Fluxon manipulation by nanoscale artifcial pinning lattices in cuprate superconductors

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Superconductivity is an exciting phenomenon with many unresolved fundamental questions to be explored. Relevant experiments require to pattern superconductors on the nanoscale for a control of magnetic flux quanta, also called fluxons or vortices.The project aims at static and dynamic properties of vortices in cuprate high-Tc superconductor (HTSC) thin films patterned with tailored pinning landscapes of unprecedented density, complexity and minimum size of pinning sites. Theoretically proposed unconventional critical states, the relation of pinning potential vs defect size, vortex melting in artificial pinning arrays and transverse Hall commensurability effects will be investigated. Exploration of fluxon manipulation, potentially useful for devices, includes studies on high-velocity vortex dynamics, on complex pinning structures and on vortex ratchet effects.While the complicated crystal structure of the HTSCs pose a challenge to their technical usability, this project will turn this susceptibility into an asset to fabricate superconducting nanostructures with unprecedented resolution. In HTSCs, point defects are created by Helium ion irradiation with moderate energy that readily suppress the critical temperature. Using shadow projection of a wide-field ion beam through a stencil mask or the focused beam of a He ion microscope (HIM), it is possible to pattern nanoscale pinning landscapes into HTSCs. They will be further investigated by various experiments.Creating ultradense pinning lattices in HTSCs by irradiation in a HIM is a novel technique, for the first time demonstrated recently by the applicants. It allows to explore a hitherto inaccessible size and parameter range of strong fluxon coupling in artificial pinning lattices with lattice constants well below the London penetration depth. The experiments will test the achievable minimal length scales for nanofabrication of fluxon-related structures in HTSCs and, thus, provide important consequences for further research. Significant implications are expected on the understanding of vortex physics and on the development of new functional materials and ultrafast, low-dissipation superconducting circuits. This may lead to improved ultrasmall magnetic field sensors (SQUIDs) based on cuprate superconductors.The research will be performed by three partners with complementary expertise and equipment: W. Lang (University of Vienna), J. D. Pedarnig (Johannes Kepler University of Linz), and D. Kölle (Eberhard Karls Universität Tübingen). External collaborators will support the project with molecular-dynamic simulations of vortex arrangements and vortex dynamics (V. Misko, University of Antwerp) and with local probe techniques for the visualization of vortices (H. Suderow, Universidad Autónoma de Madrid).