Monte Carlo simulation of electric conductivity for pure and doping fullerene (C60)

In this paper, we have used Monte Carlo (MC) method to simulate and study the temperature and doping effects on the electric conductivity of fullerene (C60). The results show that the band gap has reduced by the doping and the charge carrier transport is facilitated from valence band to conduction band by the temperature where is touched a 300 K. In this case, the conductivity reached a value of $4\times {10}^{-7}\text{S}{\text{cm}}^{-1}$. The electric conductivity of C60 can increase by the triphenylmethane dye crystal violet (CV) alkali metal to reach $4\times {10}^{-3}\text{S}{\text{cm}}^{-1}$ at 303 K. Our results of MC simulation have a good agreement with those extracted from literature [10], [33].     

最佳跳频序列族的设计与分析

本文提出了基于ｐ元广义ＧＭＷ序列和ｐ元Ｋａｓａｍｉ序列构造跳频序列族的方法,证明了基于广义ＧＭＷ序列所构造的跳频序列族具有最佳Ｈａｍｍｉｎｇ相关特性,而基于Ｋａｓａｍｉ序列所构造的跳频序列族不具有最佳Ｈａｍｍｉｎｇ相关特性。     

Interpretation of anomalous normal state optical conductivity of La-Sr-CuO cuprates

The observed frequency dependent optical response of hole doped cuprate La_1.85Sr_0.15CuO₄ superconductors, has been theoretically analysed. Starting from an effective two-dimensional (2D) interaction potential for superlattice of hole doped cuprates treated as a layered electron gas, the spectral function is formulated. Calculations of the optical conductivity σ(ω) have been made within the two-component scheme: one is the coherent Drude carriers responsible for superconductivity and the other is incoherent motion of carriers from one site to other leads to a pairing between Drude carriers. The approach accounts for the anomalies reported (frequency dependence of optical conductivity) in the optical measurements for the normal state. Estimating the effective mass from specific heat measurement and ε_∞ from band structure calculations for the low-energy charge density waves, the model has only one free parameter, the relaxation rate. The frequency dependent relaxation rates are expressed in terms of memory functions, and the coherent Drude carriers from the effective interaction potential lead to a sharp peak at zero frequency and a long tail at higher frequencies, i.e. in the infrared (IR) region. However, the hopping of carriers from one site to other (incoherent motion of doped carriers) yields a peak value in the optical conductivity centred at mid-IR (MIR) region. We find that both the Drude and hopping carriers in the superlattice of cuprates will contribute to the optical process of conduction in the CuO₂ planes and shows similar results on optical conductivity in the MIR as well as IR frequency regions as those revealed from experiments.     

Magnetoconductivity of Hubbard bands induced in silicon MOSFETs

Sodium impurities are diffused electrically to the oxide-semiconductor interface of a silicon MOSFET to create an impurity band. At low temperature and at low electron density, the band is split into an upper and a lower sections under the influence of Coulomb interactions. We used magnetoconductivity measurements to provide evidence for the existence of Hubbard bands and determine the nature of the states in each band.     

Hopping Transport and Stochastic Dynamics of Electrons in Plasma Layers

We investigate the stochastic dynamics and the hopping transfer of electrons embedded into two‐dimensional atomic layers. First we formulate the quantum statistics of general atom ‐ electron systems based on the tight‐binding approximation and express ‐ following linear response transport theory ‐ the quantum‐mechanical time correlation functions and the conductivity by means of equilibrium time correlation functions. Within the relaxation time approach an expression for the effective collision frequency is derived in Born approximation, which takes into account quantum effects and dynamic effects of the atom motion through the dynamic structure factor of the lattice and the quantum dynamics of the electrons. In the last part we derive Pauli equations for the stochastic electron dynamics including nonlinear excitations of the atomic subsystem. We carry out Monte Carlo simulations and show that mean square displacements of electrons and transport properties are in a moderate to high temperature regime strongly influenced by by soliton‐type excitations and demonstrate the existence of percolation effects (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear transport in p-type SiGe quantum well structure containing Ge quantum dots

We use magneto-transport spectroscopy to study a dramatic instability between a low and high conductivity mode in Si/SiGe-based resonant tunneling diodes with an embedded layer of self-assembled Ge hut cluster quantum dots in the Si barrier. In the low current regime a simple activation-type behavior with an astonishingly low activation energy in the order of 0.1 meV is determined. In the high current regime a region of negative differential conduction can be observed. We discuss the influence of different layer structures and magnetic fields.     

The effect of increasing the excitation level of the sodium atom on the structure of the NaArn polyatomic exciplexes

In this work, the geometrical structures, the formation energies, and electronic states of the Na(ms)Ar_n polyatomic exciplexes with m = 3-6 and n = 2-5 are studied by using a quantum-classical method. The interaction potential between an electronically excited sodium atom and argon atoms are calculated by using a one-electron model involving electron-Ar and electron-Na⁺ pseudopotentials, in which the Hamiltonian is diagonalized at every optimization step in the Basin Hopping algorithm. The relationship between the position of the electronically excited levels and the cluster geometry is investigated as a function of the excitation level and of the spatial extension of the excited electron orbital. We show that the equilibrium structures of the ground state Na(3s)Ar_n and those of the electronically excited states Na(4s)Ar_n, Na(5s)Ar_n, and Na(6s)Ar_n are significantly different. As a result of the detailed examination of the relationships between the geometrical structure and density distribution of the Na valence electron of the Na^∗Ar_n with n = 2-5 polyatomic exciplexes, we can see that for the Na(4s)Ar_n polyatomic exciplexes, the two extreme geometries, neutral Na(3s)Ar_n and ionic Na⁺Ar_n compete. It appears that none of them is the actual one. For Na(5s)Ar_n and Na(6s)Ar_n the valence electron is very weakly bound to the ionic core and described by a more diffused orbital so that the geometry and the formation energies of this excited state called Rydberg states converge towards those of the ionic cores.     

Hopping Wave Function in Quantum Kicked Systems

A model of a kicked particle in an infinite potential well is studied. We presented the wave functions of the system applying a direct perturbation method. Theoretical analyses and numerical calculations show that the wave function is discontinuous across each kicking instant. As an extension of this result, we find that the wave function of any periodically kicked system usually has this property. Therefore, at each kicking instant, the wave function chooses randomly between the limits on either side and may be hopping.     

分子马达的三态周期跳跃模型

研究了在一维三态周期跳跃模型下分子马达的定向运动.对于给定的任意初始分布,得出了与时间有关的几率分布的解析表达式,包括到达稳态之前的所有的瞬态过程,由此可获得马达在各个时刻的漂移速度v、扩散系数D以及描述马达随机性质的随机参数r(randomness parameter ).同时还计算了马达到达稳态所需要的特征时间.并把计算结果同实验进行了比较.     

隧道结电场辅助下叔丁胺分子在Cu(111)表面跳跃(英文)

采用扫描隧道显微镜(STM)于78 K研究了单个叔丁胺分子在Cu(111)表面的横向跃迁现象.研究发现叔丁胺分子的跳跃几率随隧道电流的增加而线性增加,这表明该过程是单电子激发过程;在不同极性的隧道结电场作用下,叔丁基胺分子跳跃行为发生的几率不同,这种现象可以用电场辅助的扩散过程解释.在不同极性电场作用下叔丁胺分子在Cu(111)表面的吸附能和扩散势垒不同,从而表现出不同的跳跃几率.