Article

Strong-coupling expansion for the two-species Bose-Hubbard model

Physical Review A (Impact Factor: 2.81). 12/2009; 82(3). DOI: 10.1103/PHYSREVA.82.033630
Source: arXiv

ABSTRACT

To analyze the ground-state phase diagram of Bose-Bose mixtures loaded into $d$-dimensional hypercubic optical lattices, we perform a strong-coupling power-series expansion in the kinetic energy term (plus a scaling analysis) for the two-species Bose-Hubbard model with onsite boson-boson interactions. We consider both repulsive and attractive interspecies interaction, and obtain an analytical expression for the phase boundary between the incompressible Mott insulator and the compressible superfluid phase up to third order in the hoppings. In particular, we find a re-entrant quantum phase transition from paired superfluid (superfluidity of composite bosons, i.e. Bose-Bose pairs) to Mott insulator and again to a paired superfluid in all one, two and three dimensions, when the interspecies interaction is sufficiently large and attractive. We hope that some of our results could be tested with ultracold atomic systems. Comment: 8 pages, 4 figures, and 2 tables (published version)

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    • "In the past decade, quantum phase transitions of Bose-Bose, Bose-Fermi and Fermi-Fermi mixtures in optical lattices have attracted considerable attention both experimentally and theoretically [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]. Nonetheless, the physics of mixtures is still not completely understood. "
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    ABSTRACT: We perform a numeric study (Worm algorithm Monte Carlo simulations) of ultracold two-component bosons in two-dimensional optical lattices. We study how the Mott insulator to superfluid transition is affected by the presence of a second superfluid bosonic species. We find that, at fixed interspecies interaction, the upper and lower boundaries of the Mott lobe are differently modified. The lower boundary is strongly renormalized even for relatively low filling factor of the second component and moderate (interspecies) interaction. The upper boundary, instead, is affected only for large enough filling of the second component. Whereas boundaries are renormalized we find evidence of polaron-like excitations. Our results are of interest for current experimental setups.
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