  Non-collinear magnetic skyrmion lattices provide novel magnonic
functionalities due to their topological magnon bands and asymmetric dispersion
relations. Magnon excitations with intermediate wavelengths comparable to
inter-skyrmion distances are particularly interesting but largely unexplored so
far due to experimental challenges. Here, we report the detection of such
magnons with wavevectors q $\simeq$ 48 rad/um in the metastable skyrmion
lattice phase of the bulk chiral magnet Cu$_2$OSeO$_3$ using micro-focused
Brillouin light scattering microscopy. Thanks to its high sensitivity and broad
bandwidth we resolved various excitation modes of a single skyrmion lattice
domain over a wide magnetic field regime. Besides the known modes with dipole
character, quantitative comparison of frequencies and spectral weights to
theoretical predictions enabled the identification of a quadrupole mode and
observation of signatures which we attribute to a decupole and a sextupole
mode. Our combined experimental and theoretical work highlights that skyrmionic
phases allow for the design of magnonic devices exploiting topological magnon
bands.
