Transient response of quasiparticle injected superconducting links

We have fabricated submicron injection-controlled NbN links with gain and measured their injection-triggered superconducting-to-normal transition to occur in 0.5-2.6 ns at 4 K, governed by condensate dynamics. The transient pulse shape displays a rising-edge kinetic-inductance spike and a strong dependence on the amplitude of the injected quasiparticle current similar to microbridges driven by supercritical currents. A modified dynamic effective-temperature model is used to interpret the transient time and the pulse shape.