Characterization of YBa₂Cu₃O_7−δ coplanar resonator for microwave kinetic inductance detectors

We demonstrate an improved YBa₂Cu₃O_7−δ -based microwave kinetic inductance detector with a quality factor Q i ∼ 2.5 × 10 4 and noise equivalent power, ∼ 10 − 12 W Hz − 1 at 10 K. Zero field cooled (ZFC) and field cooled (FC) measurements of the magnetic field dependence of the resonance characteristics, show substantially different behavior, indicating that both the screening currents and vortices play a role. The ZFC measurements exhibit a sharp decrease of the resonance frequency, f r , and Q i at low fields, up to the full penetration field, revealing the dominant role of the screening currents. In contrast, the FC measurements exhibit a moderate decrease of f r and Q i with field, revealing the role of vortices and reflecting the field dependence of the penetration depth in a d-wave superconductor.