Observation of Chiral Magnon Band Splitting in Altermagnetic Hematite

Altermagnets, a new frontier for spintronics, represent a distinct magnet class with nonrelativistic splitting of both electronic and chiral magnon bands, yet experimental verification of their unique magnon dynamics remains scarce. In this Letter, inelastic neutron scattering experiments on α-Fe_{2}O_{3} reveal a clear magnon band splitting about 3 meV at ∼100  meV. We trace the origin of this splitting to the alternating exchange interactions between the 13th nearest neighbors, as supported by first-principles calculations, and confirm that the magnons have chiral splits by theoretical modeling. This definitive characterization of chiral magnons in hematite provides the fundamental insight needed to design and control spin transport in novel spintronic applications.