Vortex-Antivortex Lattices in Superconducting Films with Magnetic Pinning Arrays

TL;DR

This paper reports the discovery of novel vortex-antivortex lattice structures in superconducting films with magnetic dot arrays, revealing unique phase transitions and an unconventional increase in critical current under external magnetic fields.

Contribution

It introduces the formation of vortex-antivortex lattices in superconducting films with magnetic pinning arrays and explores their phase transitions and effects on critical current.

Findings

Vortex-antivortex lattices form in superconducting films with magnetic dot arrays.

Phase transitions occur as the array density or magnetization changes.

Critical current increases with external magnetic field, contrary to typical behavior.

Abstract

Novel vortex structures are found when a thin superconducting film (SC) is covered with a lattice of out-of-plane magnetized magnetic dots (MDs). The stray magnetic field of the dots confines the vortices to the MD regions, surrounded by antivortices which "crystallize" into regular lattices. First and second order transitions are found as magnetic array is made sparser or MD-magnetization larger. For sparse MD-arrays fractional vortex-antivortex states are formed, where the crystal-symmetry is combined with a non-uniform "charge" distribution. We demonstrate that due to the (anti)vortices and the supercurrents induced by the MDs, the critical current of the sample actually increases if exposed to a homogeneous external magnetic field, contrary to conventional SC behavior.