Widths of the Hall Conductance Plateaus

We study the charge transport of the noninteracting electron gas in a two-dimensional quantum Hall system with Anderson-type impurities at zero temperature. We prove that there exist localized states of the bulk order in the disordered-broadened Landau bands whose energies are smaller than a certain value determined by the strength of the uniform magnetic field. We also prove that, when the Fermi level lies in the localization regime, the Hall conductance is quantized to the desired integer and shows the plateau of the bulk order for varying the filling factor of the electrons rather than the Fermi level.     

聚酯的高温电晕充电和电荷在体内的输运

本文讨论常温和高温下恒压电晕充电聚酯(Mylar PETP)的电荷贮存稳定性问题。比较了聚酯的较低温位(85℃)TSD(thermally stimulated discharge)偶极峰与非极性分子聚合物材料较低温位TSD空间电荷峰对电荷稳定性影响的明显区别。通过不同高温电晕充电和常温充电后TSD过程中电荷重心的迁移,及相应温度下体电导率增长曲线的测量,研究了电导率对注入电荷平均深度的影响和脱阱电荷在该材料内的输运规律。 关键词：     

The role played by a polymer matrix in the transfer of charge carriers in molecularly doped polumers

Transient current curves were recorded for polystyrene and polycarbonate doped with 15 wt % tritolylamine using both surface and volume charge carrier generation. The multiple trapping model was used to perform numerical calculations of time-of-flight curves for the published Gaussian disorder model parameters. The calculation results were compared with the experimental data. It was shown that the experimental and calculated curves satisfactorily coincided. The flat plateau observed in time-of-flight curves should not be associated with the establishment of a quasi-equilibrium transport regime.     

Time-dependent transport properties in quantum well with thin inserted layer

We investigate the time-dependent transport properties of quantum well on the situation of nonlinear bias, where a thin potential well layer is inserted in the main quantum well. In our calculations, we consider the effects from all kinds of phonon interactions in the device. We find that the charge redistribution and electron motion in the whole structure play an important effect on the final current-voltage (I-V) curve. We also find an evident current hysteresis region and current high-frequency oscillation with time in this particular region. The results show that the inserted potential well layer can make the current hysteresis width narrower than that in the single quantum well structure, and it also damps the current oscillation. Due to the existence of the inserted layer, the plateau structure of I-V curve found in the single quantum well disappears.     

On the possibility of wake-field effects in the conductivity of doped semiconductors

The formation of a wake field around a swift ion passing through an electron gas and the resulting contribution to the stopping power acting on the ion is an intensively studied phenomenon in metals and semiconductors. The present investigation serves to clarify whether an analogous effect, namely the formation of wake fields and a corresponding contribution to the resistivity, might occur in the Galilei-transformed case of electronic transport in doped semiconductors where the gas of drifting charge carriers passes through an array of fixed impurity ions. By use of an appropriate dynamical screening theory we show that indeed a local plateau in the current density versus field characteristic has to be expected whenever the mean drift energy per carrier exceeds the sum of the mean thermal carrier energy and the zero-point energy of the longitudinal plasma mode of the carrier gas. However, our survey of the published literature suggests that this condition might be too stringent, at least for bulk materials and standard experimental situations, where the strong carrier heating in the high-field regime of relevance in combination with other drift-limiting mechanisms or interband electron-hole avalanching would always precede and prevent the formation of the wake.Dedicated to Prof. H.-J. Queisser on the occasion of his 60th birthday     

Transverse dispersion and interfacial dephasing effects on the shape and amplitude of the ballistic-electron-emission spectroscopy of nanographenes

We investigate charge transport across metal-molecule-metal junctions, i.e. hexagonal and triangular nanographene molecular layers sandwiched between Pt and Pd thin films, as measured by ballistic-electron-emission spectroscopy (BEEM). The measured shape of current-voltage curves cannot be explained in the framework of existing BEEM theories of bulk inorganic semiconductors. We develop a tight-binding model for the BEEM process and propose that the energetic dispersion of molecular layers and the dephasing effect due to the interface states account for the anomalous BEEM current-voltage behavior and play an important role in determining the shape of the curve. The electron-phonon scattering can also affect the shape of current-voltage curves.     

Quantifying the chiral magnetic effect from anomalous-viscous fluid dynamics

The Chiral Magnetic Effect(CME) is a macroscopic manifestation of fundamental chiral anomaly in a many-body system of chiral fermions, and emerges as an anomalous transport current in the fluid dynamics framework. Experimental observation of the CME is of great interest and has been reported in Dirac and Weyl semimetals. Significant efforts have also been made to look for the CME in heavy ion collisions. Critically needed for such a search is the theoretical prediction for the CME signal. In this paper we report a first quantitative modeling framework, Anomalous Viscous Fluid Dynamics(AVFD), which computes the evolution of fermion currents on top of realistic bulk evolution in heavy ion collisions and simultaneously accounts for both anomalous and normal viscous transport effects. AVFD allows a quantitative understanding of the generation and evolution of CME-induced charge separation during the hydrodynamic stage, as well as its dependence on theoretical ingredients. With reasonable estimates of key parameters, the AVFD simulations provide the first phenomenologically successful explanation of the measured signal in 200 AGe V Au Au collisions.     

表层氟化聚乙烯中的空间电荷

本文试图简要地汇集近年来与近期我们所取得的关于表面氟化对聚乙烯(PE) 空间电荷行为影响的研究结果, 总结与探讨PE中的空间电荷积累与其氟化层特性和特征间的关联. 这些结果显示在氟化反应气中没有氧存在时一个非常薄的氟化层能产生有效的电荷抑制, 而当氧存在时为达到有效的电荷阻挡、需要一个具有高氟化度的非常厚的氟化层. 在影响空间电荷的诸电学因素中, 氟化层的电荷传导特性比其电荷俘获特性和介电常数或极性对阻止电荷注入材料内部更为重要, 尽管氟化层的高介电常数和被俘获的电荷会降低界面电场、因此减少电荷的电极注入. 氟化层的电荷传导特性密切关联于其自由体积, 反应混合气中存在的氧对减小自由体积、因此对电荷的抑制具有强的负面影响.     

自旋轨道耦合作用下石墨烯pn结的电子输运性质

本文研究了自旋轨道耦合作用下石墨烯纳米带pn结的电子输运性质. 当粒子的入射能量处于pn结两端势能之间时, 粒子将会以隧穿的形式通过石墨烯pn结, 同时伴随着电子空穴转换. 电导随费米能的变化曲线呈不等高阶梯状, 并在费米能位于pn结两端能量中点时取得最大值. 随着石墨烯pn结长度的增加, 电导以指数形式衰减. 自旋轨道耦合作用导致的能隙会使电导显著减小, 而边缘态的粒子则可以几乎毫无阻碍地通过pn结. 本文用一个简单的子带隧穿模型解释了上述特征. 最后还研究了在pn转换区中掺入替位杂质的情况. 在弱杂质下, 电导随费米能变化的曲线将不再对称; 当杂质较强时, 仅边界态的形成的电导台阶能够保持.     

Effect of epitaxial crystallization on packet-like space charge characteristics in low-density polyethylene under multi-field coupling conditions

In order to study the effect of epitaxial crystallization on charge transport in low-density polyethylene (LDPE) under multi-field coupling conditions, three typical epitaxial crystallizations, namely disorder (glass substrate), crossover (isotactic polypropylene substrate), and parallel (polytetrafluoroethylene substrate), were prepared and denoted as LD-G, LD-iPP, and LD-PT, respectively. Packet-like space charge through samples was analyzed by the pulsed electro-acoustic (PEA) method. It is shown that different microscopic surface morphologies appeared in the LDPE samples with different epitaxial crystallizations, which, however, do not change the crystalline structure of the bulk. Packet-like space charge phenomena were observed and the distortion field increased with the temperature which could be attributed to the larger amount of charge injection in a shorter period. The differences of the amount and injection rate of the space charge were explained and verified considering the typical chain alignment of epitaxial crystallization, which, in our opinions, contributes to the pass over of positive charge in LD-iPP samples.     

Semiconductor nanocrystals in carrier-transporting polymers: Charge generation and charge transport

By incorporating semiconductor nanocrystals in carrier-transporting polymers, an interesting class of photoconductive nanocomposites is created. The presence of semiconductor nanocrystals enhances the photoinduced charge generation efficiency and extends the sensitivity range, while the polymer matrix is responsible for charge transport. A wide variety of semiconductors and polymers have been used. In this paper, we review material synthesis and discuss the effects of semiconductor nanocrystals on the charge transport and charge generation properties.     

Dynamics of charged bulk viscous collapsing cylindrical source with heat flux

In this paper, we have explored the effects of dissipation on the dynamics of charged bulk viscous collapsing cylindrical source which allows the out-flow of heat flux in the form of radiations. The Misner–Sharp formalism has been implemented to drive the dynamical equation in terms of proper time and radial derivatives. We have investigated the effects of charge and bulk viscosity on the dynamics of collapsing cylinder. To determine the effects of radial heat flux, we have formulated the heat transport equations in the context of Müller–Israel–Stewart theory by assuming that thermodynamics viscous/heat coupling coefficients can be neglected within some approximations. In our discussion, we have introduced the viscosity by the standard (non-causal) thermodynamics approach. The dynamical equations have been coupled with the heat transport equation; the consequences of the resulting coupled heat equation have been analyzed in detail.     

Study of the transport mechanism in molecular self-assembling devices

This paper focuses on the intrinsic charge transport in self-assembled monolayers (SAMs) and on the nature of transport in organic systems, in which surface and bulk properties are undistinguishable due to scale of consistent materials. Developed SAM-OFETs and photovoltaic (SAM-PVC) devices are characterized independently to study a role of charge delocalization both in electrical and optical manifold. The dynamics of charge transport are determined and used to clarify a transport mechanism. Taken together, these SAM devices provide a unique tool to study the fundamentals of polaronic transport on organic surfaces and to discuss the SAM-OFET and SAM PVC performance. Vapor phase molecular self-assembly of 1, 4, 5, 8-naphthalene-tetracarboxylic diphenylimide (NTCDI) having a rich π-stacking charge delivery system is used to enhance the performance of SAM-OFET and SAM PVC devices. Charge mobility in SAM-OFET could achieve values of more than 30 cm² V⁻¹ s⁻¹. The dynamics of charge transport in NTCDI-derived SAM-OFETs were probed using time-resolved measurements in an NTCDI-derived photovoltaic cell device. Time-resolved photovoltaic studies allow us to separate the charge annihilation kinetics in the conductive NTCDI channel from the overall charge kinetic in a SAM-OFET device. It has been demonstrated that tuning of the type of conductivity in NTCDI SAM-OFET devices is possible by changing Si substrate doping. In addition, the possibility of measuring transport in highly ordered SAM structures shines light on the polaron charge transfer in organic materials. Our study proposes that a cation-radical exchange (redox) mechanism is the major transport mechanism in SAM nanodevices. The role and contribution of the transport through delocalized states of redox active surface molecular aggregates of NTCDI are exposed and investigated in this report.     

Comparison of influence of fluidization time on electrostatic charge build-up in the bubbling vs. slugging flow regimes in gas–solid fluidized beds

Electrostatic charge generation poses significant problems in some commercial gas–solid fluidized bed reactors such as those in gas-phase polyolefin production. Understanding the contributing factors to charge generation is important in determining the charge generation mechanisms, leading to the development of methods to reduce or prevent this phenomenon. This work focused on determining the effect of fluidization time on particle charging and the amount of particle adhesion on the fluidization column wall in both the bubbling and slugging flow regimes. The charging effect was investigated for particles in three regions of the fluidized bed: elutriated fines, bulk particles inside the bed, and particles adhered to the column wall. The particles size distribution, mass and charge were measured for all three regions. Fluidization was carried out with polyethylene resins from an industrial reactor; times of 15, 30, 60, 120, 180, and 360 min were evaluated. Increased fluidization time decreased the amount of particles mass collected in the bulk region and increased those adhered to the column wall during the velocities tested in the bubbling flow regime. Whereas the quantity of particles in each region was not affected by fluidization time for the velocities examined in the slugging flow regime. Bipolar charging was observed with relatively smaller particles becoming predominately positively charged and larger particles becoming predominately negatively charged. Each region of the bed affected the magnitude of net q/m, with elutriated fines having the largest magnitude, followed by those adhered to the column wall, and finally those in the bulk of the bed. Charge saturation was attained for fluidization times greater than 60 min for particles in the bulk and along the column wall for all gas velocities. However, extended fluidization times were required with the entrained fines in bubbling flow; whereas charge saturation of fines in slugging flow occurred shortly after the onset of fluidization. Mean particle diameter for each measurement region was not impacted by the fluidization time for any of the gas velocities tested. The bed hydrodynamics was found to definitely have an impact on the particle–wall fouling where the particle layer continued to develop on the inner column wall as fluidization time increased for those velocities in the bubbling regime while comparatively less impact on particle layer growth was observed in the slugging flow regime. In addition, the bubbling flow regime resulted in particle layers formed on the column wall to be longer and thinner whereas those formed in the slugging flow regime were shorter and thicker.     

Selective probing of photoinduced charge and spin dynamics in the bulk and surface of a topological insulator

Topological insulators possess completely different spin-orbit coupled bulk and surface electronic spectra that are each predicted to exhibit exotic responses to light. Here we report time-resolved fundamental and second harmonic optical pump-probe measurements on the topological insulator Bi(2)Se(3) to independently measure its photoinduced charge and spin dynamics with bulk and surface selectivity. Our results show that a transient net spin density can be optically induced in both the bulk and surface, which may drive spin transport in topological insulators. By utilizing a novel rotational anisotropy analysis we are able to separately resolve the spin depolarization, intraband cooling, and interband recombination processes following photoexcitation, which reveal that spin and charge degrees of freedom relax on very different time scales owing to strong spin-orbit coupling.     

考虑空间电荷层效应的氧离子导体电解质内载流子传输特性

晶界或异质界面诱发的空间电荷层(space charge layer,SCL)效应,被认为是氧离子导体电解质内界面附近区域载流子传输特性显著区别于体相区域的关键原因之一.现有研究多采用Poisson-Boltzmann(PB)方程预测SCL效应的影响规律,但其基于载流子电化学平衡假设,无法用于载流子存在宏观运动的工况,极大限制了相关传输机理研究.本文耦合Poisson方程和载流子质量守恒方程,建立了适用于载流子具有宏观运动时氧离子导体内载流子传输过程的模型,推导了控制SCL效应的关键无量纲参数.聚焦固体氧化物燃料电池中常用的AO2-M2O3氧离子导体电解质,对比研究了传统PB方程和本文建立的Poisson-载流子质量守恒耦合方程的预测结果可靠性.进一步采用耦合模型深入分析了考虑SCL效应时氧离子导体内部氧空位传输机理,发现导体界面电流密度增大导致SCL电阻先减小后增大.增大无量纲Debye长度(表征空间电荷层厚度与导体厚度的比值)可显著增大SCL电阻.当驱动氧空位移动的过电势与热势数量级相当时,增大无量纲电势(表征过电势与热势的比值)导致SCL电阻增大;当过电势远小于热势时,改变无量纲电势对氧空位传输过程几乎无影响.本文研究结论可为通过合理设计晶界或异质界面以改善氧离子导体内载流子传输能力及最终提高相关电化学器件性能提供理论依据.     

Gap opening in the zeroth Landau level in gapped graphene: pseudo-Zeeman splitting in an angular magnetic field

We present a theoretical study of gap opening in the zeroth Landau level in gapped graphene as a result of pseudo-Zeeman interaction. The applied magnetic field couples with the valley pseudospin degree of freedom of the charge carriers leading to the pseudo-Zeeman interaction. To investigate its role in transport at the charge neutrality point (CNP), we study the integer quantum Hall effect in gapped graphene in an angular magnetic field in the presence of pseudo-Zeeman interaction. Analytical expressions are derived for the Hall conductivity using the Kubo-Greenwood formula. We also determine the longitudinal conductivity for elastic impurity scattering in the first Born approximation. We show that pseudo-Zeeman splitting leads to a minimum in the collisional conductivity at high magnetic fields and a zero plateau in the Hall conductivity. Evidence for activated transport at CNP is found from the temperature dependence of the collisional conductivity.     

Grating spacing dependence of nonvolatile holographic recording with arbitrary charge transport lengths

Grating spacing dependence of nonvolatile holographic recording in doubly doped lithium niobate crystals is theoretically investigated allowing arbitrary charge transport lengths. It is shown that the nonvolatile refractive index modulation initially increases with increasing grating spacing, then a saturation behavior arises because of the dominant bulk photovoltaic effect. Although different charge transport length results in different nonvolatile refractive index modulation, the grating spacing dependence of nonvolatile holographic recording obeys almost the same rules for arbitrary charge transport lengths. The experimental results obtained by recording nonvolatile holograms in LiNbO₃:Cu:Ce crystals with different grating spacing are consistent with the theoretical analyses.     

Bulk and edge properties of the Chern-Simons Ginzburg-Landau theory for the fractional quantum Hall effect

The Chern-Simons Ginzburg-Landau theory for the fractional quantum Hall effect is studied in the presence of a confining potential We review the bulk properties of the model and discuss how the plateau formation emerges without any impurity potential. The effect is related to changes, by accumulation of charge, at the edge when the chemical potential is changed. Fluctuations about the ground state are examined and an expression is found for the velocity of the massless edge mode in terms of the confining potential. The effect of including spin is examined for the case when the system is fully polarized in the bulk. In general a spin texture may appear at the edge, and we examine this effect in the case of a small spin-down component. The low-frequency edge modes are examined and a third-order equation is found for velocities which indicates the presence of three different modes. The discussions are illustrated by numerical studies of the ground states, both for the one- and two-component cases.