Phonon-phonon interactions in the polarizarion dependence of Raman scattering

TL;DR

This paper reveals that the polarization dependence of Raman scattering in organic crystals at finite temperatures requires a fourth-rank tensor formalism, highlighting a new aspect of phonon-phonon interactions beyond phonon lifetime effects.

Contribution

It introduces a fourth-rank tensor approach to describe polarization dependence, accounting for off-diagonal self-energy effects in phonon interactions.

Findings

Polarization dependence described by a fourth-rank tensor.

Off-diagonal self-energy components influence Raman scattering.

New manifestation of phonon-phonon interactions in light scattering.

Abstract

We have found that the polarization dependence of Raman scattering in organic crystals at finite temperatures can only be described by a fourth-rank formalism. This generalization of the second-rank Raman tensor $\mathcal{R}$ stems from the effect of off-diagonal components in the crystal self-energy on the light scattering mechanism. We thus establish a novel manifestation of phonon-phonon interaction in inelastic light scattering, markedly separate from the better-known phonon lifetime.