Energy Dissipation during Diffusion at Metal Surfaces: Disentangling the Role of Phonons vs. Electron-Hole Pairs

TL;DR

This study combines experiments and simulations to quantify how phonons and electron-hole pairs contribute to energy loss during Na atom diffusion on Cu(111), revealing a notable electronic component despite minimal electronic friction.

Contribution

It provides a detailed separation of phononic and electronic energy dissipation mechanisms during atomic diffusion on metal surfaces using advanced experimental and computational methods.

Findings

Approximately 20% of energy loss is due to electronic friction.

Electronic non-adiabaticity plays a significant role in thermalization.

Phononic dissipation is dominant but not exclusive.

Abstract

Helium spin echo experiments combined with ab initio-based Langevin molecular dynamics simulations are used to quantify the adsorbate-substrate coupling during the thermal diffusion of Na atoms on Cu(111). An analysis of trajectories within the local density friction approximation allows the contribution from electron-hole pair excitations to be separated from the total energy dissipation. Despite the minimal electronic friction coefficient of Na and the relatively small mass mismatch to Cu promoting efficient phononic dissipation, about $(20\pm5)\%$ of the total energy loss is attributable to electronic friction. The results suggest a significant role of electronic non-adiabaticity in the rapid thermalization generally relied upon in adiabatic diffusion theories.