Magnetic skyrmion Walker breakdown in cylindrical nanotubes

As topological spin textures, magnetic skyrmions in chiral magnets show a universal current-velocity relation when driven by spin transfer torques. In general, the skyrmions in chiral magnets do not exhibit Walker breakdown---a phenomenon that domain walls' motion modes will change from steady to precessional motion when the driving forces are sufficiently large. In this work, we studied the dynamics of magnetic skyrmions in cylindrical nanotubes numerically and analytically. The skyrmion performs a helical motion in the nanotube without external fields. However, we show that the skyrmion exhibits the Walker breakdown phenomenon when an external field is applied to the nanotube perpendicularly. A steady skyrmion motion is observed in the low current regime, while the skyrmion moves forward and back when the current is larger than a critical density. Our findings reveal a new way to tune the skyrmion dynamics beyond planar geometries.