Commensurability Effects and Long-Term Stability of Pinning Landscapes in Copper-Oxide Superconductors Fabricated by Focused He-Ion-Beam Nanopatterning

Description

The focused beam of a helium ion microscope (HIM) is an excellent tool for creating closely spaced nanocolumns in thin films of copper-oxide superconductors [1]. Within these nanocolumns, the critical temperature Tc is reduced or entirely suppressed due to the disruption of the superconducting charge carrier pairs by scattering on numerous point defects. Most irradiation-induced displacements affect oxygen atoms while not reducing the overall oxygen content in the sample. It is widely accepted that the oxygen atoms are displaced only a few unit cells, which implies that moving back only requires minimal energy.

To optimize the conditions for creating nanostructures suitable as Abrikosov-vortex pinning arrays via focused He+-beam irradiation (He-FIB), we have investigated the impact of various irradiation parameters on the structural and superconducting properties of YBa₂Cu₃O_7-δ (YBCO) thin films. An important point is the optimal number of 30 keV He+ ions needed to irradiate a dot of the nanocolumn lattice for maintaining the crystalline framework of YBCO intact while suppressing its superconductivity. Using aberration-corrected scanning transmission electron microscopy, we identified a critical dose of approximately 13,000 ions/dot beyond which the YBCO film becomes amorphous. Conversely, lower doses do not cause any visible damage. Still, they affect the behavior of magnetic flux quanta, influencing the efficiency of the vortex pinning lattices formed by the columnar defects [1]. Moreover, we demonstrate that the He-FIB technique can also be applied to Bi₂Sr₂CaCu₂O_8+x thin films to produce efficient pinning landscapes in this highly anisotropic superconductor.

One topic to be investigated is the stability of these defects over long timescales. To address this, we investigated the efficiency of pinning arrays in YBCO films over several years of storage at room temperature. The critical temperature Tc increased during an initial healing period of about three years and then showed a marginal decrease up to a total storage period of almost six years. The long-term storage in dry air did not compromise the vortex-matching signatures. This analysis suggests that room-temperature annealing reduced the defect density surrounding the columnar defect channels while maintaining robust pinning potential at their cores [2]. Our results carry significant implications for potential applications in fluxonics.

[1] M. Karrer, B. Aichner, K. Wurster, C. Magén, C. Schmid, R. Hutt, B. Budinská, O.V.Dobrovolskiy, R. Kleiner, W. Lang, E. Goldobin, D. Koelle, Phys. Rev. Applied, 22 (2024) 014043.
[2] S. Keppert, B. Aichner, P. Rohringer, M.-A. Aurel Bodea, B. Müller, M. Karrer, R. Kleiner, E. Goldobin, D. Koelle, J. D. Pedarnig, W. Lang, Int. J. Mol. Sci., 25 (2024) 7877.

Acknowledgments
The research was funded by a joint project of the Austrian Science Fund (FWF), grant I4865-N, and the German Research Foundation (DFG), grant KO 1303/16-1. It is based upon work from COST Actions CA19140 (FIT4NANO), CA21144 (SuperQuMap), and CA19108 (Hi-SCALE) supported by COST (European Cooperation in Science and Technology). B.A. acknowledges financial support from the Austrian Science Fund, grant I6079.

Period	2 Oct 2024
Event title	10th International Conference on Materials Science and Condensed Matter Physics
Event type	Conference
Location	Chișinău, Moldova, Republic ofShow on map
Degree of Recognition	International