arXiv:1210.2322 · Physical Review A
Strong-coupling expansion for the spin-1 Bose-Hubbard model
T. Kimura
Abstract
In this study, we perform a strong-coupling expansion up to third order of the hopping parameter $t$ for the spin-1 Bose-Hubbard model with antiferromagnetic interaction. As expected from previous studies, the Mott-insulator phase is considerably more stable against the superfluid phase when filling with an even number of bosons than when filling with an odd number of bosons. The phase-boundary curves are consistent with the perturbative mean-field theory in the limit of infinite dimensions. The critical value of the hopping parameter ${t}_{\mathrm{C}}$ at the peak of the Mott lobe depends on the antiferromagnetic interaction. This result indicates the reliability of the strong-coupling expansion when ${U}_{2}$ possesses large (intermediate) values for Mott lobe with an even (odd) number of bosons. Moreover, in order to improve our results, we apply a few extrapolation methods up to infinite order in $t$. The fitting results of the phase-boundary curves agree better with those of the perturbative mean-field approximation. In addition, the linear fit error of ${t}_{\mathrm{C}}$ is very small for the strong antiferromagnetic interaction.