Instabilities of a Filled Vortex in a Two-Component Bose–Einstein Condensate

A two-component Bose–Einstein condensate of cold atoms with a strong intercomponent repulsion leading to the spatial separation of the components has been numerically studied. Configurations with a multiple quantized vortex in one component, where the vortex core is filled with the other component, are considered. The effective radius of the core can exceed the width of the transition layer between components, and then an analogy with a filled cylindrical vortex in the classical hydrodynamics of two immiscible ideal fluids appears. This analogy allows one to analyze the longitudinal “sausage” instability and the transverse instability of the filled vortex in the condensate caused by the “tangential discontinuity,” as well as the stable regime in the parametric gap between them. The presence of long-lived coherent structures formed in some cases at the nonlinear stages of both instabilities is numerically discovered.