Anomalous frequency scaling of acoustic phonon damping in nickel cavities fabricated by ps-laser delamination

TL;DR

This study investigates the unusual damping behavior of acoustic phonons in nickel cavities created by ps-laser delamination, revealing frequency-dependent damping that deviates from conventional phonon-phonon scattering models.

Contribution

It demonstrates the anomalous frequency scaling of phonon damping in laser-fabricated nickel cavities and links it to structural modifications caused by the delamination process.

Findings

Low-frequency acoustic waves are long-lived in the cavities.

High-frequency modes >60GHz damp faster than expected.

Structural modifications influence phonon damping behavior.

Abstract

Single-shot picosecond (ps) laser induced delamination allows for the direct generation of suspended membranes from a continuous metallic film, offering a promising platform for control of ultrafast magnetization dynamics driven by acoustic waves. Using the picosecond-ultrasonics method, we demonstrate that long-lived low-frequency acoustic waves can be optically-excited in the delaminated cavities. At the same time, higher-frequency modes >60GHz exhibit a surprisingly fast damping, following a scaling law incompatible with the expected attenuation mediated by phonon-phonon scattering. Comparing measurements between delaminated cavities and a benchmark nickel film in contact with the substrate, we link our findings with structural modifications of the nickel crystal induced by the delamination process.