Theoretical study for the Kondo effect in the quantum transport

量子输运中近藤效应的理论研究

基本信息

批准号：
18540322
负责人：
OGURI Akira
金额：
$ 1.18万
依托单位：
Osaka City University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

(1) We studied the nonequilibrium Kondo effect in quantum dots under finite bias voltage. Specifically, we have reformulated the density matrix which describes the nonequilibrium steady state, and have obtained the reduced density matrix, by integrating out one of the two conduction channels. This formulation enables us to treat the current flowing state with a single-channel model, and may be applied to construct new nonperturbative approaches to the nonequilibrium state.(2) We have studied the Kondo effect in quantum dots connected to superconductors. In the Kondo regime where the dot has a well-defined local moment, a simple scaling argu-ment predicts that whether the ground state becomes a singlet or a magnetic doublet is determined by the value of the Kondo temperature and superconducting gap. We have pointed out that the deviation from the scaling behavior is important in quantum dots, because the Coulomb interaction and the superconducting gap can be the same order. We have shown that some important features of the deviation are seen in the superconducting atomic limit, which is realized at large gaps.(3) We have calculated the single-particle Green's function for the quantum dots connected to the superconductors, using the numerical renormalization group. Our results clarify the precise features of the Andreev bound state, which emerges inside the superconducting gap, and the density of states near the gap.(4) We have also studied the transport properties of. the super-dot-normal junctions. It is shown that the low-lying energy states can be described by a generalized version of the local Fermi-liquid theory, owing to the coupling with the normal lead. Using the numerical renormalization group, we have also calculated the renormalized parameters for the quasi-particles, and have clarified the features of the competition between the Kondo effect and the Andreev reflection.

（1）我们研究了有限偏置电压下量子点中的非平衡近代效应。具体而言，我们通过整合两个传导通道之一来重新重新制定了描述非平衡稳态的密度矩阵，并获得了降低的密度矩阵。该公式使我们能够使用单通道模型处理当前流动状态，并且可以应用于构建非平衡状态的新的非扰动方法。（2）我们研究了连接到超导体的量子点中的信息孔效应。在DOT具有明确定义的局部时刻的近藤制度中，一个简单的缩放辩论预测，基态是否变成单线或磁双线，取决于近托温度和超导间隙的值。我们指出，与缩放行为的偏差在量子点中很重要，因为库仑相互作用和超导间隙可能是相同的阶。我们已经表明，在超导原子极限中可以看到偏差的某些重要特征，该偏差在大间隙处实现。（3）我们使用数值肾功能率组计算了连接到超导体的量子点的单粒子绿色的函数。我们的结果阐明了Andreev结合状态的精确特征，该状态出现在超导间隙内，以及差距附近的状态密度。（4）我们还研究了运输特性。超点正常连接。结果表明，由于与正常铅的耦合，可以通过局部费米 - 液体理论的广义形式描述低覆能态。使用数值重新归一化组，我们还计算了准粒子的重新归一化参数，并阐明了Kondo效应与Andreev反射之间的竞争特征。