Multi-vortex versus interstitial vortices scenario in superconducting antidot arrays

TL;DR

This paper investigates vortex behavior in superconducting NbN antidot arrays, comparing scenarios where multiple vortices occupy antidots versus interstitial sites, and explores vortex reordering under different conditions.

Contribution

It provides experimental insights into vortex arrangements in NbN antidot arrays, highlighting the competition between multi-vortex and interstitial vortex scenarios at various matching fields.

Findings

Evidence of vortex occupation on antidots at higher matching fields.

Observation of interstitial vortex nucleation and reordering.

Dependence of vortex behavior on lattice geometry and superconducting parameters.

Abstract

In superconducting thin films, engineered lattice of antidots (holes) act as an array of columnar pinning sites for the vortices and thus lead to vortex matching phenomena at commensurate fields guided by the lattice spacing. The strength and nature of vortex pinning is determined by the geometrical characteristics of the antidot lattice (such as the lattice spacing $a_0$, antidot diameter $d$, lattice symmetry, orientation, etc) along with the characteristic length scales of the superconducting thin films, viz., the coherence length ($\xi$) and the penetration depth ($\lambda$). There are at least two competing scenarios: (i) multiple vortices sit on each of the antidots at a higher matching period, and, (ii) there is nucleation of vortices at the interstitial sites at higher matching periods. Furthermore it is also possible for the nucleated interstitial vortices to reorder under suitable conditions. We present our experimental results on NbN antidot arrays in the light of the above scenarios.