Effective phonon models based on symmetry-adapted multipole basis -- Hidden chiral phonon angular momentum splitting in ferroaxial systems

TL;DR

This paper introduces a symmetry-based method for modeling phonons using multipole bases, revealing hidden chiral phonon phenomena in ferroaxial systems and offering ways to manipulate phonon properties.

Contribution

It develops a unified symmetry framework for understanding hidden and emergent phonon phenomena based on multipole decomposition.

Findings

Ferroaxial order induces hidden sublattice-resolved chiral phonons.

Additional polar contributions lead to finite global phonon chirality.

The framework links electronic orderings and external fields to phonon control.

Abstract

We propose a symmetry-based framework for constructing effective harmonic phonon models using a symmetry-adapted multipole basis. By decomposing the force-constant matrix into bond-centered electric multipoles, we identify the minimal microscopic ingredients responsible for phonon angular-momentum splitting. Applying this framework to a minimal zigzag-chain model, we show that ferroaxial order gives rise to a hidden sublattice-resolved chiral phonons, while an additional polar contribution leads to finite global chirality. Our results provide a unified symmetry-based description of hidden and emergent phonon phenomena and suggest a route to control phonon properties via electronic orderings and external fields.