【作者】 羊富彬；

【导师】 吴绍全；

【作者基本信息】 四川师范大学 ， 理论物理， 2008， 硕士

【摘要】 作为展现低维介观体系量子效应的典型代表,量子点结构成为近年来的研究热点,由于纳米技术的进步,使人们能够在人为控制的条件下,使用量子点系统研究Fano和Kondo共振各个方面的性质,这极大地增加了人们在介观系统中研究这两个效应的兴趣。同时,T型双量子点结构在凝聚态物理学中也引起了比较大的关注和研究。对比于传统的串型和并型双量子点结构来说,T型双量子点结构显示了一些独特的性质。一方面,T型双量子点为实验有限条件下研究双杂质系统提供了可行性;另一方面,T型双量子点系统又是一个研究关联效应的模型,因为其特殊的量子点结构使得电子有了两条传输通道。一条是通过中心电子,另外一条是通过边耦合电子。此外,由于Kondo效应起源于低温稀磁合金中的磁杂质与传导电子之间的相互作用,使得Kondo效应为研究量子点局域自旋和自由臂之间的相互关联提供了一个方式。同时,Fano效应发生于电子从任意初态的两种跃迁方式(一是直接通过连续能态,或者是通过共振能态)的互相干涉。因此很有意思研究一下Fano-Kondo效应如何影响T型双量子点的传输性质。通过我们的研究结果发现,(1)当我们忽略边耦合量子点的库仑排斥,其中的一个量子点处于Kondo控制区时,我们的结果表明双量子点之间的耦合强度和边耦合量子点的相对位置对这个中心量子点的态密度和系统的线形电导都有较大的影响;而且在平衡和非平衡状态下,Kondo和Fano效应都会受到自旋极化强度的影响。(2)当我们同时考虑两个量子点的库仑排斥势时,这个系统在平衡和非平衡情况下的强弱耦合下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;此外我们还对系统的电流和微分电导是否受到自旋极化强度的变化的变化规律做了描述。我们得出的这些性质为我们研究此类T型双量子点系统提供了更多的传输性质,并且这些性质归结为系统共同存在的Fano和Kondo相互作用。T型双量子点系统是一个非常良好的双量子点结构模型,这样的一个可以包含单个和双个量子点的系统也能为研究强关联相互效应提供帮助,当然能为将来更多的自旋阀实验提供更多的可供参考的的方法。更多还原

【Abstract】 As the typical representation of exhibiting quantum effect in low dimensional mesoscopic system, the quantum dot system becomes the hot topic recently. Recent advances in nanofabrication technology have made it possible to investigate various aspects of Fano versus Kondo resonance, which has aroused new interest in the two phenomena. Meanwhile, T-shaped double-quantum-dot systems have attracted much attention in the condensed matter physics. Contrasting with the usual series and parallel DQD systems, the T-shaped DQD systems show some different properties. On the one hand, the T-shaped DQD systems provide an idea model system for studying the two impurity effects and the related experiment can be performed under controlled circumstance. On the other hand, the T-shaped DQD systems are another prototype of correlated systems, for which the special arrangement of the DQD provides two paths for the electrons to go through, one is through the central QD and the other is through the side QD. Besides, the Kondo effect arises from the interactions between a single magnetic impurity and the electrons of the bulk mental under low temperature, so the observation of the Kondo effect in QD systems opened a new path for the investigation of quantum correlation between localized spin in QD and the free lead. The Fano effect appears as a result of quantum interference between a discrete single energy level and a direct channel characterized by its continuous spectrum. It is thus interesting to study how the Kondo versus Fano effect affect the characteristic transport properties in the T-shaped DQD system. Through our study, we find the following results: (1) when the central dot is in the Kondo regime and the Coulomb interaction of the side coupled dot is not considered, it is shown that the interdot coupling and the relative position of side coupled dot levels play an essential role in the DOS and the liner conductance of central dot. There are different Kondo and Fano line shapes under the control of spin-polarized strength both in the equilibrium and nonequilibrium cases.(2) when the Coulomb interaction of the two dots is considered, the DOS of the two dots depends sensitively on the spin-polarized strength in both the equilibrium and nonequilibrium case. We also pay attention to the influence of the spin-polarized strength on the differential conductance and the current of the system. The behaviors of them provide more information about the transport properties in the T-shaped DQD system, as well as that the rich physical behavior can be attributed to the coexistence of both the Fano effect and Kondo effect. The T-shape DQD system is also a very promising quantum dot configuration. Such system involving single or multiple quantum dots may provide many opportunities for strong interaction effects, which stimulate further experimental and theoretical studies in the spintronics.更多还原