Bias dependance of the response of superconducting tunnel junctions used as photon detectors

In the last decade, several research groups have developed superconducting tunnel junctions (STJ) for photon detection in astronomy. Despite extensive studies, the behavior of multi-layered devices, subject to the superconducting proximity effect (proximized devices), has remained difficult to model. Recently, a new model has been presented, leading to a more realistic approach for the photon detection within an STJ. This model is based on the existence of local traps in the superconducting electrodes of the STJ. In this paper, we show that the new model is successful in predicting the bias dependence of the response of an STJ. The bias dependence also demonstrates that the quasiparticles, i.e. the charge carriers created as a result of the photon absorption process, cannot relax down to the superconducting energy gap. This result is important, since most theoretical developments to date (implicitly) assume that quasiparticle relax to the gap energy.