Superfluid-Mott Insulator Transition of Spin-1 Bosons in an Optical   Lattice
  We have studied superfluid-Mott insulating transition of spin-1 bosons interacting antiferromagnetically in an optical lattice. We have obtained the zero-temperature phase diagram by a mean-field approximation and have found that the superfluid phase is to be a polar state as a usual trapped spin-1 Bose gas. More interestingly, we have found that the Mott-insulating phase is strongly stabilized only when the number of atoms per site is even. 
Shunji Tsuchiya, Susumu Kurihara, and Takashi Kimura