  Controlling multiple skyrmions in nanowires is important for their
implementation in racetrack memory or neuromorphic computing. Here, we report
on the dynamical behavior of two interacting skyrmions in confined devices with
a comparison to a single skyrmion case. Although the two skyrmions shrink near
the edges and follow a helical path, their behavior is different. Because the
leading skyrmion is between the edge and the trailing one, its size is reduced
further and collapses at a lower current density compared to the single
skyrmion case. For higher current density, both skyrmions are annihilated with
a core-collapse mechanism for the leading one followed by a bubble-collapse
mechanism for the trailing one.
