Topological Hall effect induced Skyrmion-Antiskyrmion coupling in inhomogeneous racetrack

In this paper we investigate a magnetic racetrack consisting of a junction of three materials with different properties. Indeed, this magnetic system is composed by two distinct regions (racetracks) connected by a thin interface: the first region (termed sector $1$) has isotropic in-plane magnetic chirality and supports skyrmion ($S$) excitations while the second (sector $3$) has anisotropic chirality and consequently supports antiskyrmions ($A$). The interface, which would be a third region (sector $2$, connecting sectors $1$ and $3$) located in the central part of the racetrack, is an easy-axis Heisenberg ferromagnetic material. The topological structures $S$ and $A$ are put in motion by applying a spin-polarized current. Under certain conditions, we show that the skyrmion and the antiskyrmion created in their respective sectors are simultaneously impelled to the interface (due to the Magnus force) to apparently become a unique object (a skyrmion-antiskyrmion pair or $SAP$). After glued by sector $2$, the skyrmion and the antiskyrmion move together (as a $SAP$) along the direction of the applied current. It is also shown that such an engineered racetrack can support a sequence of several $SAP$ structures in motion, forming a current.