Axially Bound Magnetic Skyrmions: Glueing Topological StringsAcross an Interface

A major challenge in topological magnetism lies inthe three-dimensional (3D) exploration of their magnetic textures.A recent focus has been the question of how 2D skyrmion sheetsvertically stack to form distinct types of 3D topological strings.Being able to manipulate the vertical coupling should thereforeprovide a route to the engineering of topological states. Here, wepresent a new type of axially bound magnetic skyrmion string statein which the strings in two distinct materials are glued togetheracross their interface. With quasi-tomographic resonant elastic X-ray scattering, the 3D skyrmion profiles before and after theirbinding across the interface were unambiguously determined andcompared. Their attractive binding is accompanied by repulsive twisting; i.e., the coupled skyrmions mutually affect each other via acompensating twisting. This state exists in chiral magnet-magnetic thinfilm heterostructures, providing a new arena for theengineering of 3D topological phases