Role of coherence in resistance quantization

The quantization of resistances in the quantum Hall effect and ballistic transport through quantum point contacts is compared with the quantization of the charge relaxation resistance of a coherent mesoscopic capacitor. While the former two require the existence of a perfectly transmitting channel, the charge relaxation resistance remains quantized for arbitrary backscattering. The quantum Hall effect and the quantum point contact require only local phase coherence. In contrast quantization of the charge relaxation resistance requires global phase coherence.     

Giant charge relaxation resistance in the Anderson model

We investigate the dynamical charge response of the Anderson model viewed as a quantum RC circuit. Applying a low-energy effective Fermi liquid theory, a generalized Korringa-Shiba formula is derived at zero temperature, and the charge relaxation resistance is expressed solely in terms of static susceptibilities which are accessible by Bethe ansatz. We identify a giant charge relaxation resistance at intermediate magnetic fields related to the destruction of the Kondo singlet. The scaling properties of this peak are computed analytically in the Kondo regime. We also show that the resistance peak fades away at the particle-hole symmetric point.     

Effects of contact resistance on the evaluation of charge carrier mobilities and transport parameters in amorphous zinc tin oxide thin-film transistors

Accurate determination of the charge transport characteristics of amorphous metal-oxide transistors requires the mitigation of the effects of contact resistance. The use of additional electrodes as voltage probes can overcome contact resistance-related limitations and yields accurate charge carrier mobility values, trap depths and temperature and carrier density dependencies of mobility as well as trap depths. We show that large differences in measured charge carrier mobility values are obtained when such contact resistances are not factored out. Upon exclusion of the contact resistance, the true temperature dependence of charge carrier mobility appears in the form of two clearly distinct mobility regimes. Analyzing these revealed mobility regions leads to a more accurate determination of the underlying transport physics, which shows that contact resistance-related artefacts yield incorrect trends of trap depth with gate voltage, potentially leading to a misconstruction of the charge transport picture. Furthermore, a comparison of low- and high-mobility samples indicates that the observed effects are more general.     

Universal arrhenius temperature activated charge transport in diodes from disordered organic semiconductors

Charge transport models developed for disordered organic semiconductors predict a non-Arrhenius temperature dependence ln(mu) proportional, variant1/T(2) for the mobility mu. We demonstrate that in space-charge limited diodes the hole mobility (micro(h)) of a large variety of organic semiconductors shows a universal Arrhenius temperature dependence micro(h)(T) = micro(0)exp(-Delta/kT) at low fields, due to the presence of extrinsic carriers from the Ohmic contact. The transport in a range of organic semiconductors, with a variation in room temperature mobility of more than 6 orders of magnitude, is characterized by a universal mobility micro(0) of 30-40 cm(2)/V s. As a result, we can predict the full temperature dependence of their charge transport properties with only the mobility at one temperature known.     

Relaxation time of a chiral quantum R-L circuit

We report on the GHz complex admittance of a chiral one-dimensional ballistic conductor formed by edge states in the quantum Hall regime. The circuit consists of a wide Hall bar (the inductor L) in series with a tunable resistor (R) formed by a quantum point contact. Electron interactions between edges are screened by a pair of side gates. Conductance steps are observed on both real and imaginary parts of the admittance. Remarkably, the phase of the admittance is transmission independent. This shows that the relaxation time of a chiral R -L circuit is resistance independent. A current and charge conserving scattering theory is presented that accounts for this observation with a relaxation time given by the electronic transit time in the circuit.     

有机电致发光器件的动态电学特性

利用交流阻抗谱技术，研究了有机发光二极管ITO/Alq₃(90 nm)/Al的载流子传导机理.根据器件对不同频率的响应曲线及其等效电路模型，该器件可看作是由并联的电阻R_p和电容C_p再与电阻R_s串联而成，并根据实验数据求出了R_p，C_p和R_s的数值.实验结果表明器件的载流子传输机理属于指数分布式的陷阱电荷限制电流，其介电弛豫时间随偏压的增加而逐渐减小. 关键词： 3')" href="#">Alq₃ 陷阱电荷限制电流 交流阻抗谱 有机发光二极管     

Sample-specific and ensemble-averaged magnetoconductance of individual single-wall carbon nanotubes

We discuss magnetotransport measurements on individual single-wall carbon nanotubes (SWNTs) with low contact resistance, performed as a function of temperature and gate voltage. We find that the application of a magnetic field perpendicular to the tube axis results in a large magnetoconductance of the order of e2/h at low temperature. We demonstrate that this magnetoconductance consists of a sample-specific and of an ensemble-averaged contribution, both of which decrease with increasing temperature. The observed behavior resembles very closely the behavior of more conventional multichannel mesoscopic wires, exhibiting universal conductance fluctuations and weak localization. A theoretical analysis of our experiments will enable us to reach a deeper understanding of phase-coherent one-dimensional electronic motion in SWNTs.     

Zero-dimensional spin accumulation and spin dynamics in a mesoscopic metal island

We have measured electron spin accumulation at 4.2 K and at room temperature in an aluminum island with all dimensions (400 nm x 400 nm x 30 nm) smaller than the spin relaxation length. For the first time, we obtain uniform spin accumulation in a four-terminal lateral device with a magnitude exceeding the Ohmic resistance in the island. By controlling the magnetization directions of the four magnetic electrodes that contact the island, we have performed a detailed study of the spin accumulation. Spin precession measurements confirm the uniformity of our system and provide an accurate method to extract the spin relaxation time.     

Investigation of MWS Relaxation in Nylon 1010 using Dielectric Relaxation Spectroscopy

Maxwell–Wagner–Sillars (MWS) relaxation in nylon 1010, arising from charge carriers accumulated at the interphase between amorphous and crystalline regions, has been investigated by means of dielectric relaxation spectra. In the frequency spectra of nylon 1010, dielectric permittivity showed high values at low frequencies originating from charge carrier movement. For the MWS relaxation, the dielectric strength was independent of temperature. The results revealed that there is a transition temperature, located between 110 and 120°C, resulting in the separation of two different charge carrier movement mechanisms. Below and above this transition temperature, the temperature dependence of the MWS relaxation time follows the Vogel–Tammann–Fulcher type, showing that the charge carrier transport is governed by the motion of the polymer chains. The change of charge carrier movement mechanisms is due to the onset of polymer chain motion in the interphase.     

Spin caloritronics and the thermomagnetoelectric system

The methods of nonequilibrium thermodynamics are applied to study the transport of charge, heat and nonequilibrium spin magnetization in a discrete system comprised of a ferromagnetic metal making interfacial contact with a nonmagnetic metal. A thermomagnetic effect relating spin accumulation to an interfacial difference of temperature is described. Temperature gradients related to spin relaxation are discussed. Some recent experimental results are reviewed using the framework provided by the thermomagnetoelectric system.     

Nonlinear critical slowing down of the one-component Ginzburg-Landau field

We discuss nonlinear relaxation processes of the one-component Ginzburg-Landau field that occur near the critical point after a sudden change in temperature or in the symmetry breaking field. A universal form of the equation of motion for the order parameter at the one-loop level is derived and integrated for several cases of interest. From the results some characteristic universal amplitude ratios can be extracted.     

Dielectric study of polyaniline/poly (methylmethacrylate) composite films below the percolation threshold

We report results of dielectric relaxation studies of polyaniline/poly(methylmethacrylate) composites with polyaniline amount less than the percolation threshold in the frequency range of 0.1 Hz to 1 MHz and temperature range of 10 °C–170 °C. We find a significant dependence of the glass transition temperature Tg on the polyaniline amount in the composite. α and β relaxation processes relative to the PMMA matrix are also affected by the presence of polyaniline inclusion. We identify a relaxation process due to ionic conductivity and another process attributed to residual solvent. The characteristic relaxation frequency of each process and the activation energy depend on the polyaniline amount in the composite. The ac conductivity in the high frequency range is fitted to the universal power law of Jonscher characteristic of disordered materials.     

Effects of the surface layer of La2/3Ca1/3MnO3 thin films

The surface layer effects on transport in epitaxial La_2/3Ca_1/3MnO₃ thin films are studied. It was found that the two-probe resistance is nonlinear which is enhanced with decreasing temperature. Similar to the resistance of intrinsic La_2/3Ca_1/3MnO₃ thin films reported in the literature, the apparent dynamic contact resistance behaves semiconducting at high temperatures, passes through a peak, and displays a metallic behavior. At lowest temperatures, the curve of the contact resistance versus temperature shows a little upturn. The temperature dependent work function difference between the surface layer and the thin film underneath, together with the tunneling process across either the resulting charge depleted layer or the semiconducting surface layer is used to explain our observations.     

Correlation-induced memory effects in transport properties of low-dimensional systems

We demonstrate the remnant presence of initial correlations in the steady-state electrical current jS flowing between low-dimensional interacting leads. The leads are described as Luttinger liquids and electrons can tunnel via a quantum point contact. We derive an analytic result for the time-dependent current and show that ground-state correlations have a large impact on the relaxation and long-time behavior. In particular, the I-V characteristic is not reproduced by quenching the interaction in time. We further present a universal formula of jS for an arbitrary sequence of interaction quenches and it is established that jS is history dependent for nonsmooth switching process.     

Temperature dependence of the universal contact parameter in a unitary Fermi gas

The contact I, introduced by Tan, has emerged as a key parameter characterizing universal properties of strongly interacting Fermi gases. For ultracold Fermi gases near a Feshbach resonance, the contact depends upon two quantities: the interaction parameter 1/(k(F)a), where k(F) is the Fermi wave vector and a is the s-wave scattering length, and the temperature T/T(F), where T(F) is the Fermi temperature. We present the first measurements of the temperature dependence of the contact in a unitary Fermi gas using Bragg spectroscopy. The contact is seen to follow the predicted decay with temperature and shows how pair-correlations at high momentum persist well above the superfluid transition temperature.     

Scaling theory for percolative charge transport in disordered molecular semiconductors

We present a scaling theory for charge transport in disordered molecular semiconductors that extends percolation theory by including bonds with conductances close to the percolating one in the random-resistor network representing charge hopping. A general and compact expression is given for the charge mobility for Miller-Abrahams and Marcus hopping on different lattices with Gaussian energy disorder, with parameters determined from numerically exact results. The charge-concentration dependence is universal. The model-specific temperature dependence can be used to distinguish between the hopping models.     

冲击压缩下金属/窗口界面热弛豫过程的热阻模型研究

 研究了金属/窗口界面在冲击压缩下的热弛豫过程。从热阻模型出发，给出了弛豫时间常数与界面热阻以及材料热输运系数之间的函数关系。讨论了本文模型与Grover和Urtiew模型之间的关系。对两种不同的实验记录图像进行了解释，对产生界面热阻的原因进行了初步分析。     

Effect of electromagnetic perturbation on charge imbalance in a superconductor: A two-fluid description

Using a generalized two-fluid pictures for the charge of superconductor and ordinary Boltzmann equation for quasiparticle excitations, the effect of frequency and wave-vector dependent electromagnetic perturbation on charge imbalance near transition temperatureT _C is studied. In a situatiod where both the effective charge and distribution function of quasiparticles deviate from their equilibrium values, the charge imbalance is shown to possess a propagating solution at frequencies greater than inelastic scattering rate. In situations where charge imbalance is created by injection of quasiparticles, the charge imbalance relaxation rate is shown to decrease. We also study the effect of applied perturbation on quasiparticle diffusion length and hence on superconductor—normal interface boundary resistance.     

Interaction of anomalous muonium with electronic excitations in Si studied by longitudinal field μSR

We report longitudinal muon spin relaxation measurements in Si doped with phosphorus below room temperature. The data can be described qualitatively in a model where bond-centered muonium is undergoing spin exchange interactions below 150 K. Above this temperature, charge state cycling becomes important.This work is partially supported by the National Sciences and Engineering Research Council of Canada.