Non-bolometric bottleneck in electron-phonon relaxation in ultra-thin WSi film

TL;DR

This paper presents a model of the internal phonon bottleneck in ultrathin WSi films, demonstrating how nonescaping phonons limit electron-phonon relaxation, supported by experimental measurements and simulations.

Contribution

The study introduces a new model distinguishing escaping and nonescaping phonons, providing experimental evidence of the internal phonon bottleneck in ultrathin metal films.

Findings

Electron-phonon relaxation time tau_{e-ph} = 140-190 ps at 3.4 K

Experimental proof of the internal phonon bottleneck

Model and experiment show good agreement

Abstract

We developed the model of the internal phonon bottleneck to describe the energy exchange between the acoustically soft ultrathin metal film and acoustically rigid substrate. Discriminating phonons in the film into two groups, escaping and nonescaping, we show that electrons and nonescaping phonons may form a unified subsystem, which is cooled down only due to interactions with escaping phonons, either due to direct phonon conversion or indirect sequential interaction with an electronic system. Using an amplitude-modulated absorption of the sub-THz radiation technique, we studied electron-phonon relaxation in ultrathin disordered films of tungsten silicide. We found an experimental proof of the internal phonon bottleneck. The experiment and simulation based on the proposed model agree well, resulting in tau_{e-ph} = 140-190 ps at T_C = 3.4 K, supporting the results of earlier measurements by independent techniques.