Energy relaxation and electron-phonon coupling in laser-excited metals

TL;DR

This study uses first principles calculations to analyze how energy transfers between electrons and phonons in laser-excited metals like Aluminium and Copper at very high electron temperatures, revealing mode-specific coupling behaviors.

Contribution

It introduces a detailed first-principles approach to evaluate electron-phonon coupling at high electron temperatures, considering mode-specific effects and temperature dependence.

Findings

Longitudinal acoustic mode dominates electron-phonon coupling in Aluminium across all temperatures.

In Copper, the longitudinal acoustic mode dominates only above 40000 K.

The results align with existing data at room temperature and highlight the limits of zero-temperature approximations at high temperatures.

Abstract

The rate of energy transfer between electrons and phonons is investigated by a first principles framework for electron temperatures up to $T_e=50000$ K while considering the lattice at ground state. Two typical but differently complex metals are investigated, namely Aluminium and Copper. In order to reasonably take the electronic excitation effect into account, we adopt finite temperature density functional theory and linear response to determine the electron-temperature-dependent Eliashberg function and electron density of states. Of the three branch-dependent electron-phonon coupling strengths, the longitudinal acoustic mode plays a dominant role in the electron-phonon coupling for Aluminium for all temperatures considered here, but for Copper it only dominates above an electron temperature of $T_e=40000$ K. The second moment of the Eliashberg function and the electron phonon coupling constant at room temperature $T_e=315$ K show good agreement with other results. For increasing electron temperatures, we show the limits of the $T=0$ approximation for the Eliashberg function. Our present work provides a rich perspective on the phonon dynamics and this will help to improve insight into the underlying mechanism of energy flow in ultra-fast laser-metal interaction.