  Superconducting films in contact with non-superconducting regular arrays can
exhibit commensurability effects between the vortex lattice and the unit cell
of the pinning array. These matching effects yield a slowdown of the vortex
flow and the corresponding dissipation decrease. The superconducting samples
are Nb films grown on Si substrates. We have studied these matching effects
with the array on top, embedded or threading the Nb superconducting films and
using different materials (Si, Cu, Ni, Py dots and dots fabricated with Co/Pd
multilayers). These hybrids allow studying the contribution of different
pinning potentials to the matching effects. The main findings are: i) Periodic
roughness induced in the superconducting film is enough to generate resistivity
minima; ii) A minor effect is achieved by magnetic pinning from periodic
magnetic field potentials obtained by dots with out of plane magnetization
grown on top of the superconducting film, iii) In the case of array of magnetic
dots embedded in the films vortex flow probes the magnetic state; i.e.
magnetoresistance measurements detect the magnetic state of very small
nanomagnets. In addition, we have studied the role played by the local order in
the commensurability effects. This was attained using an array that mimics a
smectic crystal. We have found that preserving the local order is crucial. If
the local order is not retained the magnetoresistance minima vanish.

Superconductivity