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arXiv:cond-mat/0312018 · Physical Review Letters

Phase Separation in the Two-Dimensional Bosonic Hubbard Model with Ring Exchange

V. G. Rousseau, G. G. Batrouni, Richard T. Scalettar

Published Sep 9, 2004• 15 citations
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Abstract

We show that soft-core bosons in two dimensions with a ring exchange term exhibit a tendency for phase separation. This observation suggests that the thermodynamic stability of normal Bose liquid phases driven by ring exchange should be carefully examined.
DOI
10.1103/physrevlett.93.110404

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We present quantum Monte Carlo simulations of the soft-core Bosonic Hubbard model with a ring exchange term KKK. For values of KKK which exceed roughly half the on-site repulsion UUU, the density is a nonmonotonic function of the chemical potential, indicating that the system has a tendency to phase separate. This behavior is confirmed by an examination of the density-density structure factor at small momenta and real-space images of the boson configurations. Adding a near-neighbor repulsion can compete with phase separation, but still does not give rise to a stable normal Bose liquid.
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Ring-exchange interactions have been proposed as a possible mechanism for a Bose-liquid phase at zero temperature, a phase that is compressible with no superfluidity. Using the stochastic Green function algorithm (SGF), we study the effect of these interactions for bosons on a two-dimensional triangular lattice. We show that the supersolid phase that is known to exist in the ground state for a wide range of densities is rapidly destroyed as the ring-exchange interactions are turned on. We establish the ground-state phase diagram of the system, which is characterized by the absence of the expected Bose-liquid phase.