Different approaches to generate matching effects using arrays in contact with superconducting films

TL;DR

This study investigates how different array configurations and materials in contact with superconducting Nb films influence vortex pinning and matching effects, revealing the importance of array order and magnetic properties.

Contribution

It introduces various array configurations and materials to analyze their effects on vortex pinning and matching phenomena in superconducting films, highlighting the role of array order and magnetic pinning.

Findings

Periodic roughness induces resistivity minima.

Magnetic pinning has a minor effect on matching effects.

Array order is crucial for maintaining magnetoresistance minima.

Abstract

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.