一维二元非对角关联无序体系交流跳跃电导特性

在单电子紧束缚无序模型基础上，建立了一维二元非对角关联无序体系电子跳跃输运交流电导模型，并推导了其交流电导公式，通过计算其交流电导率，探讨了格点能量无序度、格点原子组分、非对角关联及温度、外场对体系交流跳跃电导的影响.计算结果表明，一维二元非对角关联无序体系的交流电导率随格点能量无序度的增大而减小.同时，体系中两种原子的组分的变化实际代表着体系成分无序程度的变化，因而对其交流电导率的影响很大，表现为随A类原子含量p的增加而先减小后增大.当引入非对角关联时，体系出现退局域化现象，电子波函数由局 关键词： 二元无序体系 交流跳跃电导 格点能量无序度 非对角关联     

准一维多链无序体系跳跃电导特性

在单电子紧束缚近似下,建立了准一维多链无序体系直流、交流电子跳跃输运模型,通过计算探讨了无序模式、维度效应、温度及外场对其直流、交流电导率的影响.计算结果表明:准一维多链无序体系的直流、交流电导率随着格点能量无序度的增大而减小,非对角无序具有增强体系电子输运能力的作用.随着链数的增加,体系的直流、交流电导率增大,但格点能量无序度较小时,维度效应的影响不明显.在对角无序情况下准一维多链无序体系的交流电导率随温度的升高而增大,而在非对角无序模式下却随温度的升高而减小,但对于直流情况,体系的直流电导率随温度的升     

一维无序体系的交流跳跃导电

建立了electronphononfield(EPF)电子隧穿电导模型,推导了一维无序体系新的交流电导公式.通过计算具有20000—65000个格点的无序体系的交流电导率,分析了交流电导率与温度及外场频率的关系,讨论了无序度对交流电导的影响.计算结果表明,无序体系的交流电导率随外场频率的增加而近似线性的增大;无序体系在低温区出现了负微分电阻特性,电导率随温度的升高而增大,在高温区电导率随温度的升高而减小;无序度对无序体系的交流电导影响明显:在低温区,无序度越小,体系的电导率越大;在高温区,适当增大无序度, 关键词： 无序体系 电子隧穿 跳跃电导     

一维无序体系电子跳跃导电研究

建立了电子隧穿电导模型,推导了一维无序体系新的直流电导公式.通过计算20000格点无序体系的直流电导率,分析了直流电导率和温度及外场电压的关系,讨论了无序度对直流电导的影响.计算结果表明,无序体系的直流电导率随无序度的增加而减小;外加电场较小时,电导率相对较大,且出现一系列峰值,电压较大时,电导率反而较小;无序体系在低温区出现了负微分电阻特性,电导率随温度的升高而增大,在高温区电导率随温度的升高而减小.计算结果和实验符合很好 关键词： 无序体系 电子隧穿 直流电导率     

准一维纳米线电子输运的梯度无序效应

考虑实际体系的梯度无序和结散射,发展格林函数矩阵分解消元方法,研究了准一维纳米线的电子输运性质. 结果表明,由于结散射,电导随能量呈现振荡行为,无序的引入破坏了电子相干性,在低无序度区平均电导呈现异常增加,呈现一个新的电导峰. 当表面存在无序但无梯度衰减时,体系的平均电导随无序度增强先减后增,出现类局域-退局域性转变. 当表面无序线性衰减时,平均电导在强无序区稍有增加,而当表面无序高斯型衰减时,平均电导指数衰减,类局域-退局域性转变消失,不同于以前的理论预言. 研究结果对准一维纳米线电子器件的结构设计和应用有指导作用. 关键词： 准一维纳米线 梯度无序 电子输运     

准二维无序系统的电子结构

对形如N_t×N_l型准二维无序系统，只考虑格点之间的最近邻跳跃积分，采用特殊的格点编号方案，在单电子近似下，系统的哈密顿量可表示为简明对称矩阵，借助豪斯荷尔德变换将其约化为对称三对角矩阵，再利用负本征值理论及传输矩阵等方法,对系统态密度、局域长度及电导等电子结构特性进行数值计算. 重点研究了准一维四平行链和五平行链无序系统， 将结果与一维单链、准一维双链及三链系统进行对比，发现随维度的增加，系统的能带有所展宽，能态密度分布发生很大的变化，其峰值数量呈偶数规律增加. 并且在能带中心处存在有局域长度大于系统大小的扩展态，处于这些态下的系统具有较大电导. 从单链到多链，相当于扩大了系统的关联范围，使系统出现了类似非对角长程关联的行为. 关键词： 准二维无序系统 态密度 局域长度 电导     

一维无序二元固体中电子局域性质的研究

从单电子紧束缚模型的哈密顿量出发，格点能量随机取ε_A和ε_B，只计及格点之间的近程跳跃积分，建立了一维无序二元固体模型. 利用负本征值理论及无限阶微扰理论，对系统电子的本征值和本征态进行了数值计算. 结果表明与一定能量本征值对应的电子波函数只分布在系统的一定范围内，显示了其局域性. 借助传输矩阵方法，计算出电子的局域长度，讨论了局域长度随本征能量和无序度的变化关系，并研究了计入不同范围跳跃积分下，局域长度的变化特征. 关键词： 无序 二元固体 电子态 局域长度     

准一维无序系统的电子结构

利用负本征值理论的态密度计算方法，研究了准一维双链无序系统的电子结构。并针对系统大小，对角和非对角无序程等各种参数，探讨了电子的局域化，系统能量分布范围等问题。在引进无序参量后，对角无序主要引起电子局域态的增多，而非对角无序则使系统的能量分布范围发生变化。     

非对角无序和维数效应对低维无序系统电子结构的影响

运用负本征值理论，探讨了非对角无序、维数效应对低维无序系统电子结构的影响，研究表 明，非对角无序和维数效应对低维无序系统电子结构的影响很大.非对角无序主要体现出系 统的结构变化和粒子边界效应；从一维单链、准一维双链到准一维三链无序系统，电子局域 化程度加大，电子能带结构更复杂，体现出显著的维数效应. 关键词： 电子结构 低维无序系统 非对角无序 维数效应     

准一维三平行链无序系统电子结构

利用负本征值理论计算方法,重点计算出准一维平行三链无序系统的电子态密度,对比研究了一维单链、准一维双链的情况.在对角无序、非对角无序条件下,具体探讨了电子结构、局域化形成、系统能量分布及维数效应等问题.研究表明,对角无序主要引起电子局域态的增多,非对角无序则使系统的能量分布范围发生变化;通过对一维到带状系统电子结构变化的研究,观察到在相同条件下,从一维到带状系统,电子态密度的峰值数目在增加,而电子态密度为零的能量区间减少,体现出电子能带结构的维数效应.     

Direct current hopping conductance in one-dimensional diagonal disordered systems

Based on a tight-binding disordered model describing a single electron band, we establish a direct current (dc) electronic hopping transport conductance model of one-dimensional diagonal disordered systems, and also derive a dc conductance formula. By calculating the dc conductivity, the relationships between electric field and conductivity and between temperature and conductivity are analysed, and the role played by the degree of disorder in electronic transport is studied. The results indicate the conductivity of systems decreasing with the increase of the degree of disorder, characteristics of negative differential dependence of resistance on temperature at low temperatures in diagonal disordered systems, and the conductivity of systems decreasing with the increase of electric field, featuring the non-Ohm's law conductivity.     

Characteristics of alternating current hopping conductivity in DNA sequences

This paper presents a model to describe alternating current (AC) conductivity of DNA sequences, in which DNA is considered as a one-dimensional (1D) disordered system, and electrons transport via hopping between localized states. It finds that AC conductivity in DNA sequences increases as the frequency of the external electric field rises, and it takes the form of σ_ac (ω)～ω ²\ln ²(1/ω). Also AC conductivity of DNA sequences increases with the increase of temperature, this phenomenon presents characteristics of weak temperature-dependence. Meanwhile, the AC conductivity in an off-diagonally correlated case is much larger than that in the uncorrelated case of the Anderson limit in low temperatures, which indicates that the off-diagonal correlations in DNA sequences have a great effect on the AC conductivity, while at high temperature the off-diagonal correlations no longer play a vital role in electric transport. In addition, the proportion of nucleotide pairs p also plays an important role in AC electron transport of DNA sequences. For p < 0.5, the conductivity of DNA sequence decreases with the increase of p, while for p ≥ 0.5, the conductivity increases with the increase of p.     

Effect of interactions, disorder and magnetic field in the Hubbard model in two dimensions

The effects of both interactions and Zeeman magnetic field in disordered electronic systems are explored in the Hubbard model on a square lattice. We investigate the thermodynamic (density, magnetization, density of states) and transport (conductivity) properties using determinantal quantum Monte Carlo and inhomogeneous Hartree Fock techniques. We find that at half filling there is a novel metallic phase at intermediate disorder that is sandwiched between a Mott insulator and an Anderson insulator. The metallic phase is highly inhomogeneous and coexists with antiferromagnetic long-range order. At quarter filling also the combined effects of disorder and interactions produce a conducting state which can be destroyed by applying a Zeeman field, resulting in a magnetic field-driven transition. We discuss the implication of our results for experiments.     

Anderson-Mott transition driven by spin disorder: spin glass transition and magnetotransport in amorphous GdSi

A zero temperature Anderson-Mott transition driven by spin disorder can be "tuned" by an applied magnetic field to achieve colossal magnetoconductance. Usually this is not possible since spin disorder by itself cannot localize a high density electron system. However, the presence of strong structural disorder can realize this situation, self-consistently generating a disordered magnetic ground state. We explore such a model, constructed to understand amorphous GdSi, and highlight the emergence of a spin glass phase, Anderson-Mott signatures in transport and tunneling spectra, and unusual magneto-optical conductivity. We solve a disordered strong coupling fermion-spin-lattice problem essentially exactly on finite systems and account for all the qualitative features observed in magnetism, transport, and the optical spectra in this system.     

Direct current hopping conductance along DNA chain

This paper proposes a model of direct current (DC) electron hopping transport in DNA, in which DNA is considered as a binary one-dimensional disordered system. To quantitatively study the DC conductivity in DNA, it numerically calculates the DC conductivity of DNA chains with different parameter values. The result shows that the DC conductivity of DNA chain increases with the increase of temperature. And the conductivity of DNA chain is depended on the probability p, which represents the degree of compositional disorder in a DNA sequence to some extent. For p<0.5, the conductivity of DNA chain decreases with the increase of p, while for p\geq0.5, the conductivity increases with the increase of p. The DC conductivity in DNA chain also varies with the change of the electric field, it presents non-Ohm's law conductivity characteristics.     

Field-dependent charge-carrier trapping process in disordered systems

We study the diffusive spreading of excees carriers in trapping systems to which a bias electric field is applied. Since for the intermediate time range the present model appears to be identical to the electronic disordered system (the Anderson model), we have been able to derive the time and field dependencies of carrier survival probability. The results of the exact calculations obtained might provide significant insight into the transport phenomena occurring in disordered systems. It is shown that in the long-time limit the coherent potential approximation can serve as an exact solution of the problem.     

Hopping conductivity in granular systems

The model of variable-range hopping between microscopic localization centers in disordered semiconductors including Coulomb correlations is transferred to the mesoscopic situation of electron tunneling between small metal particles in granular materials. As a result we obtain for the temperature dependence of the dc conductivity well known formulas (Abeles, Mott) with certain limitations of their applicability. There is good agreement with existing experiments.