  A vortex lattice ratchet effect has been investigated in Nb films grown on
arrays of nanometric Ni triangles, which induce periodic asymmetric pinning
potentials. The vortex lattice motion yields a net dc-voltage when an ac
driving current is applied to the sample and the vortex lattice moves through
the field of asymmetric potentials. This ratchet effect is studied taking into
account the array geometry, the temperature, the number of vortices per unit
cell of the array and the applied ac currents.
