Optical response of an interacting polaron gas in strongly polar crystals

TL;DR

This paper models the optical conductivity of an interacting polaron gas in strongly polar crystals, revealing that phonon-electron interactions explain experimental spectra without extra mechanisms.

Contribution

It introduces an extended random phase approximation accounting for phonon-electron mixing, providing new insights into optical responses in high dielectric constant materials.

Findings

Phonon-electron mixing significantly affects optical spectra.

Dynamic screening explains experimental features in SrTiO3.

No additional mechanisms needed for observed spectra.

Abstract

Optical conductivity of an interacting polaron gas is calculated within an extended random phase approximation which takes into account mixing of collective excitations of the electron gas with LO phonons. This mixing is important for the optical response of strongly polar crystals where the static dielectric constant is rather high: strontium titanate is the case. The present calculation sheds light on unexplained features of experimentally observed optical conductivity spectra in $n$-doped SrTiO$_{3}$. These features appear to be due to dynamic screening of the electron-electron interaction by polar optical phonons and hence do not require additional mechanisms for the explanation.