Electromagnons in the spin collinear state of a triangular lattice antiferromagnet

TL;DR

This study uses terahertz spectroscopy to reveal electromagnon excitations in a triangular lattice antiferromagnet, showing their dependence on magnetic phase and indicating a spin-orbit coupling mechanism.

Contribution

It provides direct spectroscopic evidence of electromagnons in a collinear magnetic phase, highlighting a spin-orbit coupling origin distinct from exchange-striction.

Findings

Electromagnon at 2.3 meV observed in collinear phase

Electromagnon disappears in ferroelectric helimagnetic phase

Spin-orbit coupling mediates the electromagnon

Abstract

Terahertz time-domain spectroscopy was performed to directly probe the low-energy (1-5 meV) electrodynamics of triangular lattice antiferromagnets CuFe1-xGaxO2 (x = 0.00, 0.01, and 0.035). We discovered an electromagnon (electric-field-active magnon) excitation at 2.3 meV in the paraelectric up-up-down-down collinear magnetic phase, while this electromagnon vanishes in the ferroelectric helimagnetic phase. Anti-correlation with noncollinear magnetism excludes the exchange-striction mechanism as the origin of dynamical magnetoelectric coupling, and hence evidences the observation of spin-orbit coupling mediated electromagnon in the present compound.