Nonlinear Properties of Supercurrent-Carrying Single- and Multi-Layer Thin-Film Superconductors
Nonlinear Properties of Supercurrent-Carrying Single- and Multi-Layer Thin-Film Superconductors
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DOI：
10.1007/s10909-019-02306-3
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发表时间：
2019-07
影响因子：
2
通讯作者：
Songyuan Zhao;S. Withington;D. Goldie;C. N. Thomas
中科院分区：
文献类型：
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作者：
Songyuan Zhao;S. Withington;D. Goldie;C. N. Thomas
超导薄膜是许多量子传感器和量子计算设备的核心：动力学电感探测器（KID），行波参量放大器（TWPA），量子比特和基于自旋的量子存储元件。在所有情况下，由超电流产生的非线性都是行为的关键方面，因为它是设备（TWPA）操作的核心，或者因为它会导致非理想的二阶效应（KID）。在这里，我们提出了一个分析的超导薄膜，是基于广义Usadel方程。我们的分析框架适用于均匀和多层薄膜，并可用于计算所得到的态密度，超导转变温度，超导临界电流，复电导率，复表面阻抗，传输线传播常数，和非线性动力学电感超导电流的存在。我们的分析给出了一个给定的材料组合和几何形状的动力学电感非线性（）的规模，并在优化设计的检测器和放大器的材料，几何形状和尺寸方面是很重要的。为了研究我们的分析在大范围的超导电流的有效性，我们测量了超导薄膜的转变温度作为直流超导电流的函数。这些测量结果与我们在实验相关的电流值范围内的理论预测吻合得很好。
Superconducting thin films are central to the operation of many kinds of quantum sensors and quantum computing devices: kinetic inductance detectors (KIDs), travelling-wave parametric amplifiers (TWPAs), qubits, and spin-based quantum memory elements. In all cases, the nonlinearity resulting from the supercurrent is a critical aspect of behaviour, either because it is central to the operation of the device (TWPA), or because it results in nonideal second-order effects (KID). Here, we present an analysis of supercurrent-carrying superconducting thin films that is based on the generalized Usadel equations. Our analysis framework is suitable for both homogeneous and multi-layer thin films, and can be used to calculate the resulting density of states, superconducting transition temperature, superconducting critical current, complex conductivities, complex surface impedances, transmission line propagation constants, and nonlinear kinetic inductances in the presence of supercurrent. Our analysis gives the scale of kinetic inductance nonlinearity () for a given material combination and geometry, and is important in optimizing the design of detectors and amplifiers in terms of materials, geometries, and dimensions. To investigate the validity of our analysis across a wide range of supercurrent, we have measured the transition temperatures of superconducting thin films as a function of DC supercurrent. These measurements show good agreement with our theoretical predictions in the experimentally relevant range of current values.