Ultrafast YBCO photodetector based on the kinetic-inductive process

We make use of the nonequilibrium kinetic-inductive effect in epitaxial YBa₂Cu₃O_7-x (YBCO) thin films to demonstrate an ultrafast, high-sensitivity, broadband photodetector. The photoresponse of a 5-μm-wide, 10-μm-long, 100-nm-thick YBCO microbridge embedded in a 20-μm-wide coplanar strip transmission line was measured using a >1-THz, submillivolt-sensitivity electro-optic sampling system. We performed a comprehensive study of the optical power and wavelength dependency on the YBCO photodetector response. The quantum coherence Rothwarf-Taylor model together with the hot-electron relaxation effect were used to explain the measured data and to extract the number of generated quasiparticles for each absorbed photon, revealing the intrinsic quantum yield of our device to be ~450. The amplitude, response time, and the intrinsic gain of the YBCO photoresponses were observed to be spectrally flat over the tested range of 390 nm to 810 nm