Quasiparticle lifetimes and tunneltimes in SIS junctions for X-ray spectroscopy

O.J. Luiten (Corresponding Author), H.L. van Lieshout, F.A. Michels, P. Valko, M.P. Bruijn, F. Kiewiet, D.J. Adelerhof, A.W. Hamster, G.C.S. Brons, J. Flokstra

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The quasiparticle lifetimes and tunneltimes in SIS tunnel junctions are essential parameters in the development of these devices for high resolution X-ray spectroscopy. We present a simple analytical model which allows us to calculate both the risetime and the total charge of the integrated tunnel current following an X-ray event. Simultaneous measurement of both the total charge and the risetime thus becomes a useful diagnostic tool for quantitative analysis. We have applied the model to recent X-ray measurements on a Nb/AlOx SIS junction. We find that the energy resolution achieved in this device is mainly limited by variations in the thickness of the counter electrode.


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