Antiferro-Chiral Phonons as Conjugate Fields to Néel Order in $\mathcal{P}\mathcal{T}$-Symmetric Antiferromagnets

Abstract

Chiral phonons act as a phononic conjugate field to net magnetization, enabling phononic detection and control of ferromagnetic order. Whether an analogous phononic coupling exists for the compensated Néel order of antiferromagnets has remained open. Here we show that, in $\mathcal{P}\mathcal{T}$-symmetric antiferromagnets, phonons with sublattice-staggered angular momentum can couple to the Néel vector like a conjugate field. Such coupling can be induced by the molecular Berry curvature-induced gyroscopic coupling between Raman and infrared-active phonons. The gyroscopic coupling is odd under both $\mathcal{P}$ and $\mathcal{T}$ while preserving their product. $\mathcal{P}\mathcal{T}$ symmetry forbids the resulting normal modes to have a net phonon angular momentum (PAM) while allows counter-rotating local motion on inversion-related sublattices, which are dubbed the antiferro-chiral phonons (AFCPs). Reversing the Néel vector reverses the staggered phonon chirality and the sign of the coupling. Our results indicate AFCPs can serve as probes and control knobs of Néel order.

arXiv comment10 pages, 4 figures, 1 table, Supplemental Material added as Ancillary file, new end matter section is added