Signature of the Reduced Sound Velocity in Thin NbN Films

Signature of the Reduced Sound Velocity in Thin NbN Films

Here, we investigate thermal transport and phonon dynamics in the 30-nm thick NbN device. By measuring the thermal resistance <inline-formula><tex-math notation="LaTeX">Z_{\text{2}D}</tex-math></inline-formula> at temperatures beyond the critical temperature <inl...

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Bibliographic Details
Published in:IEEE transactions on applied superconductivity Vol. 34; no. 3; pp. 1 - 5
Main Authors: Baeva, Elmira, Soldatenkova, Maria, Titova, Nadezhda, Kolbatova, Anna Igorevna, Gol'tsman, Gregory
Format: Journal Article
Language:English
Published: New York IEEE 01-05-2024
The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subjects:
Acoustic velocity
Critical temperature
Electrical resistance measurement
Kapitza resistance
Low temperature
low-temperature detectors
Measuring instruments
Niobium compounds
niobium nitride
phonon heat capacity
phonon mean free path
Phonons
Relaxation time
sound velocity
Substrates
superconducting thin films
Temperature measurement
thermal boundary resistance
Thermal resistance
Thermodynamic properties
Thin films
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Summary:Here, we investigate thermal transport and phonon dynamics in the 30-nm thick NbN device. By measuring the thermal resistance <inline-formula><tex-math notation="LaTeX">Z_{\text{2}D}</tex-math></inline-formula> at temperatures beyond the critical temperature <inline-formula><tex-math notation="LaTeX">T_{c}</tex-math></inline-formula> and the resistance relaxation time <inline-formula><tex-math notation="LaTeX">\tau _{R}</tex-math></inline-formula> in the vicinity of <inline-formula><tex-math notation="LaTeX">T_{c}</tex-math></inline-formula>, we obtain thermal parameters that are consistent with the acoustic mismatch model. Using the acoustic mismatch model and the experimental values of <inline-formula><tex-math notation="LaTeX">Z_{\text{2}D}</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">\tau _{R}</tex-math></inline-formula>, we determine the phonon heat capacity, which also gives access to the sound velocity <inline-formula><tex-math notation="LaTeX">v_{s}</tex-math></inline-formula> in NbN. The obtained value of <inline-formula><tex-math notation="LaTeX">v_{s}</tex-math></inline-formula> is two times lower than the value in bulk NbN, and it corresponds to the velocity estimates obtained by other experimental methods. Our findings can be useful for modeling and improving the performance of low-temperature devices based on NbN films.
ISSN:1051-8223
1558-2515
DOI:10.1109/TASC.2024.3350586