Non-Reciprocal Zone Boundary Magnon Propagation in Cu$_2$OSeO$_3$

Inelastic neutron scattering in the chiral magnet Cu$_2$OSeO$_3$ reveals strong non-reciprocal effects on magnon propagation at the boundary of the nuclear Brillouin zone. The non-reciprocal response is strongest at a central position between the zone corner and edge mid-point. We explain these results using an effective linear spin-wave model. While directional effects in chiral magnets have so far only been known to exist at low momenta close to the center of the Brillouin zone, the present study shows that non-reciprocity persists at the highest possible reduced momenta. The observed magnons show very little damping within the limits of our experimental resolution, making them of great interest for the fundamental research on compact, high-frequency magnonic applications.

💡 Research Summary

In this work the authors investigate non‑reciprocal (NR) magnon propagation in the chiral insulator Cu₂OSeO₃ at the highest reduced momenta accessible in a crystal, namely at the nuclear Brillouin‑zone boundary. Using inelastic neutron scattering on a large (≈5 g) single crystal, they measured the dynamical structure factor S(q,E) along the (1.5, 1.5, l) direction (M–R line) at 10 K under a vertical magnetic field of 0.4 T. By reversing the field direction (B‖