Optical response of YBCO thin films and weak-links

The authors have fabricated films of the high-temperature superconductor YBCO and measured their response to optical and infrared radiation. The response is manifested by a change in the current-voltage characteristics of YBCO weak links. The change is found to be dependent on film quality, operating point, light chopping frequency, and temperature. Depending on the type of anneal, the superconducting films exhibit metallic or semiconducting resistivity behavior above T _c. The optical responsivity of semiconducting films is larger than that of metallic films. By further annealing, semiconducting films could be converted into metallic films with a concurrent decrease in their optical responsivity. Some of the measurements have been performed with the films immersed in superfluid helium to allow the separation of nonequilibrium effects from the equilibrium bolometric response. The results of this preliminary study indicate that patterned YBCO films in the superconducting state can be used as sensitive detectors of light