Impurity effects on optical response in a finite band electronic system coupled to phonons

TL;DR

This paper investigates how impurities and phonons influence the optical response in finite band electronic systems, revealing that traditional infinite band assumptions do not hold and that impurity effects significantly alter optical properties.

Contribution

It introduces a new understanding of impurity and phonon effects on optical responses in finite band systems, challenging traditional infinite band models.

Findings

Impurity and phonon contributions to scattering are not additive.

Optical mass renormalization can change sign with frequency.

Optical scattering rate is reduced and does not reach its high-frequency quasiparticle value.

Abstract

The concepts, which have traditionally been useful in understanding the effects of the electron--phonon interaction in optical spectroscopy, are based on insights obtained within the infinite electronic band approximation and no longer apply in finite band metals. Impurity and phonon contributions to electron scattering are not additive and the apparent strength of the coupling to the phonon degrees of freedom is substantially reduced with increased elastic scattering. The optical mass renormalization changes sign with increasing frequency and the optical scattering rate never reaches its high frequency quasiparticle value which itself is also reduced below its infinite band value.