The CMT group has contributed as part of an international collaboration to the development of a heterostructure that achieves stable skyrmion-vortex coexistence, with control over the coupling between these two topological excitations. The researchers experimentally study the interactions between a magnetic [Ir/FeCo/Pt] sandwich structure that can host skyrmions and a superconducting niobium (Nb) layer that is either in direct contact with the magnet or separated by a thin insulating MgO layer. A small applied magnetic field nucleates in the sandwich-structure skyrmions that have spins that rotate in the radial plane from the core to the periphery. Stray magnetic fields from the skyrmions induce vortices in the Nb film, which were observed with scanning tunneling spectroscopy.

The researchers explain the mechanism for the skyrmion-vortex induction in terms of an effect observed when a two-dimensional electron gas at an interface becomes spin polarized. This spin polarization leads to spin accumulation and, because of spin-orbit coupling, a charge current at the interface. Whether the spin polarization is induced by the exchange coupling in direct contact between the magnetic and superconducting layers or just by the stray magnetic field, it can be regulated by the presence or absence of the intervening insulator layer. Since temperature alters the ratio of the superconductor vortex radius to the skyrmion radius (each around 50 nm), the coupling strength can be tuned.

Read further in Physics Viewpoint article detailing the research.

This research was published in Phys. Rev. Lett. 126, 117205 (2021).