Phase-separation of vector solitons in spin-orbit coupled spin-1 condensates

Abstract: We study the phase-separation in three-component bright vector solitons in a quasi-one-dimensional spin-orbit-coupled hyper-fine spin $F=1$ ferromagnetic Bose-Einstein condensate upon an increase of the strength of spin-orbit (SO) coupling $p_x \Sigma_z$ above a critical value, where $p_x$ is the linear momentum and $\Sigma_z$ is the $z$-component of the spin-1 matrix. The bright vector solitons are demonstrated to be mobile and dynamically stable. The collision between two such vector solitons is found to be elastic at all velocities with the conservation of density of each vector soliton. The two colliding vector solitons repel at small separation and at very small colliding velocity, they come close and bounce back with the same velocity without ever encountering each other. This repulsion produced by SO coupling is responsible for the phase separation in a vector soliton for large strengths of SO coupling. { The collision dynamics is found to be completely insensitive to the relative phase of the colliding solitons.} However, in the absence of SO coupling, at very small velocity, the two colliding vector solitons attract each other and form a vector soliton molecule and the collision dynamics is sensitive to the relative phase as in scalar solitons. The present investigation is carried out through a numerical solution and an analytic variational approximation of the underlying mean-field Gross-Pitaevskii equation.