Screening effects in the electron-optical phonon interaction

TL;DR

This paper clarifies how screening effects influence the renormalization of optical phonons by electron-phonon interactions, showing that proper screening leads to phonon softening and complex mode behavior in different dimensions.

Contribution

It demonstrates the importance of screening effects in electron-optical phonon interactions and explains the resulting phonon spectrum modifications across dimensions.

Findings

Screening causes optical phonon softening in 3D.

Static screening for short-wavelength phonons; dynamic for long-wavelength.

Phonon-plasmon mode splitting in 1D and 2D systems.

Abstract

We show that recently reported unusual hardening of optical phonons renormalized by the electron-phonon interaction is due to the neglect of screening effects. When the electron-ion interaction is properly screened optical phonons soften in three dimension. It is important that for short-wavelength optical phonons screening is static while for long-wavelength optical phonons screening is dynamic. In two-dimensional and one-dimensional cases due to crossing of the nonperturbed optical mode with gapless plasmons the spectrum of renormalized optical phonon-plasmon mode shows split momentum dependence.