Proximity effects and vortex dynamics in superconducting heterostructures

Vortex lattice dynamics has been studied in thin Nb superconducting films sputtered on top of a dense triangular array of V dots with and without an intermediate SiO2 insulating layer. While the insulating layer modifies only slightly the Nb film corrugation, it reduces superconducting commensurability effects (CE) substantially. This implies that superconducting commensurability is dominated by proximity effects. Moreover, the HC2 (T) phase diagram of the sample without an insulating layer shows a parabolic temperature dependence near TC and critical temperature oscillations with the periodicity of the matching field. Therefore, strong proximity effects locally suppress superconductivity leading to a superconducting mesh. When the proximity effect is decreased by an insulating layer, HC2(T) follows the expected linear T dependence.