Theory of Out-of-Equilibrium Ultrafast Relaxation Dynamics in Metals

TL;DR

This paper develops a first-principles out-of-equilibrium theory to accurately describe ultrafast relaxation dynamics in metals, capturing electronic and phononic energy transfer beyond the two-temperature model.

Contribution

It introduces a microscopic, parameter-free model that accounts for all key energy transfer processes during ultrafast relaxation in metals.

Findings

Detailed relaxation in FePt is out-of-equilibrium for picoseconds

Model accurately captures electron-phonon and phonon-phonon interactions

Provides a comprehensive description of energy transfer dynamics

Abstract

Ultrafast laser excitation of a metal causes correlated, highly nonequilibrium dynamics of electronic and ionic degrees of freedom, which are however only poorly captured by the widely-used two-temperature model. Here we develop an out-of-equilibrium theory that captures the full dynamic evolution of the electronic and phononic populations and provides a microscopic description of the transfer of energy delivered optically into electrons to the lattice. All essential nonequilibrium energy processes, such as electron-phonon and phonon-phonon interactions are taken into account. Moreover, as all required quantities are obtained from first-principles calculations, the model gives an exact description of the relaxation dynamics without the need for fitted parameters. We apply the model to FePt and show that the detailed relaxation is out-of-equilibrium for picoseconds.