【作者】 李华；

【导师】 吕天全；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2006， 博士

【摘要】 量子点是继超晶格和量子阱之后,于上个世纪80年代中后期和量子线同时发展起来的一种新型低维量子结构。几个量子点在空间上相互靠近并发生耦合效应就形成了耦合量子点体系。对于耦合量子点体系,无论其组成的量子点的空间对称性,还是量子点的尺寸、相互之间的耦合强度都是人为可以调控的,从而实现了人们操纵固体的梦想,并因此而受到广泛的关注。本文采用非平衡格林函数方法,对几种新型的耦合量子点结构的输运性质进行了系统的理论研究,并得到了一些有意义的结果。首先,我们研究了环形量子点阵列（简称量子点环）与两个电极相耦合形成的两终端体系的输运性质。对于量子点环而言,与电极相耦合的量子点在环中占有特殊的地位。因此我们分别讨论了两个电极与环中的同一个量子点相耦合、两个电极分别与环中相邻的两个量子点相耦合以及两个电极分别与环中不相邻的两个量子点相耦合的三种结构。利用非平衡格林函数的运动方程和Dyson方程,分别在三种结构中推导了当体系包含任意个量子点时的电流递推表达式,它们均可以写成统一的类Landauer-Büttiker公式形式。在数值计算部分,作为体系的一个特例,我们首先详细的研究了由四个量子点耦合成的量子点环中的电子输运,确定了三种结构的共振隧穿谱线对单量子点能级的不同组合情况以及相邻量子点之间的耦合强度的依赖关系。随着量子点数目的增多,体系的共振隧穿谱会变得更加复杂。因此在对由n个量子点耦合成的量子点环的数值计算中,我们假定所有的量子点都是全同的,即所有的量子点都具有相同的单量子点能级ε_i⁰ =ε₀,并且相邻量子点之间的耦合强度都相等,即V_{i , i+1} = V₀。计算结果表明,三种结构的的输运性质差别很大。对于两个电极和量子点环中的同一个量子点相耦合的结构,共振隧穿谱中的每个共振峰的峰值都相等,并且都取最大值1.0。当n为偶数时,体系共振隧穿谱关于ε₀对称分布,其中的共振峰的数目等于n /2 + 1个。并且随着n /2奇偶性的变化而在ε₀处表现出明显的奇偶性,即:当n /2为偶数时,在ε₀处出现电子可以隧穿通过的共振峰;而n /2为奇数时,在ε₀处没有共振峰出现;我们把这种奇偶性成为“半奇偶性”,这与一维量子点阵中的奇偶性正好相反。当n为奇数时,体系的共振隧穿谱没有对称性,而共振峰更多还原

【Abstract】 Quantum dot is a new kind of low-dimensional quantum structure, which, together with quantum wire, is developed after superlattices and quantum well in the late 80’s of last the century. Several quantum dots form a coupled-quantum-dot system when they close up and couple to each other by tunnel coupling. For coupled-quantum-dot systems, no matter the spatial symmetry, size and tunnel coupling strength between quantum dots are all controllable. In this way, the dream of controlling solids is realized. For this reason, the transport properties of systems consisting mutiple quantum dots have attracted the interest of physicists. In this thesis, by making use of the nonequilibrium Green’s function technique, we investigated the transport properties of several new kinds of coupled-quantum-dot systems theoretically and obtained several significant results.First, we report a theoretical study of an ideal ring-shaped array of quantum dots (quantum-dot ring for short) in a two-terminal configuration. For a quantum-dot-ring, the dots connected to the leads are special than the others. So we discuss three different configurations with the two leads being connected to the same dot, to two adjcent dots, and to two unadjcent dots. By making use of the equation of motion and Dyson equation of Green’s functions, we have developed a theoretical method for a quantum-dot ring with arbitary number of dots. As an example, we numerically investigated the transport properties of a four-quantum-dot ring. We found that the resonant tunneling spectrum depends on the arrangement of the single-dot energy level, the interdot tunnel coupling amplitude between neighbouring dots, and the tunnel coupling between dots and leads. The study shows that all these parameters have strong influence to the transport properties of the system.With the increasing of the number of dots, the resonant tunneling spectrum becomes more complex. When we disscuss the n-dot system, for simplicity, we assume all quantum dots are all equivalent, i.e. all the single-dot energy levels are更多还原