Non-reciprocal spin excitations across the skyrmion–paramagnetic phase transition in MnSi

The magnetic excitations of the skyrmion lattice in MnSi comprise a multitude of individual modes, which are non-reciprocal and thereby propagate unidirectionally. We report inelastic neutron scattering experiments for temperatures near and above the skyrmion–paramagnetic phase transition in the chiral magnet MnSi, tracking the evolution from the skyrmion lattice towards the high-temperature paramagnetic state. Within the resolution of the triple-axis measurements the excitations vary smoothly across the skyrmion–paramagnetic boundary, and the quasi-elastic paramagnetic signal under applied field retains the non-reciprocal character seen in the skyrmion phase even far above the critical temperature. Using a resolution convolution, our results are consistent with linear spin-wave theory.