Chiral Magnons in the Collinear Antiferromagnet α-Fe₂O₃

Collinear antiferromagnets (AFMs) are known to exhibit two distinct chiral magnons, left-handed and right-handed. Such a feature of AFMs is distinguished from the case of ferromagnets (FMs) where only right-handed magnons are excited. Naturally, chiral magnons as information carriers are of great interest in spintronic applications. However, a means to directly observe the chirality of magnons is still lacking. Here, we demonstrate a direct observation of the magnon chirality in α-Fe₂O₃ in its collinear phase by using terahertz time-domain spectroscopy. When chiral magnons interact with circularly polarized light, they behave differently according to the chirality of the terahertz photon. By using this selection rule of the magnon excitation, we successfully identified two distinct magnons in the terahertz regime. Our results would be helpful to future understanding and application of the handedness of magnons in general.