Observation of coherent helimagnons in the Skyrmionic helimagnets*

In MnSi and Fe$_{1-x}$Co$_{x}$Si the interplay between the spin-orbit and exchange interactions leads to a variety of helical magnetically ordered states. Perhaps the most interesting of these is the Skyrmion lattice phase in which the spins form topologically-stabilized vortices which decouple from the host lattice to form their own lattice structure. We use pump-probe reflectivity and Kerr rotation to study the dynamics in these materials, observing coherent collective excitations unique to helimagnets known as helimagnons. Monitoring helimagnon decay in the time-domain directly yields the Gilbert damping parameter in these systems.