金纳米线接触构型相关的双重负微分电阻与整流效应

运用第一性原理密度泛函理论(DFT)和非平衡格林函数(NEGF)方法, 研究了[111]Au纳米线与1, 4-二硫苯酚(DTB)构成的分子结的电子输运性质. 构建并优化不同的Au-DTB接触构型, 计算发现: 尖端顶位构型最利于电流输运; 非对称构型大多具有很好的整流特性(最大整流比为25.6); 部分结构出现双重负微分电阻(NDR)效应. 分析表明, 整流效应主要源于非对称接触构型两端S-Au键的稳定性差别; 尖端金原子与硫原子的耦合能级中, 近费米面的能级对低压区电子传输起主要作用; 电压增大, 离费米面较远的能级对输运起主导作用, DTB的本征能级也逐渐参与, 这一转变致使电流出现两峰一谷的双重NDR效应.     

非对称双原子分子在输运扩散中的取向效应

本文建立了同时具有化学势梯度和温度梯度的非平衡系统,研究非对称双原子分子的输运扩散行为.研究发现,双原子分子在非平衡输运中具有取向效应.浓度梯度与温度梯度使双原子分子在输运中产生的大小原子取向的方向刚好相反,沿着梯度的正方向,前者使小原子在前,后者使大原子在前.通过最小熵产生原理,解释了取向的物理机制.研究结果对于深刻理解非平衡条件下物质的输运与其形态的关系具有理论意义.     

嵌入锂原子的zigzag型单壁碳纳米管的电子传导特性

运用基于第一性原理的密度泛函理论（DFT）的非平衡格林函数（NEGF）方法对Li原子嵌入后的zigzag型单壁碳纳米管(SWCNT)的电子输运性质进行了研究.在构建和优化了Li原子嵌入的zigzag型单壁碳纳米管的电子输运模型后,研究了该系统的电子传输概率、能态密度、电子透射谱,还研究了电子能量和偏置电压设置与变化对其电子输运特性的影响.结果显示zigzag型单壁碳纳米管嵌入Li原子后,电子输运特性发生了较大变化,具有电子输运拓宽效应和量子台阶复苏效应. 关键词： Li原子 碳纳米管 电子输运 拓宽效应     

ZnSe:A1深能级的研究

为研究ZnSe中的本征缺陷和A1在ZnSe中的深能级行为,首先测量了Znse单晶体中的深能级,发现只存在Ec-0.33eV一个电子陷阱。然后,通过热扩散的方法,在300℃～700℃温度范围内把A1掺杂到ZnSe单晶体中,结果发现存在Ec-0.33eV和Ec-0.70eV两个电子陷阱。本文从缺陷化学角度对ZnSe中的本征缺陷和Ec-0.70eV深能级的结构及起源进行了讨论。     

硅纳米结构晶体管中与杂质量子点相关的量子输运

在小于10 nm的沟道空间中,杂质数目和杂质波动范围变得十分有限,这对器件性能有很大的影响.局域纳米空间中的电离杂质还能够展现出量子点特性,为电荷输运提供两个分立的杂质能级.利用杂质原子作为量子输运构件的硅纳米结构晶体管有望成为未来量子计算电路的基本组成器件.本文结合安德森定域化理论和Hubbard带模型对单个、分立和耦合杂质原子系统中的量子输运特性进行了综述,系统介绍了提升杂质原子晶体管工作温度的方法.     

经典外场驱动下Tavis-Cummings系统的能量本征值和波函数

研究经典外部驱动场对双原子Tavis-Cummings(T-C)模型中原子的作用.求出了相互作用绘景中驱动T-C系统能量——准能的本征值和相应的本征态,给出了Schrdinger绘景中该系统波函数的一般解.结果表明,外场驱动没有改变T-C模型的能级,但使该模型中的Fock态产生平移,从而使一般T-C模型中具有一定频率的定态被拓展到具有无限多个频率的Fock空间. 关键词： Tavis-Cummings模型 经典外场 能量本征值 波函数     

双频场作用下三能级原子的动力学行为

求得双频场作用下串接型三能级原子系统哈密顿量的本征函数和本征值.从而给出任意初始原子态和任意偏调情况下,原子系统随时间的演化公式.研究了能级布居数和原子极化与光强的关系.揭示了原子初始条件和光场相对相位对原子动力学行为的影响.在相对相位为π时,原子场耦合最小,在特殊情况下为零.     

C40富勒烯分子的电子结构与传输特性研究

本文采用密度泛涵理论对富勒烯C40分子进行了结构优化,得到了稳定构型,然后构建了以金原子面为电极的电子输运模型．使用非平衡格林函数方法对构建的电子输运模型进行了电子输运性质的计算,得到了电子透射谱和伏安曲线,并分析了分子器件产生电子输运性质的原因. 研究结果发现：C40富勒烯的化学活性明显强于富勒烯C60和C32分子,在一些分子能级处,该分子为一个良导体．     

C40富勒烯分子的电子结构与传输特性研究

本文采用密度泛涵理论对富勒烯C₄₀分子进行了结构优化,得到了稳定构型,然后构建了以金原子面为电极的电子输运模型.使用非平衡格林函数方法对构建的电子输运模型进行了电子输运性质的计算,得到了电子透射谱和伏安曲线,并分析了分子器件产生电子输运性质的原因.研究结果发现:C₄₀富勒烯的化学活性明显强于富勒烯C₆₀和C₃₂分子,在一些分子能级处,该分子为一个良导体.     

ZnSe：A1深能级的研究

为研究ＺｎＳｅ中的本征缺陷和Ａ１在ＺｎＳｅ中的深能级行为，首先测量了Ｚｎｓｅ单晶体中的深能级，发现只存在Ｅｅ－０．３３ｅＶ一个电子陷阱．然后，通过热扩散的方法，在３００℃～７００℃温度范围内把Ａ１掺杂到ＺｎＳｅ单晶体中，结果发现存在Ｅｅ－０．３３ｅＶ和Ｅｅ－０．７０ｅＶ两个电子陷阱．本文从缺陷化学角度对ＺｎＳｅ中的本征缺陷和Ｅｅ－０．７０ｅＶ深能级的结构及起源进行了讨论．     

光学微盘腔与三能级量子点系统中的模耦合研究

用一种全量子理论方法研究了波导、光学微盘腔与三能级量子点耦合系统的动力学过程,求出其耦合后的透射模和反射模的解析解. 由于微腔表面粗糙引起反向散射,在微腔内形成两简并回音壁耦合共振模,其耦合率为β;量子点的两激发态分别以耦合率g₁,g₂与回音壁耦合共振模产生耦合. 在实数空间里,得出透射光谱和反射光谱的数值解,这些三能级模型结果比二能级模型结果更接近真实光学微盘腔系统,能更好地显示耦合系统的动力学特性. 关键词： 模耦合 光学微盘腔 三能级量子点 全量子理论     

Single photon transport properties in coupled cavity arrays nonlocally coupled to a two-level atom in the presence of dissipation

We discuss the effects of dissipation on the behavior of single photon transport in a system of coupled cavity arrays,with the two nearest cavities nonlocally coupled to a two-level atom.The single photon transmission amplitude is solved exactly by employing the quasi-boson picture.We investigate two different situations of local and nonlocal couplings,respectively.Comparing the dissipative case with the nondissipative one reveals that the dissipation of the system increases the middle dip and lowers the peak of the single photon transmission amplitudes,broadening the line width of the transport spectrum.It should be noted that the influence of the cavity dissipation to the single photon transport spectrum is asymmetric.By comparing the nonlocal coupling with the local one,one can find that the enhancement of the middle dip of single photon transmission amplitudes is mostly caused by the atom dissipation and that the reduced peak is mainly caused by the cavity dissipation,no matter whether it is a nonlocal or local coupling case.Whereas in the nonlocal coupling case,when the coupling strength gets stronger,the cavity dissipation has a greater effect on the single photon transport spectrum and the atom dissipation affection becomes weak,so it can be ignored.     

一种新型的高频半导体量子点单电子泵

除了直流负电压外,还在浅法刻蚀出的GaAs/AlGaAs量子线上的两个金属指形门上分别叠加两个相位相差π的正弦信号,从而对形成量子点的两个势垒作不等幅调制.在无源漏偏压的情况下,通过周期形成的量子点实现了单电子的搬运.由于新的半导体量子点单电子泵不是依赖库仑阻塞效应通过隧穿进行单电子输运,因此,该器件就不会受到固定隧穿时间引起的低工作频率限制.在1.7K温度下,频率达到3GHz仍然可以观测到量子化电流平台,对应的电流值达到0.5nA量级.这种新器件提供了实现高速度、高精度搬运单电子的另一种可能途径. 关键词： 单电子输运 单电子旋转门 单电子泵 量子化电流平台     

旁耦合于介观环与铁磁电极量子点系统中的自旋极化输运

借助单杂质Anderson模型哈密顿量,及利用格林函数和运动方程等理论,研究旁耦合于介观环和铁磁电极的量子点系统中的极化输运特性.结果表明,通过调节点-环耦合强度、铁磁电极中的极化强度、磁矩相对取向及温度等,均能实现控制体系中自旋极化电流的目的,达到自旋阀效应.为此系统作为一种新的自旋电子材料提供理论依据.     

Phase coherent transmission through interacting mesoscopic systems

This is a review of the phase coherent transmission through interacting mesoscopic conductors. As a paradigm we study the transmission amplitude and the dephasing rate for electron transport through a quantum dot in the Coulomb blockade regime. We summarize experimental and theoretical work devoted to the phase of the transmission amplitude. It is shown that the evolution of the transmission phase may be dominated by non-universal features in the short-time dynamics of the quantum dot. The controlled dephasing in Coulomb-coupled conductors is investigated. Examples comprise a single or multiple quantum dots in close vicinity to a quantum point contact. The current through the quantum point contact “measures” the state of the dots and causes dephasing. The dephasing rate is derived using widely different theoretical approaches. The Coulomb coupling between mesoscopic conductors may prove useful for future work on electron coherence and quantum computing.     

Fano interference and transparency in a waveguide-nanocavity hybrid system with an auxiliary cavity

We investigate theoretically single photon transport in one-dimensional waveguide coupled to a pair of cavities, which are denoted by the first cavity and the auxiliary cavity. Two cases with no atom and one atom embedded in the first cavity are discussed. The Fano dips in the transmission spectrum and locations of transparency window are calculated. When no atom is embedded in the first cavity, there exists a transparency window under the condition that the first cavity and the auxiliary cavity are not resonant. The locations of the transparency window and Fano line type depend strongly on the eigen frequency of the auxiliary cavity and the coupling strength between the auxiliary cavity and the waveguide. When one atom is embedded in the first cavity, we show that the transparency window exists even though the first cavity, the atom and the auxiliary cavity are resonant. The Fano line type is strongly dependent on the eigen frequency of the auxiliary cavity and the coupling strength. Our results have potential applications in design of quantum devices at the level of single photon,such as single photon switch and single photon routers.     

Full counting statistics of transport electrons through a two-level quantum dot with spin–orbit coupling

We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling.     

Photon antibunching from a single quantum-dot-microcavity system in the strong coupling regime

We observe antibunching in the photons emitted from a strongly coupled single quantum dot and pillar microcavity in resonance. When the quantum dot was spectrally detuned from the cavity mode, the cavity emission remained antibunched, and also anticorrelated from the quantum dot emission. Resonant pumping of the selected quantum dot via an excited state enabled these observations by eliminating the background emitters that are usually coupled to the cavity. This device demonstrates an on-demand single-photon source operating in the strong coupling regime, with a Purcell factor of 61+/-7 and quantum efficiency of 97%.     

Control of Two-Photon Transport in a One-Dimensional Waveguide

We study the system consisting of a one-dimension waveguide side-coupled to a nonlinear cavity which was doped with a lambda-type atom and investigate the control of photons transport in one-dimension waveguide through manipulating the atom contained in the cavity. Employing the polariton technique, we show that in the single-photon case, the system behaves as a waveguide coupled to a two-level system. By solving the Schr?dinger equation, we show that single photon switch can be achieved by tuning the Rabi frequency of the classical field. In the two-photon case, the system behaves like a waveguide coupled to a cascade three-level system. Two-photon quantum correlation in the position variation can be controlled by adjusting the Rabi frequency.     

I–V characteristic of electronic transport through a quantum dot chain: The role of antiresonance

The I–V spectrum of electronic transport through a quantum dot chain is calculated by means of the nonequilibrium Green function technique. In such a system, two arbitrary quantum dots are connected with two electron reservoirs through leads. When the dot-lead coupling is very weak, a series of discrete resonant peaks in electron transmission function cause staircase-like I–V characteristic. On the contrary, in the relatively strong dot-lead coupling regime, stairs in the I–V spectrum due to resonance vanish. However, when there are some dangling quantum dots in the chain outside two leads, the antiresonance which corresponds to the zero points of electron transmission function brings about novel staircase characteristic in the I–V spectrum. Moreover, two features in the I–V spectrum arising from the antiresonance are pointed out, which are significant for possible device applications. One is the multiple negative differential conductance regions, and another is regarding to create a highly spin-polarized current through the quantum dot chain by the interplay of the resonance and antiresonance. Finally, we focus on the role that the many-body effect plays on the antiresonance. Our result is that the antiresonance remains when the electron interaction is considered to the second order approximation.