Ultradense Tailored Vortex Pinning Arrays in Superconducting YBa₂Cu₃O_7−δ Thin Films Created by Focused He Ion Beam Irradiation for Fluxonics Applications

Magnetic fields penetrate a type II superconductor as magnetic flux quanta, called vortices. In a clean superconductor they arrange in a hexagonal lattice, while by addition of periodic artificial pinning centers many other arrangements can be realized. Using the focused beam of a helium ion microscope, we have fabricated periodic patterns of dense pinning centers with spacings as small as 70 nm in thin films of the cuprate superconductor YBa₂Cu₃O_7−δ. In these ultradense kagomé-like patterns, the voids lead to magnetic caging of vortices, resulting in unconventional commensurability effects that manifest themselves as peaks in the critical current and minima in the resistance versus applied magnetic field up to ∼0.4 T. The various vortex patterns at different magnetic fields are analyzed by molecular dynamics simulations of vortex motion, and the magnetic field dependence of the critical current is confirmed. These findings open the way for a controlled manipulation of vortices in cuprate superconductors by artificial sub-100 nm pinning landscapes.