Quasiparticle generation efficiency in superconducting thin films

Thin-film superconductors with thickness 30-500 nm are used as non-equilibrium quantum detectors for photons, phonons or more exotic particles. One of the most basic questions in determining their limiting sensitivity is the efficiency with which the quanta of interest couple to the detected quasipa...

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Bibliographic Details
Published in:Superconductor science & technology 2014-05, Vol.27 (5), p.55012-6
Main Authors: Guruswamy, T, Goldie, D J, Withington, S
Format: Article
Language:English
Subjects:
Computing time
Constraining
Detectors
kinetic inductance detectors
Mathematical models
noise equivalent power
non-equilibrium superconductivity
Photons
Superconductivity
Superconductors
Thin films
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Summary:Thin-film superconductors with thickness 30-500 nm are used as non-equilibrium quantum detectors for photons, phonons or more exotic particles. One of the most basic questions in determining their limiting sensitivity is the efficiency with which the quanta of interest couple to the detected quasiparticles. As low temperature superconducting resonators, thin films are attractive candidates for producing quantum-sensitive arrayable sensors and the readout uses an additional microwave probe. We have calculated the quasiparticle generation efficiency ηs for low energy photons in a representative, clean thin-film superconductor (Al) operating well below its superconducting transition temperature as a function of film thickness, within the framework of the coupled kinetic equations described by Chang and Scalapino (1978 J. Low Temp. Phys. 31 1-32). We have also included the effect of a lower frequency probe. We show that phonon loss from the thin film reduces ηs by as much as 40% compared to earlier models that considered relatively thick films or infinite volumes. We also show that the presence of the probe and signal enhances the generation efficiency slightly. We conclude that the ultimate limiting noise equivalent power of this class of detector is determined by the thin-film geometry.
ISSN:0953-2048
1361-6668
DOI:10.1088/0953-2048/27/5/055012