Vortex lattice channeling effects in Nb films induced by anisotropic arrays of mesoscopic pinning centers

Rectangular arrays of Ni dots with small interdot separation have been fabricated in superconducting Nb films. The geometry of these rectangular arrays defines deep pinning potential channels. Two effects have been observed. (i) When the vortices move perpendicular to the channels (i.e., along the long side of the rectangular array) an enhancement of the background pinning is observed, as predicted by theoretical models. This enhancement occurs for all magnetic fields. (ii) A new anisotropic matching effect, which has not been theoretically predicted, has been measured. The position of the matching fields depends on the direction of the vortex flow. When the vortices move parallel to the potential channels (i.e., along the short side of the rectangular array) the vortex lattice matches the rectangular array, but when they move along the long side of the rectangular array only a triangular lattice is observed.