Fractional spin-vortex states in F = 2 spinor Bose-Einstein condensates

Stable fractional vortices are numerically generated in the two-dimensional rotating F=2 spinor Bose-Einstein condensates. We demonstrate the existence of 14-vortex state or 12-vortex state in the biaxial nematic phase, and 13-vortex state in the cyclic phase. At fast rotation a lattice of fractional vortex in the spin space emerges. Intriguingly, the integral spin-winding of the whole system does not increase with the rotation speed but equals to a simple fraction.