6 research outputs found
The Bose-Hubbard model on a triangular lattice with diamond ring-exchange
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.Comment: 6 pages, 10 figure
Using off-diagonal confinement as a cooling method
In a recent letter [Phys. Rev. Lett. 104, 167201 (2010)] we proposed a new
confining method for ultracold atoms on optical lattices, based on off-diagonal
confinement (ODC). This method was shown to have distinct advantages over the
conventional diagonal confinement (DC) that makes use of a trapping potential,
including the existence of pure Mott phases and highly populated condensates.
In this paper we show that the ODC method can also lead to temperatures that
are smaller than with the conventional DC method, depending on the control
parameters. We determine these parameters using exact diagonalizations for the
hard-core case, then we extend our results to the soft-core case by performing
quantum Monte Carlo (QMC) simulations for both DC and ODC systems at fixed
temperatures, and analysing the corresponding entropies. We also propose a
method for measuring the entropy in QMC simulations.Comment: 6 pages, 6 figure
Local Density of the Bose Glass Phase
We study the Bose-Hubbard model in the presence of on-site disorder in the
canonical ensemble and conclude that the local density of the Bose glass phase
behaves differently at incommensurate filling than it does at commensurate one.
Scaling of the superfluid density at incommensurate filling of and
on-site interaction predicts a superfluid-Bose glass transition at
disorder strength of . At this filling the local density
distribution shows skew behavior with increasing disorder strength.
Multifractal analysis also suggests a multifractal behavior resembling that of
the Anderson localization. Percolation analysis points to a phase transition of
percolating non-integer filled sites around the same value of disorder. Our
findings support the scenario of percolating superfluid clusters enhancing
Anderson localization near the superfluid-Bose glass transition. On the other
hand, the behavior of the commensurate filled system is rather different. Close
to the tip of the Mott lobe () we find a Mott insulator-Bose
glass transition at disorder strength of . An analysis of
the local density distribution shows Gaussian like behavior for a wide range of
disorders above and below the transition.Comment: 12 pages, 14 figure