Spatially Resolved Photodoping of Oxygen‐Deficient YBa ₂ Cu ₃ O _7−δ Resonators

Abstract Oxygen‐depleted YBa 2 Cu 3 O 7−δ exhibits a substantial drop in the normal‐state resistivity and an increase in the superconducting critical temperature when illuminated with visible light. The photo‐induced states are metastable, slowly decaying at high temperatures and essentially persistent at low temperatures. In this work, this effect is exploited to modify the response of half‐wavelength YBa 2 Cu 3 O 7−δ resonators and simultaneously the high‐sensitivity of the resonant circuit is used to investigate the persistent photodoping of this material. Under illumination, the bolometric effect and photodoping are clearly distinguished by the different time scales associated with each mechanism. Using a 60 µm‐wide laser spot, the properties of the resonator are locally and reversibly modified, and the position‐dependent sensitivity of the device is demonstrated. This enables the direct imaging of standing waves at both the fundamental resonance and the second harmonic.