Coupled-oscillator collective mode of a magnetic chiral soliton lattice

The collective excitation modes of a magnetic chiral soliton lattice (CSL) are numerically studied. We perform micromagnetic simulations of a monoaxial chiral helimagnet with an external magnetic field that forms the CSL. Due to the repulsive interaction between solitons through a ferromagnet state, collective modes described by the coupled oscillator are excited. These modes exist at a frequency of $\ensuremath{\sim}1\phantom{\rule{0.28em}{0ex}}\mathrm{GHz}$ while the conventional ferromagnetic resonant mode exists at a frequency of $\ensuremath{\sim}10\phantom{\rule{0.28em}{0ex}}\mathrm{GHz}$ as measured in experiments [F. Goncalves et al., Phys. Rev. B 95, 104415 (2017)]. In contrast to ferromagnetic resonance, the resonant frequency of the coupled-oscillator mode decreases by increasing the magnetic field. We clarified that the coupling energy between solitons becomes weak by increasing the distance between solitons. We also investigate the resonant condition of a precessional mode of the CSL measured in experiments.