arXiv 0712.22522007-12-13cond-mat.mes-hallcond-mat.supr-con

Andreev干涉仪的宏观共振调谐

Macroscopic Resonant Tunneling through Andreev Interferometers

M. C. Goorden, Ph. Jacquod, J. Weiss

发表信息：: Nanotechnology 19, 135401 (2008)
DOI：: 10.1088/0957-4484/19/13/135401

摘要：

研究了两个s波超导体上的弹道混沌量子点的电导和光谱随两个序参量之间的相位差$ϕ$的变化.结合分析技术-随机矩阵理论，纳扎罗夫的电路理论和基于量子力学的半经典理论-使我们能够详细探索量子到经典的交叉。当超导体没有相位偏置时，$ϕ=0$，我们恢复已知的结果，即量子点的光谱表现出激发间隙，而通过两个正常的引线携带$N_{\rm N}$通道和连接到点通过隧道接触的透明度$Γ_{\rm N}$的电导是$\propto Γ_{\rm N}^2 N_{\rm N}$。相反，当$ϕ=π$时，激发能隙关闭，电导变为通用状态下的$G \propto Γ_{\rm N} N_{\rm N}$。对于$Γ_{\rm N} \ll 1$，我们观察到一个数量级的电导增强对$G \propto N_{\rm N}$在短波长的限制。我们将这种增强与通过接近费米能量的宏观数量的能级的共振隧穿联系起来。我们的预测得到了数值模拟的证实。

英文摘要：

We investigate the conductance through and the spectrum of ballistic chaotic quantum dots attached to two s-wave superconductors, as a function of the phase difference $ϕ$ between the two order parameters. A combination of analytical techniques -- random matrix theory, Nazarov's circuit theory and the trajectory-based semiclassical theory -- allows us to explore the quantum-to-classical crossover in detail. When the superconductors are not phase-biased, $ϕ=0$, we recover known results that the spectrum of the quantum dot exhibits an excitation gap, while the conductance across two normal leads carrying $N_{\rm N}$ channels and connected to the dot via tunnel contacts of transparency $Γ_{\rm N}$ is $\propto Γ_{\rm N}^2 N_{\rm N}$. In contrast, when $ϕ=π$, the excitation gap closes and the conductance becomes $G \propto Γ_{\rm N} N_{\rm N}$ in the universal regime. For $Γ_{\rm N} \ll 1$, we observe an order-of-magnitude enhancement of the conductance towards $G \propto N_{\rm N}$ in the short-wavelength limit. We relate this enhancement to resonant tunneling through a macroscopic number of levels close to the Fermi energy. Our predictions are corroborated by numerical simulations.

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