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     

Giant Persistent Current in a Mesoscopic Ring with Parallel-Coupled Double Quantum Dots

We theoretically study the properties of the ground state of the parallel-coupled double quantum dots embedded in a mesoscopic ring in the Kondo regime by means of the two-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. Our results show that in this system, the persistent current depends sensitively on both the parity of this system and the size of the ring. Two dots can be coupled coherently, which is reflected in the giant current peak in the strong coupling regime. This system might be a candidate for future device applications.     

Fano--Kondo Effect in a Triple Quantum Dots Coupled to Ferromagnetic Leads

Using the Keldysh nonequilibrium Green function and equation-of-motion technique, we have qualitatively studied the spin-dependent transport of a triple-QD system in the Kondo regime. It is shown that the Kondo resonance and Fang interference coexist, and in this system the Fang Kondo effect shows dip behaviours richer than that in the T-shaped QDs. The interdot coupling, the energy level of the side coupled QDs and the spin polarization strength greatly influence the DOS of the central quantum dot QDo. Either the increase of the coupling strength between the two QDs or that of the energy levels of the side coupled QDs enhances the Kondo resonance. Especially, the Kondo resonance is strengthened greatly when the side dot energy is fixed at the Fermi energy. Meanwhile, the Kondo resonance splits for the spin-up and spin-down configurations due to the polarization： the down-spin resonance is enhanced, and the up-spin resonance is suppressed.     

嵌入耦合量子点的介观A-B环内的持续电流

使用双杂质的Ansderson模型的哈密顿 ,从理论上研究了一个嵌入并联耦合量子点(DQD)的介观A -B环系统处在Kondo区时的基态性质 ,并用slave boson平均场方法求解了哈密顿。结果表明 ,在这个系统中 ,由磁通诱导而产生的持续电流依赖于系统的宇称效应和尺寸大小 ,并随隧穿耦合强度的增加而变得越来越复杂。在δ >T0 K 时 ,它的电流的峰值是奇宇称的大于偶宇称的 ,并随隧穿耦合强度的增加而增大 ,但Fano共振却被削弱 ,系统始终存在宇称效应 ,这个系统与单 (串联耦合双 )量子点系统相比 ,有许多不同的物理性质。因此 ,在未来的装置设计中 ,是很有潜力的。     

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.     

Spin-dependent transport through an interacting quantum dot system

Using an equation of motion technique, we report on a theoretical analysis of transport characteristics of a spin-valve system formed by a quantum dot coupled to ferromagnetic leads, whose magnetic moments are oriented at an angle θ with respect to each other, and a mesoscopic ring by the Anderson Hamiltonian. We analyse the density of states of this system, and our results reveal that the density of states show some noticeable characteristics depending on the relative angle θ of magnetic moment M, and the spin-polarised strength P in ferromagnetic leads, and also the magnetic flux Φ and the number of lattice sites N_R in the mesoscopic ring. These effects might have some potential applications in spintronics.     

Magnetotransport through an Aharonov-Bohm ring with parallel double quantum dots coupled to ferromagnetic leads

Using the Keldysh nonequilibrium Green function and equation-of-motion technique, this paper studies the magnetotransport through an Aharonov--Bohm (AB) ring with parallel double quantum dots coupled to ferromagnetic leads. It calculates the transmission probability in both the equilibrium and the nonequilibrium case, analyses the conductance and the tunnel magnetoresistance for various parameters, and obtains some new results. These results show that this system is provided with an excellent spin filtering property, and that a large tunnelling magnetoresistance and a negative tunnelling magnetoresistance can arise by adjusting relative parameters; these facts indicate that this system is a possible candidate for spin valve transistors, and has important applications in spintronics.     

Kondo and Coulomb Interaction Effects in Spin-Polarized Transport through Double Quantum Dots

By means of the slave-boson mean-field approximation, we theoretically investigate the Kondo and Coulomb interaction effects in spin-polarized transport through two coupled quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. The density of states is calculated in the Kondo regime for the effect of the interdot Coulomb repulsion with both parallel and antiparallel lead-polarization alignments. Our results reveal that the interdot Coulomb interaction between quantum dots greatly influence the density of states of the dots.     

嵌入单量子点Aharonov-Bohm环中的近藤效应

使用单杂质的Ansderson模型, 从理论上研究了一个嵌入单量子点Aharonov-Bohm环系统处在 近藤区时的基态性质, 并用slave-boson平均场方法求解了该模型.结果表明：在零温, 当介 观环内电子平均能级间隔大于近藤关联能时, 系统内仍然存在一个被减弱了的近藤效应；系 统的基态性质依赖于系统的宇称和环的大小；而尺寸效应和近藤屏蔽效应的共存导致了系统 丰富的物理性质.同时, 可以通过测量介观环中的持续电流和杂质磁化率, 达到探测近藤屏 蔽云的目的. 关键词： 持续电流 杂质磁化率 宇称效应 近藤效应 近藤屏蔽云