Ferromagnetic-Core Spin Vortex of Quasi-2D Spin-1 Condensate in a Harmonic Trap

We study the ferromagnetic (FM)-core spin vortex of spin-1 condensate in a 2D harmonic trap with homogeneous magnetic field. It is shown that such a topological excitation may exist when the system stays at the easy-axis phase with the negative quadratic-Zeeman-energy parameter larger than a critical value. The exact spatial distributions of number density and local spin are obtained with a variational method. A polar ring with local spin $F=0$ appears in the FM-core spin vortex. The density–density interaction can significantly affect both the spatial distribution of local spin and the position of the polar ring. The local spin in most areas is larger for the stronger ferromagnetic interaction. More interestingly, a local minimum emerges near the polar ring in the curve of total number density when the spin–spin interaction is large enough. In such easy-axis phase, the quadratic-Zeeman-energy parameter cannot control the FM-core spin vortex. An easily controlled experiment scheme is provided to realize the FM-core spin vortex.