Observation of fast nonbolometric optical response of nongranular high T c Y1Ba2Cu3O7−x superconducting thin films

We report fast optical response measurements in predominantly c-axis oriented crystalline Y1Ba2Cu3O7−x superconducting thin films at the wavelength of 1.06 μm. We identify two distinct components contributing to the optical response: a nonbolometric (as fast as 1 ns) and a bolometric component (several ns). The bolometric component is stronger at temperatures in the vicinity of the transition region to the normal state. The nonbolometric component is dominant at temperatures below the transition region showing weak temperature dependence and a linear dependence on the bias current. This nonbolometric component may be evidence for nonequilibrium effects (e.g., breaking of Cooper pairs and generation of quasiparticles or other mechanisms). These results suggest that with proper optimization of device parameters (its geometry, critical current density, etc.) high-speed detectors with reasonable sensitivity covering a broad electromagnetic spectrum (visible and infrared) may be developed.