Quasiparticle diffusion and the energy resolution of superconducting tunneling junctions as photon detectors. II. Experiment

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Abstract
In a previous paper we presented an analytical iterative model to describe the spectral characteristics of a superconducting tunnel junction (STJ) used as a photon detector, in terms of the spatial and temporal evolution of the quasiparticle population in both electrodes. This model includes effects from quasiparticle recombination, multiple quasiparticle tunneling, phonon coupling between the electrodes, asymmetry between base and counter electrode, losses at nonideal edges and diffusive losses into electrical connections, bridges, or localized traps. Here we discuss two examples in which this model is applied to comprehensive experimental datasets obtained with multiple STJ’s, and demonstrate how this model can be used to obtain a better understanding of the factors that limit the energy resolution in STJ’s as photon detectors.