Quantum Phase Transitions in a Dimerized Bose-Hubbard Model: A DMRG Study

We investigate the phase diagram of a dimerized Bose-Hubbard model, using density matrix renormalization group technique. We find a new phase, which is the coexistence of superfluid and bond-wave phases, due to the effect of dimerization. Experimentally dimerization in optical lattice can be realized by using two counter propagating laser beams of different wavelengths. Apart from the conventional superfluid to Mott insulator transition, we find a new quantum phase transition: from superfluid-bond-wave to Mott insulator-bond wave phase. Our study suggests a rich phase diagram which can be easily probed. Introduction. – Over the last decade, there have been a large number of interesting theoretical predictions on the rich physics of strongly correlated optical lattice systems [1–3]. The spectacular experiment by Greiner et al. [4] has opened a new frontier, as it convincingly demonstrates that at low temperature, the cold atoms trapped in an optical lattice undergo a quantum phase transition from the delocalized superfluid (SF) state to the localized Mott insulator (MI) state. The unprecedented control in experiment over the theoretical parameters provides a good opportunity to study the various competing phases in this class of lattice systems. The theory of the underlying quantum phase transition of strongly interacting bosons confined in an optical lattice is described by the well-known Bose-Hubbard (BH) model [5]. The BH Hamiltonian is given by