Skyrmion-antiSkyrmion pairs in Ultracold Atomic Gases

We study theoretically the dynamics of two-component Bose-Einstein condensates in two dimensions, which admit topological excitations related to the Skyrmions of nuclear physics. We show that there exists a branch of uniformly propagating solitary waves characterised by a conserved momentum. These excitations exhibit a cross-over from spatially extended spin-wave states at low momentum to a localised "spin-wave droplet" at intermediate momentum; at still higher momentum, the configuration evolves continuously into a Skyrmion-antiSkyrmion pair. We discuss how these solitary waves can be generated and studied in experiment.