Modification of electron-phonon coupling by micromachining and suspension

TL;DR

This study investigates how micromachining and suspension of thin gold films alter electron-phonon heat flow at millikelvin temperatures, revealing a change in the power law exponent due to phonon spectrum modification.

Contribution

It provides experimental evidence that micromachining modifies the electron-phonon coupling and phonon spectrum in thin metal films at very low temperatures.

Findings

Power law exponent changed from 5.1 to 4.6 after micromachining.

Modified phonon spectrum explains the change in heat flow behavior.

Results align with theoretical models and previous experiments.

Abstract

Weak electron-phonon interaction in metals at low temperatures forms the basis of operation for cryogenic hot-electron bolometers and calorimeters. Standard power laws, describing the heat flow in the majority of experiments, have been identified and derived theoretically. However, a full picture encompassing experimentally relevant effects such as reduced dimensionality, material interfaces, and disorder is in its infancy, and has not been tested extensively. Here, we study the electron-phonon heat flow in a thin gold film on a SiO${}_2$ platform below 100 mK using supercurrent thermometry. We find the power law exponent to be modified from 5.1 to 4.6 as the platform is micromachined and released from its substrate. We attribute this change to a modified phonon spectrum. The findings are compared to past experiments and theoretical models.