Nonequilibrium Electron Dynamics In Pump-Probe Spectroscopy: Role Of Excited Phonon Populations

TL;DR

This paper investigates how excited phonon populations influence the relaxation rates of nonequilibrium electrons in pump-probe spectroscopy, revealing that phonon excitation suppresses electron decay and affects spectral properties.

Contribution

It introduces a self-consistent nonequilibrium Green's function approach to account for transient phononic modifications in electron relaxation dynamics.

Findings

Excited phonon populations suppress electron decay rates.

Time-dependent decay rates observed experimentally.

Enhanced phonon absorption alters spectral functions.

Abstract

We study the role of excited phonon populations in the relaxation rates of nonequilibrium electrons using a nonequilibrium Green's function formalism. The transient modifications in the phononic properties are accounted for by self-consistently solving the Dyson equation for the electron and phonon Green's functions. The pump induced changes manifest in both the electronic and phononic spectral functions. We find that the excited phonon populations suppress the decay rates of nonequilibrium electrons due to enhanced phonon absorption. The increased phonon occupation also sets the nonequilibrium decay rates and the equilibrium scattering rates apart. The decay rates are found to be time-dependent, and this is illustrated in the experimentally observed population decay of photoexcited $\mathrm{Bi}_{1.5}\mathrm{Sb}_{0.5} \mathrm{Te}_{1.7}\mathrm{Se}_{1.3}$.