Exotic Spin Excitations in a Polar Magnet VOSe_{2}O_{5}.

Magnetic resonance dynamics has been studied for a polar magnet VOSe_{2}O_{5}, which hosts several nontrivial magnetic phases including Néel-type skyrmion lattice (SkL). In both cycloidal and SkL spin states, two excitation modes active to oscillating magnetic field B_{ν}⊥c and one mode active to B_{ν}∥c are identified. The subsequent micromagnetic simulations well reproduce the observed selection rules and relative resonance frequencies, which allows the unambiguous assignment of the spin oscillation manner for each mode. Interestingly, the IC-2 phase with a potential double-q character was found to host similar excitation modes as the SkL state. We also discovered the existence of the novel B' phase with four modes active to B_{ν}⊥c. The present results provide a fundamental basis for the comprehensive understanding of resonant spin dynamics in polar magnets, and highlight VOSe_{2}O_{5} as a unique material platform to host a rich variety of nontrivial spin excitations.