Phonon Magnetochiral Effect

TL;DR

This paper demonstrates the phonon magnetochiral effect in a chiral ferrimagnet, showing nonreciprocal sound velocity influenced by magnetic field and crystal chirality, explained by magnon-phonon hybridization.

Contribution

First experimental observation of phonon magnetochiral effect in a chiral-lattice ferrimagnet with detailed analysis of its mechanisms.

Findings

Sound velocity differs for opposite propagation directions.

Nonreciprocity depends on crystal chirality.

Effect is enhanced below magnetic ordering temperature.

Abstract

Magnetochiral effect (MChE) of phonons, a nonreciprocal acoustic property arising due to the symmetry principles, is demonstrated in a chiral-lattice ferrimagnet Cu$_2$OSeO$_3$. Our high-resolution ultrasound experiments reveal that the sound velocity differs for parallel and antiparallel propagation with respect to the external magnetic field.The sign of the nonreciprocity depends on the chirality of the crystal in accordance with the selection rule of the MChE. The nonreciprocity is enhanced below the magnetic ordering temperature and at higher ultrasound frequencies, which is quantitatively explained by a proposed magnon-phonon hybridization mechanism.