Detection of phonon helicity in nonchiral crystals with Raman scattering

TL;DR

This paper proposes a theoretical method to detect phonon helicity in nonchiral crystals using Raman scattering, revealing how phonon angular momentum influences Raman intensity under wave vector reversal.

Contribution

It introduces a novel theoretical approach to identify phonon helicity signatures in nonchiral materials via Raman scattering analysis.

Findings

Raman intensity varies with phonon wave vector reversal in BaMnSb2

Phonon helicity can be inferred from Raman scattering data

Comparison with chiral crystals highlights unique signatures

Abstract

Recently, it has been predicted that the Berry curvature of electrons can produce an angular momentum for phonons. In systems with time-reversal symmetry, the direction of the phonon angular momentum is locked to the phonon wave vector. Accordingly, this phenomenon has received the name of ``phonon helicity". Here, we present a theory to unveil the signatures of such phonon helicity using Raman scattering. We show that the intensity of Raman scattering for circularly polarized light in BaMnSb$_2$ (a prototypical nonchiral Dirac insulator) changes under a reversal of the phonon wave vector, and that the phonon helicity can be inferred from that change. We compare our results to recent reports of Raman-based detection of phonon angular momentum in chiral crystals.