Selective observation of enantiomeric chiral phonons in $\alpha$-quartz

TL;DR

This study uncovers chiral phonons in $ ext{α}$-quartz through circularly polarized Raman spectra, revealing their angular momentum properties, selection rules, and enantiomer-specific helicity, advancing understanding of phonon chirality.

Contribution

It provides the first experimental observation and analysis of chiral phonons in quartz, including their selection rules and enantiomer-dependent helicity.

Findings

Chiral phonons exhibit opposite angular momenta in enantiomers.

Raman selection rules for chiral phonons are established.

Helicity of phonons depends on quartz enantiomer.

Abstract

We report anomalous circularly polarized Raman spectra of phonons in right- and left-handed quartzes. The phonon branches splitting from the E-mode at a finite wavenumber were found to be chiral with mutually opposite angular momenta. Our analysis reveals the Raman selection rules for chiral phonons. We also find that the conservation of angular momentum should be satisfied between two photons and one chiral phonon in the Raman process. Furthermore, we experimentally proved that the helicity of phonons with a certain frequency and wavevector should be opposite in the other enantiomer.