Displaceable magnetic skyrmions in ultrathin films on superconductors for configurable Majorana state

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Isolated skyrmions are of particular interest for magnetic memories since they can be moved by low current densities and their topologically enhanced stability. They have been observed in a wide range of polycrystalline metallic multilayers. However, in these polycrystalline metallic films, skyrmion mobility is often limited by pinning to structural defects. For epitaxial films, only few systems are known to stabilize magnetic skyrmions. Among them are the structures where the spatial inversion symmetry is broken in the bulk by the crystal structure itself, as in MnSi, or by interfaces such as Fe/Ir(111). In these systems, isolated skyrmions were reported under large magnetic fields (1 to 3 T). We recently discovered that magnetic skyrmions in Co/Ru(0001) are meta stable down to vanishing magnetic fields and can be moved when observed with magnetic STM tip. Ru is, however, superconducting below 500 mK and at magnetic fields below 7 mT, and it has been suggested that at the interface between a conventional superconductor and magnetic films displaying Skyrmions, Majorana fermions are formed. The main objectives of this project is to realize and theoretically describe Majorana states in the hybrid non-collinear magnetic-superconducting system Co/Ru(0001) or related systems, to laterally displace the observed skyrmions and associated Majorana states with help of STM, to understand the mechanism of the lateral displacement, to investigate the proximity effect in the magnetic layer and the evolution of the Majorana states. Ultimately, the entanglement of Majorana states and the braiding of the Majorana zero modes will be studied in order to investigate the potential to use skyrmions in Co/Ru as for topological quantum computing. The project relies on a close collaboration between experiment and theory. The partners have collaborated on the purely magnetic aspects of the materials system, before.