小量子点在N-S和S-S之间共隧穿的超能隙异常
Supergap anomalies in cotunneling between N-S and between S-S leads via a small quantum dot
摘要：
本文研究了在偏置电压V超过超导能隙2Δ的范围内，通过耦合到正常和超导或耦合到两个超导引线的谐振能级的共隧穿电流。由于共振能级的就地排斥，电子的共隧穿伴随着超导导线中准粒子的产生。能量守恒对这种非弹性输运通道施加了一个阈值：对于N-S情况，V_c=3Δ;对于S-S情况，\tilde{V}_c =4Δ。我们证明了电流在各自阈值附近的行为是非解析的，即δI^{in}（V）\propto（V-V_c）^{3/2}Θ（V-V_c）和δI^{in}（V）\propto（V-\tilde{V}_c）Θ（V-\tilde{V}_c）。S-S导联的强反常是能隙边缘态密度增强的结果。此外，增强的态密度使得库仑阻塞区中的双电子共隧穿过程的阈值异常比N-N引线更明显。
英文摘要：
Cotunneling current through a resonant level coupled to either normal and superconducting or to two superconducting leads is studied for the domain of bias voltages, V, exceeding the superconducting gap, 2Δ. Due to the on-site repulsion in the resonant level, cotunneling of an electron is accompanied by creation of a quasiparticle in a superconducting lead. Energy conservation imposes a threshold for this inelastic transport channel: V_c=3Δfor N-S case and \tilde{V}_c=4Δfor the S-S case. We demonstrate that the behavior of current near the respective thresholds is nonanalytic, namely, δI^{in}(V)\propto (V-V_c)^{3/2}Θ(V-V_c) and δI^{in}(V) \propto (V-\tilde{V}_c)Θ(V-\tilde{V}_c). Stronger anomaly for the S-S leads is the consequence of the enhanced density of states at the edges of the gap. In addition, the enhanced density of states makes the threshold anomalies for two-electron cotunneling processes in the Coulomb-blockaded regions more pronounced than for the N-N leads.
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