# Polarized inelastic neutron scattering of non-reciprocal spin waves in MnSi

## TL;DR

This study uses polarized inelastic neutron scattering to investigate non-reciprocal spin waves in MnSi, revealing directional differences in spectral weight distribution and confirming theoretical predictions of non-reciprocal magnetic responses.

## Contribution

It provides the first detailed experimental observation of non-reciprocal spin wave spectral weight distribution in MnSi, aligning with theoretical models without adjustable parameters.

## Key findings

- Spectral weight concentrates on single branches along the helix axis.
- Spectral weight is distributed among multiple branches perpendicular to the helix.
- Experimental results match theoretical predictions quantitatively.

## Abstract

We report spin-polarized inelastic neutron scattering of the dynamical structure factor of the conical magnetic helix in the cubic chiral magnet MnSi. We find that the spectral weight of spin-flip scattering processes is concentrated on single branches for wavevector transfer parallel to the helix axis as inferred from well-defined peaks in the neutron spectra. In contrast, for wavevector transfers perpendicular to the helix the spectral weight is distributed among different branches of the magnon band structure as reflected in broader features of the spectra. Taking into account the effects of instrumental resolution, our experimental results are in excellent quantitative agreement with parameter-free theoretical predictions. Whereas the dispersion of the spin waves in MnSi appears to be approximately reciprocal at low energies and small applied fields, the associated spin-resolved spectral weight displays a pronounced non-reciprocity that implies a distinct non-reciprocal response in the limit of vanishing uniform magnetization at zero magnetic field.