Half-quantum vortex state in a spin-orbit-coupled Bose-Einstein condensate

We theoretically investigate the condensate state and collective excitations of a two-component Bose gas in a two-dimensional harmonic trap subject to isotropic Rashba spin-orbit coupling. In the weakly interacting regime when the interspecies interaction is larger than the intraspecies interaction (g↑↓>g), we find that the condensate ground state has a half-quantum angular momentum vortex configuration with spatial rotational symmetry and skyrmion-type spin texture. Upon increasing the interatomic interaction beyond a threshold gc, the ground state starts to involve higher-order angular momentum components and thus breaks rotational symmetry. In the case of g↑↓gc and g↑↓