The interpretation of the power dependence of the unloaded quality factor of superconductive microstrip resonators

For microstrip resonators fabricated from YBa2Cu3O7-δ (YBCO) thin film on LaAlO3 (001) substrates, this paper reports the experimental observation and theoretical explanation of the power dependence of the unloaded quality factor (Q0). Two kinds of Q0 behaviour were observed. In one case, with the increase of input power, Q0 dropped at first rather quickly, then slowly and then again drastically. In the other case, Q0 remained almost unchanged but, beyond a certain input power level, dropped very rapidly. To interpret these behaviours, two phenomenological expressions for local surface resistance (Rs) were proposed. According to these expressions Rs is a function of the surface rf current density (Js) in the strip which is strongly non-uniform spatially. By choosing proper values for the fitting parameters in these Rs expressions, the dependence of Q0 on the input power was computed, resulting in good agreement between the theoretical calculations and the experimental measurements. (author)