Phonon line shape in disordered A3C60 (A= K, Rb)

TL;DR

This paper models the phonon line shape in disordered A3C60, showing how orientational disorder affects Raman scattering and provides insights into electron-phonon interactions and molecular orientation correlations.

Contribution

It introduces a calculation of phonon self-energy considering orientational disorder, linking Raman scattering line shapes to electron-phonon coupling and molecular orientation correlations.

Findings

Disorder causes violation of momentum conservation in Raman scattering.

Line shapes can estimate electron-phonon coupling strength.

Supports local correlation of molecular orientations with 90-degree differences.

Abstract

We present a calculation of the Hg phonon self-energy for a model of A3C60 (A= K, Rb). The orientational disorder of the C60 molecules is included, and the lowest order self-energy diagram is considered. The calculations illustrate that due to the violation of momentum conservation by the orientational disorder, Raman scattering can measure the decay of a phonon in an electron-hole pair, allowing the estimate of the electron-phonon coupling from such experiments. Comparison with experimental line shapes further provides support for a local correlation of the molecular orientations, with neighboring molecules preferentially having orientations differing by a 90 degree rotation.