Transition between synchronization and chaos in doped GaAs/AlAs superlattices

The transition between chaotic and periodic regimes in spontaneous current oscillations of weakly coupled, doped GaAs/AlAs superlattices has been observed by varying the external d.c. bias. The chaotic current oscillations are observed for voltage ranges, which exhibit a large negative differential conductance in the time-averaged I–V characteristic. Since this system can be described by a spatially distributed, non-linear system with many degrees of freedom, the coupling between the degrees of freedom in the chaotic windows is repulsive, while in the periodic windows it is attractive.     

Semiclassical theory of persistent current fluctuations in ballistic chaotic rings

The persistent current in a mesoscopic ring has a Gaussian distribution with small non-Gaussian corrections. Here we report a semiclassical calculation of the leading non-Gaussian correction, which is described by the three-point correlation function. The semiclassical approach is applicable to systems in which the electron dynamics is ballistic and chaotic, and includes the dependence on the Ehrenfest time. At small but finite Ehrenfest times, the non-Gaussian fluctuations are enhanced with respect to the limit of zero Ehrenfest time.     

Reprint of : Semiclassical theory of persistent current fluctuations in ballistic chaotic rings

The persistent current in a mesoscopic ring has a Gaussian distribution with small non-Gaussian corrections. Here we report a semiclassical calculation of the leading non-Gaussian correction, which is described by the three-point correlation function. The semiclassical approach is applicable to systems in which the electron dynamics is ballistic and chaotic, and includes the dependence on the Ehrenfest time. At small but finite Ehrenfest times, the non-Gaussian fluctuations are enhanced with respect to the limit of zero Ehrenfest time.     

Strong impact of impurity bands on domain formation in superlattices

The formation of electric field domains in doped semiconductor superlattices is described within a microscopic model. Due to the presence of impurity bands in low-doped samples the current–voltage characteristic is essentially different compared to medium-doped samples.     

Tunable Fano resonances in the ballistic transmission and tunneling lifetime in a biased bilayer graphene nanostructure

Dynamics of the Dirac fermions, in particular the transmission coefficient and the resonant tunneling lifetime are studied across a bilayer graphene electrostatic double barrier structure modulated by an in plane homogeneous electric field. Asymmetric Fano type resonances are noted for the first time in the transmission spectrum of the bilayer graphene nanostructures and are found to be highly sensitive to the direction of incidence of the charge carriers and the applied homogeneous electric field. The effect of the external field on the extended and the evanescent modes is also analysed. Resonant tunneling lifetime is found to be highly anisotropic in nature. The chiral carriers are either accelerated or decelerated by the electric field depending on the energy of the quasi-bound states, the angle of incidence and the magnitude of the applied field. Effects of the external field on the localization of the chiral carriers are also discussed.     

Resonant tunneling in weakly coupled GaAs/AlGaAs superlattices in a transverse magnetic field: A probe of electronic distribution function

A method is proposed to get information about carrier distribution function in superlattices and multiple quantum-well structures from the analysis of the vertical transport experiments in a transverse magnetic field. The method was applied to the GaAs/AlGaAs superlattices with wide quantum wells in strong (B=0–7 T) magnetic fields. It was shown that the distribution function of electron is nonequilibrium Boltzmann-like, with electronic temperature T=10–20 K.     

电场对量子阱中激子能级宽度的影响

本文把固体中较大窨范围运动的粒子作为准经典粒子来描述。将已导出的能量测不准公式和激子的经典力学模型应用到电场下GaAs/GaAlAs量子阱中,激子能级宽度的计算结果与测量结果基本吻合,能较清楚、简单地解释纵向电场和横向电场下激子光吸收线宽的很大的差异。     

电场对量子阱中自由载流子光辐射线宽的影响

本文对固体中在较大空间范围运动的粒子采用轨道、动量及波包来描述。根据量子力学测不准关系, 粒子的能量测不准公式被导出。公式表明, 电场强烈地散射载流子, 使载流子所处能级大为展宽。应用该公式到Ｐ－Ｉ－Ｎ结构的ＧａＡｓ／ＧａＡｌＡｓ 多量子阱中, 理论计算的光辐射线宽与光致荧光实验测得的线宽吻合。     

Ultimate performance of quantum well infrared photodetectors in the tunneling regime

Thanks to their wavelength diversity and to their excellent uniformity, Quantum well infrared photodetectors (QWIP) emerge as potential candidates for astronomical or defense applications in the very long wavelength infrared (VLWIR) spectral domain. However, these applications deal with very low backgrounds and are very stringent on dark current requirements. In this paper, we present the full electro-optical characterization of a 15 μm QWIP, with emphasis on the dark current measurements. Data exhibit striking features, such as a plateau regime in the I(V) curves at low temperature (4–25 K). We show that present theories fail to describe this phenomenon and establish the need for a fully microscopic approach.     

The polaron effect on the binding energy of a shallow donor impurity in quantum-well wires in an electric field

Using a variational technique, the effect of electron-longitudinal optical (LO) phonon interaction on the ground and the first few excited states of a hydrogenic impurity in a semiconductor quantum wire of rectangular cross section under an external electric field is studied theoretically for the impurity atom doped at various positions. The results for the binding energy as well as polaronic correction are obtained as a function of the size of the wire, the applied uniform electric field and the position of the impurity. It is found that the presence of optical phonons changes significantly the values of the impurity binding energies of the system. Taking into account the electron–LO phonon interaction the 1s→2p_y and 1s→2p_z transition energies are calculated as a function of applied electric field for different impurity positions.     

Tilted electric field effects on the electronic states in a GaAs quantum disk

In the present work we report the effects of a geometrical confinement and tilted applied electric field on the electronic energy levels in a semiconducting quantum disk. Calculations are performed in the effective mass approximation and using a variational method. The results can be summarized as follows: (1) due to the infinite confinement along the all directions of the heterostructure, the variational calculation with two parameters for tilted applied electric field can be treated with two independent each other variational parameters; (2) the magnitude of the energy shift is an increasing function of the applied electric field; (3) the effects of the applied electric field are magnified as the dimensions of the heterostructure (height and radius) grow; and finally (4) for large enough applied electric field the energy shift is a linear function of the applied electric field.     

Electron–phonon effect on the ground-state binding energy of hydrogenic impurity in quantum-well wire in presence of an electric field

The hydrogenic impurity binding energy in rectangular quantum well wire including both barriers of finite height and an applied electric field are studied. The polaron effects on the ground-state binding energy in electric field are investigated by means of Landau-Pekar variation technique. The results for the binding energy as well as polaronic correction are obtained as a function of the size of the wire, the applied electric field and the position of the impurity. Our calculations are compared with previous results in quantum wires of comparable dimensions.     

Polaron effects on the binding energy of a hydrogenic impurity in parabolic quantum wires in perpendicular electric and magnetic fields

Using a variational approach, the binding energy of shallow hydrogenic impurities in a parabolic quantum wire is calculated within the effective mass approximation. The polaron effects on the ground-state binding energy in electric and magnetic fields are investigated by means of the Pekar–Landau variation technique. The results for the binding energy as well as a polaronic correction are obtained as a function of the applied fields and the impurity positions.     

Quantum chaos and magnetotransport in lateral superlattices: The transition from weak to strong modulation potential

Magnetotransport in lateral superlattices covers a variety of apparently different physics dependent on the amplitude of the modulation potential relative to the Fermi energy ranging from the weakly modulated 2DEG to the antidot lattice. Here we investigate the transition between weak modulation and antidots within the quantum-mechanical theory by studying (i) the single-particle spectrum with respect to quantum signatures of classical chaos and (ii) the change of characteristic features in the magnetoresistance starting from the Kubo formula.     

Effect of external noise on the current response in superlattices

Within the single-band model and the nearest-neighbor approximation we investigate the effect of external noise on the current response driven by dc–ac field which has a fluctuating component. We find the external noise can destroy the current resonant peaks. When the strength of the external noise becomes enough large, all the current resonant peaks will completely disappear.     

Effect of nonequilibrium phonons on the tunnel current in superlattices

We present the first measurements of the effect of nonequilibrium phonons on the tunnel current in a weakly coupled GaAs/AlAs superlattice. The phonon-induced current has a maximum at a bias voltage which varies linearly with phonon source temperature at both zero and applied magnetic fields (B = 6 T). We attribute these results to assisted tunnelling by stimulated phonon emission and show that this system can be used as a phonon spectrometer.     

外加条件及两种电子传输对量子点红外探测器噪声的影响

基于外加电场对电子漂移速度的影响,考虑激发能对微米尺度和纳米尺度电子传输的依赖,通过计算仿真研究了外加条件及两种电子传输对量子点红外探测器噪声的影响.结果表明:在2545kV/cm外加电场下,噪声模型和实验数据吻合;噪声随着外加电场和温度的增加而增加,当温度小于80K时噪声增加迅速,而当温度大于80K时噪声增加缓慢,并且温度越低噪声随外加电场变化越明显;噪声不随微米尺度电子传输激发能的变化而变化,随着纳米尺度电子传输激发能的增加而减小,随着纳米尺度电子传输激发能变化速度的增加而增加.该研究可为量子点红外探测器的优化设计和性能提高提供理论参考.     

Effect of electric fields on the ion current signals in a constant volume combustion chamber

Ion current sensing has the potential to become a promising combustion diagnostic technique for mass productive engines. In this paper, the effect of electric fields on ion current signals measured from a series of methane/air flames in a constant volume combustion chamber (CVCC) is investigated both experimentally and numerically. Based on simultaneous flame Schlieren imaging and ion current measurement, the relation between the flame/electrodes contact area and the ion current signal waveform is explored under different electric field configurations. A CFD model, which incorporates flame plasma hydrodynamics, neutral/charged species reaction kinetics and ion-electric field interactions, is constructed. The effect of the electric field on the ion distribution and the charged species flux are analyzed, and the signal amplitude and timing are well predicted under the equivalence ratio range of Ф?=?0.7–1.1. Besides, the behavior of electrons, which is normally neglected in previous studies, is also analyzed in this work. The results show that it will affect the signal as well. The electron produced in the flame front zone can hardly diffuse into the pre-flame zone (<?350?K) even its mobility is 3-4 order higher than those of the positive ions. Therefore, the anode of the ion probe, which placed in the pre-flame zone, cannot detect the ion current signal until it contacts the flame front.     

Numerical study on formation of electronic quantum states due to self-coherency in a non-periodic system

In order to investigate formation process of electronic quantum states in a confined system, we simulate motion of a wavepacket state and show how an eigenstate is formed due to coherence of electronic wave from the viewpoint that an eigenstate arises as a result of self-interference of a moving electron. Numerical results for a Hénon–Heiles potential in which chaotic motion can occur in the classical mechanics indicate that electronic eigenstates can arise even when motion of an electron is non-periodic. The results show that, in the quantum mechanics, periodicity is unnecessary for the formation of eigenstates.     

Effect of structural defect on phonon transmission quantization in low-dimensional superlattices

Using the scattering-matrix cascading method, we investigate the effect of structural defect on the acoustic phonon transmission quantization in a low-dimensional superlattice quantum waveguide. In the present system, the phonon transmission exhibits rather complex resonant behaviors. It is found that a lateral defect in an otherwise periodic structure modifies the transversal phonon transmission spectra nontrivially and completely washes away the transmission quantization due to the strong additional scattering by defect. However, the appreciable quantization survives in the presence of a longitudinal defect. Our results also show that by adjusting the geometric parameters of the structural defect, one can control the phonon transport of the structure to match practical requirements in devices.