平行耦合双量子点分子A-B干涉仪的电荷及其自旋输运

利用非平衡格林函数方法,理论研究每臂中嵌有一个平行耦合双量子点分子的A-B干涉仪(平行耦合双量子点分子A-B干涉仪)的电荷及其自旋输运性质.无外磁场时,与每臂中嵌有一个量子点的A-B干涉仪相比较,平行耦合双量子点分子A-B干涉仪中电子隧穿变得更加容易发生.当平行耦合双量子点分子A-B干涉仪中引入外磁场时,能够在电导能谱中观察到一个Fano共振和一个反共振,这两种输运状态在磁场取适当数值时能够同时消失.此外,通过调节左右两电极间的偏压、磁通和Rashba自旋轨道相互作用,可以对体系自旋输运进行调控.     

两端线型双量子点分子Aharonov-Bohm干涉仪电输运

设计一个两端线型双量子点分子Aharonov-Bohm (A-B)干涉仪. 采用非平衡格林函数技术, 理论研究无含时外场作用下的体系电导和引入含时外场作用下的体系平均电流. 在不考虑含时外场时, 调节点间耦合强度或磁通可以诱导电导共振峰劈裂. 控制穿过A-B干涉仪磁通的有无, 实现了共振峰电导数值在0与1之间的数字转换, 为制造量子开关提供了一个新的物理方案. 同时借助磁通和Rashba自旋轨道相互作用, 获得了自旋过滤. 当体系引入含时外场时, 平均电流曲线展示了旁带效应. 改变含时外场的振幅, 实现了体系平均电流的大小与位置的有效控制, 而调节含时外场的频率, 则可以实现平均电流峰与谷之间的可逆转换. 通过调节磁通与Rashba自旋轨道相互作用, 与自旋相关的平均电流亦得到有效控制. 研究结果为开发利用耦合多量子点链嵌入A-B 干涉仪体系电输运性质提供了新的认知. 上述结果可望对未来的量子器件设计与量子计算发挥重要的指导作用.     

T型耦合双量子点系统的非对等Kondo共振分裂传输

利用隶玻色子平均场近似理论,并借助于单杂质的Anderson模型的哈密顿量,研究了T型耦合双量子点嵌入正常电极的基态输运性质.结果表明：在体系处于平衡状态时,随着双量子点的耦合强度增加,体系的Kondo 效应被削弱. 当耦合强度足够强时,Kondo量子点态密度的Kondo共振单峰分裂成两个不对等的Kondo共振双峰.在体系处于非平衡状态时,增加两电极的偏压,态密度的Kondo分裂的非对等性明显加强. 关键词： Kondo效应 态密度 格林函数法 耦合双量子点     

量子点环嵌入Aharonov-Bohm干涉器中电子的退耦合态及反共振现象

采用Anderson模型哈密顿量和非平衡态格林函数方法对量子点环以不同构型嵌入A-B干涉器中电子输运的退耦合态及反共振现象进行了理论研究. 结果表明,量子点环A-B干涉器的结构对称性以及穿过A-B干涉器的磁通量是诱发退耦合现象的两种物理机理. 耦合量子点结构的对称性越高,体系在相干电子输运过程中表现出来的退耦合及反共振现象越明显. 而且在具有高度对称性的耦合量子点结构中,通过磁场调节体系的结构参数可以分别使第奇数或第偶数分子本征态从电极上退耦合,从而使电子输运电导表现出奇偶对等振荡现象. 这为设计纳米电子开关器件提供了一个新的物理模型. 关键词： 量子点环 A-B干涉器 退耦合 反共振     

量子点双链中电子自旋极化输运性质

利用非平衡格林函数方法, 研究了与单个量子点耦合的量子点双链中电子自旋极化输运性质. 由于系统中Rashba自旋轨道耦合产生的自旋相关的相位, 电子通过上下两种路径时, 自旋不同的电子干涉情况不同, 从而导致了电极中的自旋极化流. 左右两电极间的偏压使单个量子点中的自旋积聚在很大能量区域内能够保持较大的值. 由于系统结构的左右不对称, 正负偏压下自旋积聚情况完全不同. 这些计算结果将有助于实验上设计新型的自旋电子学器件.     

T型双量子点自旋极化输运

采用Keldysh非平衡态格林函数方法和运动学方程方法,我们研究了耦合于铁磁极的T型双量子点自旋极化输运。研究发现由于Kondo效应和Fano效应的共同作用,在平衡和非平衡情况下,系统的态密度都随着铁磁电极的自旋极化强度的变化而发生变化,这样的一个可以包含单个和双个量子点的系统能为将来自旋阀实验上的进步提供更多的可供参考的的方法。     

点间耦合强度对三耦合量子点系统微分电导的影响

本文利用非平衡格林函数运动方程方法,研究了与两个电极耦合在一起的三耦合量子点系统的微分电导及量子干涉的AB振荡问题.通过理论计算发现,由于量子点上的局域态密度的不同从而导致系统电导或隧穿性质的不同,而且量子点间耦合强度、量子点能级等都会对输运性质产生影响. 关键词： 量子点 非平衡格林函数 运动方程 局域态密度     

量子点环的电子输运研究

利用非平衡格林函数方法，研究了量子点环的相干输运性质. 结果表明：与一维量子点阵列 相比，量子点环中的电子出现更多新的准束缚能级. 量子点间耦合的增强会使微分电导振荡 出现退相干现象. 关键词： 量子点 电导     

低维纳米材料量子热输运与自旋热电性质 ——非平衡格林函数方法的应用

低维材料不断涌现的新奇性质吸引着科学研究者的目光. 除了电子的量子输运行为之外, 人们也陆续发现和确认了热输运中显著的量子行为, 如 热导低温量子化、声子子带、尺寸效应、瓶颈效应等. 这些小尺度体系的热输运性质可以很好地用非平衡格林函数来描述. 本文首先介绍了量子热输运的特性、声子非平衡格林函数方法及其在低维纳米材料中的研究进展; 其次回顾了近年来在 一系列低维材料中发现的热-自旋输运现象. 这些自旋热学现象展现了全新的热电转换机制, 有助于设计新型的热电转换器件, 同时也给出了用热产生自旋流的新途径; 最后介绍了线性响应理论以及在此理论框架下结合声子、电子非平衡格林函数方法进行的一些有益的探索. 量子热输运的研究对热效应基础研究以及声子学器件、能量转换器件的发展有着不可替代的重要作用.     

通过嵌入铁磁电极之间 Aharonov-Bohm 干涉仪自旋极化输运性质的研究

使用非平衡态格林函数方法和运动方程近似,研究了嵌入铁磁电极之间Aharonov-Bohm 干涉仪的自旋极化输运性质.在左右铁磁电极平行和反平行两种磁组态下,结合Fano因子分析和讨论了Fano 和Kondo 共振对该系统电导的影响,以及电导随自旋极化强度和磁通的变化.结果表明,自旋极化强度和磁通能有效地调节和控制电导,但电导的线形主要由磁通决定;在适当的条件下能导致大的正磁阻和负磁阻的出现.因此,该系统是一个很好的自旋阀晶体管,在自旋电子学中有潜在的应用价值. 关键词： Fano和Kondo共振 自旋极化强度 Fano因子 隧道磁阻     

Photon-assisted electronic and spin transport through two T-shaped three-quantum-dot molecules embedded in an Aharonov-Bohm interferometer

We investigate the time-modulated electronic and spin transport properties through two T-shaped three-quantum-dot molecules embedded in an Aharonov-Bohm(A-B) interferometer. By using the Keldysh non-equilibrium Green's function technique, the photon-assisted spin-dependent average current is analyzed. The T-shaped three-quantum-dot molecule A-B interferometer exhibits excellent controllability in the average current resonance spectra by adjusting the interdot coupling strength, Rashba spin-orbit coupling strength, magnetic flux, and amplitude of the time-dependent external field.Efficient spin filtering and multiple electron-photon pump functions are exploited in the multi-quantum-dot molecule A-B interferometer by a time-modulated external field.     

Spin Accumulation in a Double Quantum Dot Aharonov-Bohm Interferometer

We investigate the spin accumulation in a double quantum dot Aharonov-Bohm （AB） interferometer in which both the Rashba spin-orbit （RSO） interaction and intradot Coulomb interaction are taken into account. Due to the existence of the RSO interaction, the electron, flowing through different arms of the AB ring, will acquire a spin-dependent phase factor in the tunnel-coupling strengths. This phase factor will induce various interesting interference phenomena. It is found that the electrons of the different spin directions can accumulate in the two dots by properly adjusting the bias and the intradot level with a fixed RSO interaction strength. Moreover, both the magnitude and direction of the spin accumulation in each dot can be conveniently controlled and tuned by the gate voltage acting on the dot or the bias on the lead.     

Spin-Dependent Electron Properties of a Triple-Terminal Quantum Dot Structure

Electron transport properties of a triple-terminal Aharonov-Bohm interferometer are theoretically studied. By applying a Rashba spin-orbit coupling to a quantum dot locally, we find that remarkable spin polarization comes about in the electron transport process with tuning the structure parameters, i.e., the magnetic flux or quantum dot levels. When the quantum dot levels are aligned with the Fermi level, there only appear spin polarization in this structure by the presence of an appropriate magnetic flux. However,in absence of magnetic flux spin polarization and spin separation can be simultaneously realized with the adjustment of quantum dot levels, namely, an incident electron from one terminal can select a specific terminal to depart from the quantum dots according to its spin state.     

Transmission through a quantum dot molecule embedded in an Aharonov-Bohm interferometer

We study theoretically the transmission through a quantum dot molecule embedded in the arms of an Aharonov-Bohm four quantum dot ring threaded by a magnetic flux. The tunable molecular coupling provides a transmission pathway between the interferometer arms in addition to those along the arms. From a decomposition of the transmission in terms of contributions from paths, we show that antiresonances in the transmission arise from the interference of the self-energy along different paths and that application of a magnetic flux can produce the suppression of such antiresonances. The occurrence of a period of twice the quantum of flux arises at the opening of the transmission pathway through the dot molecule. Two different connections of the device to the leads are considered and their spectra of conductance are compared as a function of the tunable parameters of the model.     

Electronic spin precession and interferometry from spin-orbital entanglement in a double quantum dot

A double quantum dot inserted in parallel between two metallic leads can entangle the electron spin with the orbital (dot index) degree of freedom. An Aharonov-Bohm orbital phase can be transferred to the spinor wave function, providing a geometrical control of the spin precession around a fixed magnetic field. A fully coherent behavior occurs in a mixed orbital-spin Kondo regime. Evidence for the spin precession can be obtained, either using spin-polarized metallic leads or by placing the double dot in one branch of a metallic loop.     

Optically mediated spin current and Fano resonance in an Aharonov-Bohm ring with a quantum dot

We study the spin-polarized transport and Fano resonance in an Aharonov-Bohm (AB) interferometer with an embedded quantum dot, where the dot is irradiated by continuous circularly polarized light. Compared with the conventional Fano form, the resonance line shape is found to be deformed by the interplay between the external irradiation and the Coulomb repulsion. The Fano resonance peaks are split due to the shift of the effective energy level in the dot by Rabi oscillation of electron-heavy hole pairs. The direction and magnitude of spin current polarization can be modulated by the device parameters. Furthermore, the direct tunneling between two leads can induce a sharp sign reversal of spin polarization, the system thus operates as a rectifier for spin current polarization.     

Phase Interference in a Multi-level Quantum-Dot System

Considering phase interference, we investigate coherent transport in a quantum dot by using a thermopower. In the single process of the electronic transport through the quantum dot, it is shown that the phase interference between the levels of a quantum dot is like the Aharonov-Bohm effect. The result indicates that the thermopower is very sensitive to phase interference. It is also found that the phase-difference change of the different levels of the quantum dot can determine the shape of the thermopower.