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

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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.