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Dissipative processes in superconducting nanodevices: nanowire-resonators, shunted nanowires, and graphene proximity junctions

机译:超导纳米器件中的耗散过程:纳米线谐振器,分流纳米线和石墨烯邻近结

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摘要

The topic of superconducting nanowires has recently been an interesting field of research which has included the study of the superconductor to insulator transition (SIT), the observation of macroscopic quantum behavior such as quantum phase slips (QPS), and the potential use of nanowires as qubits. Superconducting coplanar microwave waveguide resonators have also become a popular way of studying superconducting junctions and qubits, as they provide an extremely low noise environment. For example, superconducting two-dimensional Fabry-Perot resonators have been used by other groups to make non-demolition measurements of a qubit. The motivation of this thesis will be the merging of the fields of superconducting nanowires and the technique of using superconducting microwave resonators to study junctions by incorporating a nanowire into the resonator itself at a current anti-node. By doing this, the nonlinear effects of the nanowire can be studied which may find application in single photon detectors, mixers, and the readout of qubits. We also employ the technique of molecular templating to fabricate some of the thinnest superconducting nanowires ever studied (down to ~ 5 nm in diameter in some cases). In this thesis, we extend the understanding of the nonlinear properties of a nanowire- resonator system and investigate a new type of nonlinearity that involves a pulsing regime between the superconducting and normal phases of the nanowire. We develop a model, which describes the results quantitatively and by modeling the system, we are able to extract information regarding the relaxation time of the nanowire back into the superconducting state. We also study double nanowire-resonator systems where two closely spaced parallel nanowires interrupt the resonator center conductor and form a loop where vortex tunneling processes can occur. Using a double nanowire-resonator we are able to observe the Little-Parks effect at low temperatures (where the resistance of the wires is immeasurably low) and are able to confirm the multivalued nature of the current phase relationship (CPR) in nanowires. Additionally, we observe an anomalous transmission regime where the periodic pulsing is replaced by stochastic amplitude fluctuations. In addition to microwave measurements on nanowires, we also study the normal state in resistively shunted nanowires with dc measurements where the inclusion of a shunt resistor is observed to change the nature of the normal state from the Joule heated state to a state that preserves phase coherence. Finally, the statistics on switching current events in graphene proximity junctions are analyzed and compared to the well known results for Josephson junctions. Only thermal activation (and no macroscopic quantum tunneling) is observed in graphene proximity superconducting junctions down to temperatures of ~ 300 mK.
机译:超导纳米线的主题近来是一个有趣的研究领域,包括超导体到绝缘体过渡(SIT)的研究,宏观量子行为(如量子相滑(QPS))的观察以及纳米线的潜在用途。量子比特。超导共面微波波导谐振器也已成为研究超导结和量子位的一种流行方式,因为它们提供了极低的噪声环境。例如,其他团体已使用超导二维法布里-珀罗谐振器进行量子位的非爆破测量。本文的动机是将超导纳米线领域与通过在当前波腹处将纳米线结合到谐振器本身中而使用超导微波谐振器研究结点的技术相融合。通过这样做,可以研究纳米线的非线性效应,该效应可以在单光子检测器,混合器和量子位的读出中找到应用。我们还采用了分子模板技术来制造一些研究过的最薄的超导纳米线(在某些情况下,直径可降至约5 nm)。在本文中,我们扩展了对纳米线-谐振器系统非线性特性的理解,并研究了一种新型的非线性,其中涉及纳米线的超导相和正常相之间的脉冲状态。我们开发了一个模型,该模型定量地描述了结果,并且通过对系统进行建模,我们能够提取有关纳米线恢复到超导状态的弛豫时间的信息。我们还研究了双纳米线谐振器系统,其中两个紧密间隔的平行纳米线中断了谐振器中心导体并形成了可能发生旋涡隧穿过程的环路。使用双纳米线谐振器,我们能够在低温下观察到Little-Parks效应(在这种情况下,导线的电阻非常低),并且能够确认纳米线中电流相位关系(CPR)的多值性质。此外,我们观察到一种异常的传输方式,其中周期性脉冲被随机振幅波动所代替。除了在纳米线上进行微波测量外,我们还通过直流测量研究电阻分流纳米线上的正常状态,观察到包含分流电阻器将正常状态的性质从焦耳加热状态改变为保持相干的状态。最后,分析了石墨烯邻近结中开关电流事件的统计数据,并将其与约瑟夫森结的众所周知的结果进行了比较。在低至约300 mK的温度下,在石墨烯邻近超导结中仅观察到热激活(并且没有宏观量子隧穿)。

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  • 作者

    Brenner Matthew W.;

  • 作者单位
  • 年度 2011
  • 总页数
  • 原文格式 PDF
  • 正文语种 {"code":"en","name":"English","id":9}
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