  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
understanding its abundant low-temperature magnetically ordered phases.
