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Regular version of the site

Article

Thermal properties of NbN single-photon detectors

Physical Review Applied. 2018. Vol. 10. P. 064063-1-064063-8.
Baeva E., Sidorova M. V., Korneev A., Smirnov K., Divochy A., Morozov P., Золотов Ф. И., Vakhtomin Y. B., Semenov A. V., Klapwijk T. M., Khrapai V.S., Goltsman G.

We investigate thermal properties of a NbN single-photon detector capable of unit internal detec-
tion efficiency. Using an independent calibration of the coupling losses we determine the absolute
optical power absorbed by the NbN film and, via a resistive superconductor thermometry, the ther-
mal resistance Z(T) of the NbN film in dependence of temperature. In principle, this approach
permits a simultaneous measurement of the electron-phonon and phonon-escape contributions to
the energy relaxation, which in our case is ambiguous for their similar temperature dependencies.
We analyze the Z(T) within the two-temperature model and impose an upper bound on the ratio
of electron and phonon heat capacities in NbN, which is surprisingly close to a recent theoretical
lower bound for the same quantity in similar devices.