Fabrication of Nanostructures for Advanced Vortex Pinning in High-T_c Superconductors

Description

The controlled fabrication of dense defect structures suitable for pinning Abrikosov vortices is challenging in high-T_c cuprate superconductors since conventional etching techniques are only poorly applicable. Nevertheless, controlling the motion of vortices is essential for applying superconductors in electronic devices. This urges the need for a process that allows for the fabrication of vortex pinning structures precisely and reproducibly in these materials.
A novel way of creating artificial pinning structures in cuprate superconductors, such as YBa₂Cu₃O_7-δ, is to locally suppress the material’s critical temperature T_c by irradiation with helium ions in a helium ion microscope. With this method, it is possible to create defect clusters that can accommodate one or more magnetic vortices. This leads to vortex-matching effects, i.e., pronounced maxima in the critical current and minima in resistivity at the magnetic field values, for which the vortex lattice is commensurate to the defect lattice. These matching fields depend on the distance between the defect clusters, and due to the high resolution achievable with He ion irradiation, we succeeded in creating regular defect arrays with matching fields up to 6 T. To our knowledge, this is the highest matching field ever reported for regular artificial pinning arrays in cuprate superconductors.
Simulations of the T_c-suppression show that the defect clusters created in the helium ion microscope are column-shaped and penetrate the whole superconducting film for typical film thicknesses of 30 to 50 nm. The one-dimensional shape of the defect columns also shows up in vortex pinning, as verified by angle-resolved measurements [1]. A thorough analysis of current-voltage characteristics suggests that a new vortex phase appears in these arrangements, which we identified as an ordered Bose glass phase [2].
One significant advantage of the helium ion microscope is the free choice of the irradiation pattern. This allowed us to create pinning arrays based on a quasi-kagomé pattern, which enables reproducibly switching between two stable vortex arrangements by changing the temperature [3].
Altogether, these findings establish the helium ion microscope as a promising tool for nanofabrication that allows us to create vortex-pinning structures of unprecedented density.

References
1. B. Aichner et al., Low Temperature Physics/Fizika Nizkikh Temperatur, 46, 331 (2020).
2. L. Backmeister et al., Nanomaterials, 12, 3491 (2022).
3. B. Aichner et al., ACS Applied Nano Materials, 2, 5108 (2019).

Period	6 May 2023
Event title	8th International Conference on Superconductivity and Magnetism - ICSM2023
Event type	Conference
Location	Fethiye, TurkeyShow on map
Degree of Recognition	International