Critical depinning and collective dynamics of magnetic skyrmion lattices

The dynamic phases of skyrmion matter govern both its fundamental behaviour and its potential for applications. While theoretical studies and simulations have predicted rich collective dynamics, theis has so far remained largely unexplored experimentally in real materials. Here we report time-resolved small-angle neutron-scattering measurements of skyrmion lattice (SkL) dynamics in insulating Cu₂OSeO₃, driven by a radial magnon current in a Corbino geometry. The magnon current induces a rotation of the macroscopically coherent SkL, whose angular velocity decreases with increasing magnetic field. By tuning the field, and thereby the SkL elastic moduli, we approach a collective depinning transition in which the system evolves from a smoothly rotating state with a constant angular velocity, to an intermittent regime of alternating rotating and stationary states. In addition, the frequency and duration of stationary states indicating a stochastic depinning when the system re-enters the rotating state. Similar collective dynamics are known from other soft condensed matter systems of interacting particles, all pointing to universal depinning physics.