Study on Submilimeterwave Spectroscopy of Superconducting quasi-one-dimensional Quantum Wires

本文报道了超导-收缩-超导（S-c-S）准一维介观器件中输运噪声的性质和射频特性的实验结果。这些器件是通过在液氦（4.2K）中向绝缘Nb/Insulator/Nb（或NbN）夹层施加电压脉冲来制造的。用这种方法，我们可以连续地改变准粒子的电流-电压（I-V）曲线，从绝缘体到隧道接触，最后到理想的金属导电界面。我们发现，I，dV/dI与V的关系曲线与Blonder，Tinkham和Klapwijk（BTK）理论和Octabio和BTK（OTBK）理论的预测值很接近。我们还发现，噪声电压功率谱密度Sv（f）随着器件品质因数Q^的增加而快速下降，<-1>并且当Q^ &gt;2时饱和<-1>。这种饱和表明，在理论模型（Hooge模型）的框架内，收缩区附近与缺陷相关的载流子数在Q^<-1>&gt;2的情况下不再变化。在我们的样品中，仅在干净的金属器械中观察到清晰的周期性dV/dI峰。间隙电压以上的这些周期性dV/dI峰值的起源可能与量子尺寸效应或几何共振模型相关联，该几何共振模型考虑了收缩中的态密度的量子化。新的微波诱导的步骤中观察到的微波辐照的器件的电流-电压特性。观察到的步骤是不同于著名的“夏皮罗步骤”的功能。这种微波引起的步骤的整体特征不能使用现有的模型来解释。虽然这些峰的起源尚不清楚，但这种现象的一个可能的起源是微波场与收缩中的Andreev反射电子/空穴的相互作用。

We repotr the experimental results concerning the nature of transport noise, and rf-properties in Superconductor-constrictions-Superconductor (S-c-S) quasi-one-dimensional mesoscopic device. These devices were fabricated by applying voltage pulses to an insulating Nb/Insulator/Nb (or NbN) sandwich in liquid helium (4.2K). By this method, we could continuously vary the quasiparticle current-voltage (I-V) curve from insulator to tunnel-contact and finally up to perfectly metallic conducting interface. We found that I,dV/dI vs. V characteristics is colsely with the predicrions of the Blonder, Tinkham and Klapwijk (BTK), and Octabio and BTK (OTBK) theories. We also found that noise voltage power spectral density Sv (f) decreases quickly with increasing device quality factor Q^<-1> and saturates for Q^<-1>>2. This saturation suggests that within the framework of the theoretical model (Hooge model) the defect related number of carriers near the constrictions no longer changes for Q^<-1>>2 regime. In our samples, clear and periodie dV/dI peaks were observed only for clean metallic devices. The origin of these periodic dV/dI peaks above gap voltage may be associated to the quantum size effect, or the geometrical resonance model which takes into account the quantization of the density of states in the constriction. New microwave-induced steps were observed in the current-voltage characteristics of the devices with microwave irradiation. The observed steps are different from the features of the well-known "Shapiro steps". Overall features of such microwave-induced steps can not be explained using existing models. Although the origin of these peaks is not clear yet, one possible origin of this phenomena is the interaction of microwave field with Andreev-reflected electron/hole in the constriction.