Magnon spectrum of the helimagnetic insulator Cu2OSeO3

Complex low-temperature ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu2OSeO3 became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering (INS) to comprehend the full three-dimensional spin excitation spectrum of Cu2OSeO3 over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison of our INS data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu2OSeO3 that are essential for understand-ing its abundant low-temperature magnetically ordered phases. Introduction. Chiral magnets form a broad class of mag-netic materials in which long-range dipole interactions, mag-netic frustration, or relativistic Dzyaloshinskii-Moriya (DM) interactions twist the initially ferromagnetic spin arrange