Phase diagram for ultracold bosons in double-well optical lattices

We study the superfluid-Mott insulator transition of bosons in double-well optical lattices. Applying a mean-field approximation to the Bose-Hubbard Hamiltonian, we obtain the zero-temperature phase diagram and find that there exist the half-integer-filling and integer-filling Mott insulator domains in the phase diagram. We show that the half-integer-filling Mott insulator phase is stabilized as the intra-well hopping energy increases. We also calculate the phase diagram by employing the time evolving block decimation (TEBD) algorithm and compare the results obtained from the mean-field approximation with those from the TEBD.