Kondo screening of Andreev bound states in a normal metal-quantum dot-superconductor system
Kondo screening of Andreev bound states in a normal metal-quantum dot-superconductor system
复制标题
普通金属-量子点-超导体系统中安德烈夫束缚态的近藤筛选
DOI：
10.1103/physrevb.94.165144
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发表时间：
2016-10
影响因子：
3.7
通讯作者：
Chen Wei-Qiang
中科院分区：
文献类型：
--
作者：
Li Lin;Cao Zhan;Fang Tie-Feng;Luo Hong-Gang;Chen Wei-Qiang
基于对近藤增强的安德列夫输运的实验观察[R.S.Deacon等人，Phys.B81,121308(R)(2010年)]在混合正常金属-量子点-超导体(N-QD-S)器件中，我们从理论上研究了这种器件中的近藤效应，阐明了正常引线和超导引线所起的不同作用。由于QD-S系统中的安德烈夫反射，在超导禁带中形成了一对安德烈夫能级，如果QD的基态是二重态，则该能级能够携带磁矩。从这个意义上说，Andreev能级起到了有效杂质能级的作用。当正常的铅与QD-S系统耦合时，一方面，安德烈夫能级展宽，形成所谓的安德烈夫束缚态；另一方面，它可以屏蔽束缚态的磁矩。通过调节量子点和正常(超导)引线之间的耦合，ABSS可以模拟通常的单杂质Anderson模型的近藤、混合价甚至空轨道区域。上面的图像被N-QD-S混合模型的格林函数计算所证实，也能够定性地解释Deacon等人观察到的实验现象。这些结果可以进一步推动N-QD-S体系的相关实验研究。
Motivated by experimental observation of the Kondo-enhanced Andreev transport [R. S. Deacon et al., Phys. Rev. B 81, 121308(R) (2010)] in a hybrid normal metal-quantum dot-superconductor (N-QD-S) device, we theoretically study the Kondo effect in such a device and clarify the different roles played by the normal and superconducting leads. Due to the Andreev reflection in a QD-S system, a pair of Andreev energy levels form in the superconducting gap, which is able to carry the magnetic moment if the ground state of the QD is a magnetic doublet. In this sense, the Andreev energy levels play a role of effective impurity levels. When the normal lead is coupled to the QD-S system, on the one hand, the Andreev energy levels broaden to form the so-called Andreev bound states (ABSs); on the other hand, it can screen the magnetic moment of the ABSs. By tuning the couplings between the QD and the normal (superconducting) leads, the ABSs can simulate the Kondo, mixed-valence, and even empty orbit regimes of the usual single-impurity Anderson model. The above picture is confirmed by the Green's function calculation of the hybrid N-QD-S Anderson model and is also able to explain qualitatively experimental phenomena observed by Deacon et al. These results can further stimulate related experimental study in the N-QD-S systems.