Fast nonequilibrium induction detectors based on thin superconducting films

A new type of fast detector is proposed. The operation of the detector is based on the change induced in the kinetic inductance of NbN and YBa₂Cu₃O_7−δ superconducting films by nonequilibrium quasiparticles produced by electromagnetic radiation. The speed of a NbN detector is essentially temperature-independent and is less than 1 ps. A model based on the Omen-Scalapino scheme describes well the experimental dependence of the voltage-power sensitivity of a NbN detector on the modulation frequency of the radiation. A low equilibrium quasiparticle density and a high quantum yield give detecting power D*=10¹²W⁻¹ · cm · Hz^1/2 at temperature T=4.2 K and D*=10¹⁶ W⁻¹ · cm · Hz^1/2 at temperature T=1.6 K. The time constant of the low-temperature YBaCuO induction detector is determined only by the electron-phonon interaction time τ _e-ph ^d in the nodal regions. Zh. Tekh. Fiz. 68, 63–69 (October 1998)