Investigation on Properties of Kinetic Inductance of High T_c Superconducting Thin Films and its Device Application

本项目研究了高温超导薄膜的动态电感特性，并探讨了利用动态电感作为光探测器的可能性。采用离轴磁控溅射法制备了厚度小于磁穿透深度的高质量YBaCuO薄膜，并利用LC谐振电路测量了薄膜的动态电感。实验上阐明了动力学电感随温度、薄膜质量和薄膜几何形状的变化规律，并将观测特性与理论结果进行了比较。首先，它表明，动态电感的温度依赖性与BCS理论很好地解释。接下来，观察到的动力学值被证明是一致的理论预测从临界温度和薄膜的电阻率。最后，通过考虑薄膜中的电流分布，定量地解释了动态电感对薄膜几何形状的依赖关系，并利用Ginzburg-Landau（GL）理论从理论上阐明了动态电感的非线性特性。结果表明，动态电感可以调制偏置电流和磁场。这一结果意味着动态电感可以用作参数电感。这些理论预测得到了实验证实。在此基础上，我们对高温超导薄膜的动态电感进行了模拟，并讨论了改善动态电感性能的方法。

In this project, we have studied properties of kinetic inductance of high Tc superconducting thin films, and discuss possibility of optical detector using kinetic inductance. High quality YBaCuO thin films, whose thickness is smaller than magnetic penetration depth, are prepared using off-axis magnetron sputtering method, and kinetic inductance of the film is measured with LC-resonant circuit. Dependencies of kinetic inductance of temperature, film quality and film geometry are clarified experimentally, and observed properties are compared with theoretical results. First, it is shown that temperature dependence of kinetic inductance is explained well with BCS theory. Next, observed values of kinetic are shown to be consistent with theoretical ones predicted from critical temperature and resistivity of films. Finally, it is shown that dependence of kinetic inductance on film geometry can be explained quantitatively by taking into account current distribution in the film.Nonlinear properties of kinetic inductance are also clarified theoretically using Ginzburg-Landau (GL) theory. It is shown that kinetic inductance can be modulated with bias current and magnetic field. This result means that kinetic inductance can be used as parametric inductance. These theoretical predictions are confirmed experimentally. From these results, we have made modeling of kinetic inductance of high Tc superconducting thin films, and discussed method for improving properties of kinetic inductance for use of optical detector.