Importance of coupling strength in shaping electron energy loss and phonon spectra of phonon-plasmon systems

TL;DR

This paper systematically analyzes phonon-plasmon coupled excitations in 3D polar systems, highlighting how electron-phonon interaction strength influences spectral weights, dispersion, and damping, with implications for experimental spectral estimation.

Contribution

It provides a comprehensive spectral analysis of phonon-plasmon excitations across parameter space, emphasizing the role of coupling strength and adiabaticity in spectral features.

Findings

EPI strength significantly affects spectral weight distribution.

Strong couplings lead to large phonon production contributions.

Spectral behaviors are accurately modeled across the parameter space.

Abstract

A systematic analysis of phonon-plasmon coupled excitations in three-dimensional (3D) polar systems is provided through the prism of both raw and integrated electron energy loss spectroscopy (EELS) and phonon spectra in the whole relevant parametric space, spanned by the adiabaticity parameter and the electron-phonon interaction (EPI) strength. We show that the EPI strength plays a prominent role in distributing spectral weights among excitations, providing an experimentally convenient way to estimate it from integrated spectra. By projecting the excitations onto the phonon degree of freedom, we also report for strong couplings large phonon production contributions, which are of very different origins depending on the adiabaticity parameter. In parallel to this thorough spectral weights analysis, excitations' dispersion evolutions, dampings, and various limiting behaviors are qualitatively and quantitatively correctly accounted for in the whole parametric space.