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

Tobias Weber, Niclas Heinsdorf, Michal Stekiel, Paul Steffens, Andreas Schnyder, Christian Pfleiderer

Abstract

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.

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

Abstract

Inelastic neutron scattering in the chiral magnet CuOSeO 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.

Paper Structure

This paper contains 1 equation, 1 figure, 1 table.

Figures (1)

  • Figure 1: Non-reciprocal zone-boundary magnon dispersion. (a) Theoretical dispersion relation along the cubic zone boundary at $\mathbf{Q} = \left(1.5, \ 1.5, \ l \right)$ between the $M$ and the $R$ point for two field directions that are $180^{\circ}$ apart. The thickness of the lines signifies the spin-spin correlation function, which gives the spectral weight of a magnon mode. The positions of the individual scans are marked as gray vertical bars. (b) Energy shifts $\Delta E_{NR} = \left|E \left(q \right)\right| - \left|E \left(-q \right)\right|$ of the magnon bands due to non-reciprocity. (c) Cubic Brillouin zone, $M$, $R$, and $Z$ symmetry points and accessible zone cut within the scattering plane (inset). The scan path is marked with an arrow. (d)-(i) Data measured at Thales (points), where the typical measurement time per point was about two minutes. The field directions $\mathbf{B} \parallel \left[ 00\bar{1} \right]$ and $\mathbf{B} \parallel \left[ 001 \right]$ are shown in blue and red, respectively. The solid lines show the resolution-convolution fit of the theory and the data. The black lines in the top-right corners denote the incoherent and the coherent resolution at $E = 10\ \mathrm{meV}$, respectively.