Topological defects and the 2D superfluid transition in $S=1$ spinor condensates

Condensates of non-zero spin have recently attracted a lot of interest both theoretically and experimetally. The spin degree of freedom can give rise to interesting magnetically ordered phases. This talk will focus on condensates of Spin-1 atoms ($^{23}$Na, $^{87}$Rb). These will be shown to have intresting ground state manifolds and topological defects. The toplogical defects play an important role in the superfluid transition in two dimensions. The low temperature phase of $^{23}$Na will be shown to be a spin disordered nematic superfluid of boson pairs. The superfluid transition is of the Kosterlitz-Thouless type but mediated by half vortices. Extensions of these ideas to higher spin systems will be discussed. Journal Ref: Phys. Rev. Lett. 97, 120406 (2006)