Vortex Matter in Nanostructured and Hybrid Superconductors

Wednesday, October 27, 2004 - 11:00am - 11:50am
EE/CS 3-180
Francois Peeters (Universiteit Antwerp)
The interplay between superconductivity and the inhomogeneous magnetic field generated by nanostructured ferromagnets leads to new vortex arrangements not found in homogeneous superconductors. We consider two situations: 1) a ferromagnetic disk on top of a thin superconducting film, and 2) a lattice of such ferromagnetic disks separated by a thin oxide layer on top of a thin superconducting film.

For a single ferromagnetic disk magnetized perpendicular to the plane of the superconducting film we found that antivortices are stabilized in shells around a central core of vortices (or a giant vortex) with size/magnetization-controlled `magic numbers.' The transition between the different vortex phases occurs through the creation of a vortex-antivortex pair under the edge of the magnetic disk. In the case of a lattice of ferromagnetic disks, the antivortices form a rich spectrum of lattice states. In the ground state the antivortices are arranged in the so-called matching configurations between the ferromagnetic disks while the vortices are pinned to the ferromagnets. The exact (anti)vortex structure depends on the size, thickness and magnetization of the magnetic dots, periodicity of the ferromagnetic lattice and properties of the superconductor expressed through the effective Ginzburg-Landau parameter *. The experimental implications of our results such as magnetic-field-induced superconductivity will be discussed.

The theoretical analysis is based on a numerical .exact. solution of the phenomenological Ginzburg-Landau equations.