Half-knot in the spinor condensates

We present an exact solution to the stationary coupled nonlinear Gross-Pitaevskii equations which govern the motion of the spinor Bose-Einstein condensates. The solitonic solution is a twisted half-skyrmion in the three-dimension (3D) space. By making a map from and the Cartesian coordinates to the toroidal coordinates, we demonstrate it is a linked half-unknot with a fractional Hopf charge.