Anomalous microwave response of high-temperature superconducting thin-film microstrip resonator in weak dc magnetic fields

Abstract

We have studied an anomalous microwave (mw) response of superconducting YBa2Cu3O7-δ (YBCO) microstrip resonators in the presence of a weak dc magnetic field, Hdc. The surface resistance (Rs) and reactance (Xs) show a correlated non-monotonic behavior as a function of Hdc. Rs and Xs were found to initially decrease with elevated Hdc and then increase after Hdc reaches a crossover field, Hc, which is independent of the amplitude and frequency of the input mw signal within the measurements. The frequency dependence of Rs is almost linear at fixed Hdc with different magnitudes (Hc). The impedance plane analysis demonstrates that rH, which is defined as the ratio of the change in Rs(Hdc) and that in Xs(Hdc), is about 0.6 at HdcHc. The Hdc dependence of the surface impedance is qualitatively independent of the orientation of Hdc.