paper

Phase diagram and pair Tomonaga-Luttinger liquid in a Bose-Hubbard model with flat bands

arXiv:1309.6329 · doi:10.1103/PhysRevA.88.063613

Abstract

To explore superfluidity in flat-band systems, we consider a Bose-Hubbard model on a cross-linked ladder with flux, which has a flat band with a gap between the other band for noninteracting particles, where we study the effect of the on-site repulsion nonperturbatively. For low densities, we find exact degenerate ground states, each of which is a Wigner solid with nonoverlapping Wannier states on the flat band. At higher densities, the many-body system, when projected onto the lower flat band, can be mapped to a spin-chain model. This mapping enables us to reveal the existence of a Tomonaga-Luttinger liquid comprising it pairs of bosons. Interestingly, the high- and low- density regions have an overlap, where the two phases coexist.

6 pages, 4 figures

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