Charge Multiplication Factor in STJ Detectors
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This work pays attention to the inconsistency of the commonly used formulae for the internal gain, and the multitunneling noise factor in superconducting tunnel junction (STJ) detectors with experimental data. The origin of this inconsistency is in the fact that these formulae give the mean value and the relative variance of the number of crossings of the insulating barrier by a quasiparticle, but not the net charge transferred through the barrier that actually determines the signal of an STJ detector. In this work, the theory of branching cascade processes was applied to the process of multiple tunneling in STJ. The duality nature of quasiparticles and the coupling of the quasiparticle and phonon subsystems were taken into account. The general formulae for time dependences of the moments of the charge multiplication factor were derived.
KeywordsSuperconducting tunnel junction Energy resolution Quasiparticle tunneling
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