Vortex molecules in a spin–orbit-coupled spin-1 condensate

A vortex molecule is predicted in a spin–orbit-coupled spin-1 Bose–Einstein condensate. This type of asymmetric soliton features four off-axis vortices and none of them coincide. There are two vortices of the same charge in the first and the third component, respectively, and two vortices of the opposite charge in the second component. This particular arrangement of vortices constitute a spin vortex molecule which is connected by a domain wall in the spin texture. In the dynamical simulation, we find the vortex molecule is static at the equilibrium but vibrates once it deviates from the equilibrium. The vibration mechanism is identified: fragmentation and coalescence. The vortex molecule exhibits mixing of ferromagnetic and antiferromagnetic states, where the meron-pair or bimeron is hidden. Our results suggest a way of creating bimeron-like vortex molecules in spin-1 Bose–Einstein condensates.