Landau versus Spin Superfluidity in Two Component Bose-Einstein Condensates

We consider two component Bose-Einstein condensates prepared in a single spin projection. In that case, density and spin waves can be described as distinct elementary excitations. This gives rise to separate critical velocities for the breakdown of the motional and the spin superfluidity. We demonstrate this behavior considering the interaction of the condensate with both a mechanical and a magnetic defect and calculate the corresponding drag forces.