Dynamics and topological mass of skyrmionic spin structures (presentation video)

Skyrmions are topologically protected particle-like configurations, with a topological complexity described by their Skyrmion number. In magnetic systems, they have been numerically predicted to exhibit rich dynamics, such as the gyrotropic and breathing modes, dominated by their topology. Recent experimental advances brought their static manipulation well under control. However, their dynamical behaviour is largely unexplored experimentally. In this work, we provide with the first direct observation of eigenmode skyrmion dynamics. In particular, we present dynamical imaging data with high temporal and spatial resolution to demonstrate the GHz gyrotropic mode of a single skyrmion bubble, as well as the breathing-like behaviour of a pair of skyrmionic configurations. We use the observed dynamical behaviour to confirm the skyrmion topology and show the existence of an unexpectedly large inertia that is key for accurately describing skyrmion dynamics. Our results demonstrate new ways for experimentally observing skyrmion dynamics and provide a framework for describing their behaviour. Furthermore, the results outline a link between the dynamical behaviour of skyrmions and their distinct topological properties, with possible ramifications for skyrmionic spin structures research including technological applications.