At low temperatures, the thermal wavelength of acoustic phonons in a metallic thin film on a substrate can widely exceed the film thickness. It is thus generally believed that a mesoscopic device operating at low temperature does not carry an individual phonon population. In this work, we provide direct experimental evidence for the thermal decoupling of phonons in a mesoscopic quantum device from its substrate phonon heat bath at a sub-Kelvin temperature. A simple heat balance model assuming an independent phonon bath following the usual electron-phonon and Kapitza coupling laws can account for all experimental observations.
@article{arxiv.1301.3612,
title = {Existence of an Independent Phonon Bath in a Quantum Device},
author = {Laetitia Pascal and Aurelien Fay and Clemens Winkelmann and Hervé Courtois},
journal= {arXiv preprint arXiv:1301.3612},
year = {2015}
}