Relation between the 0.7 anomaly and the Kondo effect: Geometric crossover between a quantum point contact and a Kondo quantum dot
Relation between the 0.7 anomaly and the Kondo effect: Geometric crossover between a quantum point contact and a Kondo quantum dot
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DOI：
10.1103/physrevb.92.195401
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发表时间：
2015-11-03
影响因子：
3.7
通讯作者：
Ludwig, Stefan
中科院分区：
文献类型：
--
作者：
Heyder, Jan;Bauer, Florian;Ludwig, Stefan
量子点接触(QPC)和量子点(QD)是半导体纳米器件的两个基本构件，它们都表现出著名的反常电导特征：前者的反常为0.7，后者为近藤效应。对于0.7异常和Kondo效应，电导对温度T、源漏电压V-SD和磁场B都表现出非常相似的低能量依赖关系。在最近的一篇文章[F.Bauer等人，自然(伦敦)501，73(2013)]中，我们认为这些相似的原因是QPC和Kondo QD(KQD)都具有由样品几何形状诱导的、受限于小空间区域并通过相互作用增强的自旋涨落。在这里，我们通过研究量子点和量子点之间的几何交叉，重点研究电导对B场的依赖，从实验和理论上进一步探讨了这一概念。我们介绍了一个具有局域相互作用的一维模型，该模型再现了实验的基本特征，包括KQD和具有0.7异常的QPC之间的平稳过渡。我们发现，在这两种情况下，反常强烈的负磁电导与强烈增强的局域自旋涨落密切相关。我们的实验观察到，除了QD中的近藤效应和QPC中的0.7反常之外，在QD和QPC物理共存的区域中，Fano干涉效应，以及干净的QPC电导平台上的法布里-珀罗型共振。我们认为，如果QPC的静电势产生一个比抛物线更平的势垒顶部，一般情况下会发生法布里-珀罗型共振。
Quantum point contacts (QPCs) and quantum dots (QDs), two elementary building blocks of semiconducting nanodevices, both exhibit famously anomalous conductance features: the 0.7 anomaly in the former case, the Kondo effect in the latter. For both the 0.7 anomaly and the Kondo effect, the conductance shows a remarkably similar low-energy dependence on temperature T, source-drain voltage V-sd and magnetic field B. In a recent publication [F. Bauer et al., Nature (London) 501, 73 (2013)], we argued that the reason for these similarities is that both a QPC and a Kondo QD (KQD) feature spin fluctuations that are induced by the sample geometry, confined in a small spatial regime, and enhanced by interactions. Here, we further explore this notion experimentally and theoretically by studying the geometric crossover between a QD and a QPC, focusing on the B-field dependence of the conductance. We introduce a one-dimensional model with local interactions that reproduces the essential features of the experiments, including a smooth transition between a KQD and a QPC with 0.7 anomaly. We find that in both cases the anomalously strong negative magnetoconductance goes hand in hand with strongly enhanced local spin fluctuations. Our experimental observations include, in addition to the Kondo effect in a QD and the 0.7 anomaly in a QPC, Fano interference effects in a regime of coexistence between QD and QPC physics, and Fabry-Perot-type resonances on the conductance plateaus of a clean QPC. We argue that Fabry-Perot-type resonances occur generically if the electrostatic potential of the QPC generates a flatter-than-parabolic barrier top.