Quantum phase transition in a two-dimensional system of dipoles
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The ground-state phase diagram of a two-dimensional Bose system with dipole-dipole interactions is studied by means of quantum Monte Carlo technique. Our calculation predicts a quantum phase transition from gas to solid phase when the density increases. In the gas phase the condensate fraction is calculated as a function of the density. Using Feynman approximation, the collective excitation branch is studied and appearance of a roton minimum is observed. Results of the static structure factor at both sides of the gas-solid phase are also presented. The Lindeman ratio at the transition point comes to be $γ= 0.230(6)$. The condensate fraction in the gas phase is estimated as a function of the density.
4 figures v.3 One citation added, updated Fig.4. Minor changes following referee's and editor's comments
4 figures v.3 One citation added, updated Fig.4. Minor changes following referee's and editor's comments