission of CdSe ultra-thin quantum wells finished with fractional monolayers

Ultra-thin quantum wells (UTQWs) of CdSe grown by atomic layer epitaxy (ALE) present very interesting features, such as intense excitonic luminescence and relatively narrow width. Grown under adequate conditions only a single excitonic peak is exhibited in the photoluminescence (PL) spectrum, indicating the absence of thickness fluctuations. The PL peak of an UTQW grown with the same nominal thickness presents a blue shift if grown at a higher substrate temperature. This energy shift is attributed to changes in composition: instead of a pure CdSe UQTW we obtain a Zn_1?xCd_xSe UTQW with Cd content depending on growth temperature. The fact that even changing the growth temperature only a single excitonic peak is observed is interpreted in terms of a homogeneous mixing of the Cd and Zn atoms at the upper interface. The lack of homogeneity would produce islands and terraces, and then thickness fluctuations that would be clearly evident in the PL spectrum. In order to verify this assertion we have grown UTQWs finished with fractional monolayers, around 0.5 ML of CdSe. We produced UTQWs with 2.5, 3 and 3.5 ML and the result is that all the samples presented a single peak, red shifted with increasing CdSe coverage and monotonic increase in the full-width at half-maximum (FWHM) of the emission. This confirms the homogenization of the CdSe–ZnSe interface.     

量子阱中弱耦合束缚极化子的温度效应

采用线性组合算符与变分相结合的方法研究了温度对无限深量子阱中弱耦合束缚极化子性质的影响.推导出在弱耦合情况下,无限深量子阱中束缚极化子的基态能量和振动频率与温度的关系.选择GaAs晶体为例,进行数值计算.结果表明:温度升高时,量子阱中弱耦合束缚极化子的振动频率增大；温度升高、阱宽增大时,量子阱中弱耦合束缚极化子的基态能...     

Theoretical analysis of hall factor and hall mobility in p-type silicon

Using a two-band (i.e. heavy-hole and light-hole band) model and the relaxation time approximation, the Hall factor was calculated for the case of silicon doped with boron. Contributions from scattering by acoustical and optical phonons and by ionized and neutral impurities were considered. In addition, the effects of hole-hole scattering, as well as valence band nonparabolicity and anistropy were also taken into account. The scattering and anistropy factors were separately evaluated to emphasize their individual contributions to the Hall factor. Theoretical values of the Hall factor at 300 K vary between 0.882 and 0.714 over the dopant density ranges 10¹⁴ ≦ N_A ≦ 3 × 10¹⁸ cm^?3. Hall mobilities for p-type silicon were calculated and compared with published data 100 ≤ T ≤ 400 K and 10¹⁴ ≦ N_A ≦ 3 × 10¹⁸ cm^?3. The present model is limited to the case of uncompensated material and for the weak field in which μ_HB ? 1.     

The accuracy of the relaxation solution for the potential problem of a hall plate with finite hall electrodes

The potential values of the relaxation method are converted to the values of the geometrical coefficient and the Hall side resistance. As a guide to the accuracy of the data obtained from the relaxation method, these converted values are compared with the known conformal transformation solutions. A conclusion is found upon the variation of the geometrical coefficient and the Hall side resistance with the mesh size and the Hall electrode length. The paper concludes by demonstrating new data which may be difficult to obtain by the analytical method.     

量子阱中弱耦合束缚极化子的温度效应

采用线性组合算符与变分相结合的方法研究了温度对无限深量子阱中弱耦合束缚极化子性质的影响。推导出在弱耦合情况下,无限深量子阱中束缚极化子的基态能量和振动频率与温度的关系。选择GaAs晶体为例,进行数值计算。结果表明：温度升高时,量子阱中弱耦合束缚极化子的振动频率增大;温度升高、阱宽增大时,量子阱中弱耦合束缚极化子的基态能量的绝对值增大。     

基于分数泰伯效应的双波长微距分束的研究

微距光谱分束是红外领域小型双波段成像系统的关键技术之一。利用菲涅耳衍射理论和角谱理论,研究了双波长和宽角度入射光场通过阶梯光栅在分数泰伯距离下的衍射特性。建立了基于阶梯光栅的双探测阵列成像模型,数值模拟了入射波长分别为4 m和4.5 m的光束在-30~30入射角度范围的光栅分束结果,获取了探测面上的发光强度、能量和信噪比等参数值。此文的研究成果可为构建微型双波段成像装置及设计精密光谱分束器件提供理论支持。     

The fractional discrete cosine transform

The extension of the Fourier transform operator to a fractional power has received much attention in signal theory and is finding attractive applications. The paper introduces and develops the fractional discrete cosine transform (DCT) on the same lines, discussing multiplicity and computational aspects. Similarities and differences with respect to the fractional Fourier transform are pointed out     

The discrete fractional Fourier transform

We propose and consolidate a definition of the discrete fractional Fourier transform that generalizes the discrete Fourier transform (DFT) in the same sense that the continuous fractional Fourier transform generalizes the continuous ordinary Fourier transform. This definition is based on a particular set of eigenvectors of the DFT matrix, which constitutes the discrete counterpart of the set of Hermite-Gaussian functions. The definition is exactly unitary, index additive, and reduces to the DFT for unit order. The fact that this definition satisfies all the desirable properties expected of the discrete fractional Fourier transform supports our confidence that it will be accepted as the definitive definition of this transform     

Phase tree: a periodic, fractional flux quantum vernier forhigh-speed interpolation of analog-to-digital converters

A Josephson junction circuit that can rapidly track and record a magnetic flux signal to a small binary fraction of the flux quantum is proposed. This so-called phase tree circuit behaves periodically, recording the residue of the signal modulo the flux quantum in 2^p ths of a flux quantum for a p-level binary tree. Signal quantization is accomplished by comparators that read the 2^p-1 circulating currents in the leaf-level branches, providing a total of 2^p possibilities in the periodic code. The phase tree can therefore be used as a vernier, linear over a large number of periods because a single analog element determines the quantization levels once the network is properly biased. A system consisting of a conventional m-bit analog-to-digital converter (ADC m≈4-7) and an auxiliary p-bit phase tree interpolator (p≈2-5) can achieve at least m+p -1 bits without loss of bandwidth or sample rate     

新加坡滨海艺术中心音乐厅的声学特性

新加坡滨海艺术中心音乐厅是目前全世界声学规模最大、声学设置最复杂和齐全的音乐厅，并采用混响室来控制音乐厅自然混响。对该音乐厅的设计思想、结构特征、声学控制机构以及音乐厅建成后实测的声学特性作了比较全面的介绍。