Spin-phonon coupling driven Charge density wave in a Kagome Magnet

TL;DR

This study reveals that spin-phonon coupling drives the formation of a charge density wave in a kagome magnet, with experimental and theoretical evidence showing intertwined spin, charge, and lattice dynamics leading to symmetry breaking.

Contribution

It demonstrates that spin-phonon interactions are fundamental in inducing charge density waves in kagome magnets, combining experimental scattering data with first-principles calculations.

Findings

Observation of charge dimerization superlattice coexisting with CDW

Giant phonon-energy hardening near charge-dimerization wavevectors

Spin excitations intertwine with phonons to drive symmetry breaking

Abstract

The intertwining between spin, charge, and lattice degrees of freedom can give rise to unusual macroscopic quantum states, including high-temperature superconductivity and quantum anomalous Hall effects. Recently, a charge density wave (CDW) is observed in the kagome antiferromagnet FeGe, indicative of possible intertwining physics. An outstanding question is that whether magnetic correlation is fundamental for the spontaneous spatial symmetry breaking orders. Here, utilizing elastic and high-resolution inelastic x-ray scattering, we discover a charge dimerization superlattice that coexists with the 2$\times$2$\times$1 CDW in the kagome sublattice. Most interestingly, between the magnetic and CDW transition temperature, the phonon dynamical structure factor shows a giant phonon-energy hardening and a substantial phonon linewidth broadening near the charge-dimerization wavevectors, both signaling the spin-phonon coupling. By first principles calculations, we show that both the static and dynamic spin excitations intertwine with the phonon to drive the spatial symmetry breaking.