电子关联效应对T型双量子点系统的Kondo效应的影响

发布时间：2018-04-30 04:28

本文选题：T-DQD系统 + 电子关联　；参考：《四川师范大学》2015年硕士论文

【摘要】：随着纳米制备技术的发展和信息技术的需求,人们迫切希望研制出尺寸小、可靠性高的高度集成化量子器件,然而尺寸的减小将带来一系列的边界效应问题和量子效应问题。因此,为了研制出按量子力学原理工作的电子器件,人们把量子点系统的kondo效应及其对介观系统输运性质的影响作为凝聚态物理中最重要的课题之一。目前,人们做了大量的工作去研究与铁磁电极相连的T-DQD系统,其特殊的不对等结构显示出一些有趣的现象:电子可分别通过中心量子点和边耦合量子点,因此我们可以把该模型作为理想的双杂质系统去研究强关联效应。前人的研究只涉及了量子点内(忽略了点间)的库仑排斥作用对电子输运的影响和电子的自旋极化运输,因此我们有必要去研究量子点间的库仑作用、耦合强度等关联效应对电子态密度的影响。本文通过双杂质Anderson模型的哈密顿,利用隶玻色平均场技巧和运动方程方法求解了哈密顿,进而得出了量子点中电子的态密度和透射几率。通过比较不同参数下的图像,来讨论库仑排斥作用等关联效应对kondo效应的影响。研究结果表明:(1)库仑排斥作用U极大地影响了电子的态密度。在对称情况下,随U的增大,kondo共振峰的宽度变窄了,说明库仑排斥作用压制了kondo共振。这是因为在较大的库仑相互作用下,电子的双占据情况被破坏了,从而阻碍了电子的隧穿,这是间接库仑阻塞。而在非对称情况下,当U1.5时,态密度的峰宽随U的增大发生明显的变窄,之后随着U的继续增大,共振峰的峰宽竟然变宽了,这是一种特殊的变化。(2)当点间库仑作用U?0时,kondo共振峰的宽度随边耦合量子点的能级20E的增加变窄了,说明边耦合量子点的能级压制了kondo共振。而在U?1.5的情况下,当20E?2.0时共振峰的宽度随20E的增加变窄了,之后随着20E的继续增大却变宽了,这也是一种特殊的变化。(3)量子点间的耦合强度abt在弱耦合区时对kondo效应的影响不大,进入到强耦合区后对kondo共振有较大的影响,表现为kondo共振峰的宽度随abt的增大变窄了,压制了kondo共振。(4)偏压e V使kondo共振峰的峰值位置发生了偏移,并且使kondo共振峰的宽度发生了明显的变化。由于T型双量子点结构是一个可以包含单个和双个量子点的良好系统,所以我们有理由相信这些性质对T型双量子点系统在理论及应用方面的研究有着积极的指导意义。
[Abstract]:With the development of nanocrystalline preparation technology and the demand of information technology, people are eager to develop highly integrated quantum devices with small size and high reliability. However, a series of boundary effect and quantum effect problems will be caused by the reduction of size. Therefore, in order to develop electronic devices based on the principle of quantum mechanics, the kondo effect of quantum dot system and its influence on the transport properties of mesoscopic system are considered as one of the most important topics in condensed matter physics. At present, a great deal of work has been done to study the T-DQD system connected with ferromagnetic electrodes. Its special unequal structure shows some interesting phenomena: electrons can pass through central quantum dots and edge-coupled quantum dots, respectively. Therefore, we can study the strong correlation effect by using this model as an ideal double impurity system. Previous studies only deal with the effect of Coulomb repulsion on electron transport and electron spin polarization transport in quantum dots, so it is necessary to study the Coulomb interaction between quantum dots. The effect of coupling intensity and other correlation effects on the electron density of states. In this paper, the Hamiltonian of the Anderson model with double impurity is solved by using the Libose mean field technique and the equation of motion method, and the density of state and the transmission probability of the electron in the quantum dot are obtained. The effects of Coulomb exclusion and other correlation effects on the kondo effect are discussed by comparing the images with different parameters. The results show that the Coulomb repulsion U greatly affects the density of states of electrons. Under symmetric conditions, the width of kondo resonance peak becomes narrower with the increase of U, which indicates that the Coulomb repulsion suppresses the kondo resonance. This is because the double occupation of electrons is destroyed under the larger Coulomb interaction, which hinders the tunneling of electrons, which is an indirect Coulomb blocking. Under asymmetric condition, the peak width of the density of states shrinks obviously with the increase of U when U 1.5, and then with the increase of U, the width of the resonance peak becomes wider. This is a special variation. (2) when the interdot Coulomb interaction is U0, the width of the kondo resonance peak becomes narrower with the increase of the energy level 20E of the edge-coupled quantum dot, which indicates that the energy level of the edge-coupled quantum dot suppresses the kondo resonance. However, the width of the resonance peak becomes narrower with the increase of 20E and then widens with the further increase of 20E at U1. 5. This is also a special variation. The coupling intensity abt between quantum dots has little effect on the kondo effect in the weakly coupled region, but it has a great influence on the kondo resonance after entering the strong coupling region, which shows that the width of the kondo resonance peak becomes narrower with the increase of abt. Suppression of kondo resonance. 4) bias voltage EV shifts the peak position of kondo resonance peak and makes the width of kondo resonance peak change obviously. Since the structure of T-type double quantum dots is a good system which can contain single and double quantum dots, we have reason to believe that these properties have a positive guiding significance in the theoretical and practical research of T-type double quantum dot systems.
【学位授予单位】：四川师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O471.1

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