Current-induced vortex trapping in asymmetric toothed channels

We investigate experimentally and theoretically the vortex dynamics in a superconducting film with nanoengineered open vortex traps which provide tunable pinning, ranging from no pinning for a certain current direction to finite pinning when reversing the current flow. The design is based on the confinement of the vortex motion within two repulsive walls, one with periodic microprotrusions and the other one smooth. Clear commensurability effects are seen if the bias current drives the vortices inside the traps, whereas these effects are much less pronounced when the current pushes the vortices against the smooth surface. For small periods of the protrusions or large vortex sizes, the properties displayed by the vortices, pushed against these two surfaces of dissimilar roughness can be thought of as due to the change of effective sliding friction.