Phase separation and vortex states in binary mixture of Bose-Einstein condensates

The phase separation and vortex states in two-component Bose-Einstein condensate consisting of $|F=1,m_f=-1>$ and $|2,1>$ internal spin states of $^{87}Rb$ atoms are considered in the framework of Thomas-Fermi approximation. It is shown that in nonrotating system the atoms in the state $|1,-1>$ form a shell about the atoms in the state $|2,1>$. The critical angular velocity for each state is calculated. These velocities are drastically dependent on the mutual concentrations of the components, the critical angular velocity of the outer component being less than the angular velocity of the inner one. It is shown that the atoms in the $|1,-1>$ state can form a rotating ring about the resting core of the atoms in the state $|2,1>$.