Magnetic order induced chiral phonons in a ferromagnetic Weyl semimetal

TL;DR

This study discovers chiral phonon modes in a ferromagnetic Weyl semimetal, induced by magnetic order, and demonstrates their controllability via magnetic fields, opening new avenues for manipulating chiral quasiparticles.

Contribution

It reveals magnetic order as a new mechanism for inducing chiral phonons in a centrosymmetric Weyl semimetal, demonstrated through helicity-resolved magneto-Raman spectroscopy.

Findings

Spontaneous splitting of in-plane Eg phonon modes into chiral modes below Curie temperature

Hysteresis in phonon splitting correlates with magnetization

Chiral phonon splitting reaches 1.27 cm-1 at low temperatures

Abstract

Chiral phonons are vibrational modes in a crystal that possess a well-defined handedness or chirality, typically found in materials that lack inversion symmetry. Here we report the discovery of chiral phonon modes in the kagome ferromagnetic Weyl semimetal Co3Sn2S2, a material that preserves inversion symmetry but breaks time-reversal symmetry. Using helicity-resolved magneto-Raman spectroscopy, we observe the spontaneous splitting of the doubly degenerate in-plane Eg modes into two distinct chiral phonon modes of opposite helicity when the sample is zero-field cooled below the Curie temperature, in the absence of an external magnetic field. As we sweep the out-of-plane magnetic field, this Eg phonon splitting exhibits a well-defined hysteresis loop directly correlated with the material's magnetization. The observed spontaneous splitting reaches up to 1.27 cm-1 at low temperatures, progressively diminishes with increasing temperature, and completely vanishes near the Curie temperature. Our findings highlight the role of the magnetic order in inducing chiral phonons, paving the way for novel methods to manipulate chiral phonons through magnetization and vice versa. Additionally, our work introduces new possibilities for controlling chiral Weyl fermions using chiral phonons.