44 research outputs found
Quantum Phases of Ultracold Bosonic Atoms in a One Dimensional Optical Superlattice
We analyze various quantum phases of ultracold bosonic atoms in a periodic
one dimensional optical superlattice. Our studies have been performed using the
finite size density matrix renormalization group (FS-DMRG) method in the
framework of the Bose-Hubbard model. Calculations have been carried out for a
wide range of densities and the energy shifts due to the superlattice
potential. At commensurate fillings, we find the Mott insulator and the
superfluid phases as well as Mott insulators induced by the superlattice. At a
particular incommensurate density, the system is found to be in the superfluid
phase coexisting with density oscillations for a certain range of parameters of
the system.Comment: 7 pages, 11 figure
Hardcore bosons in a zig-zag optical superlattice
We study a system of hard-core bosons at half-filling in a one-dimensional
optical superlattice. The bosons are allowed to hop to nearest and next-nearest
neighbor sites producing a zig-zag geometry and we obtain the ground state
phase diagram as a function of microscopic parameters using the finite-size
density matrix renormalization group (FS-DMRG) method. Depending on the sign of
the next-nearest neighbor hopping and the strength of the superlattice
potential the system exhibits three different phases, namely the bond-order
(BO) solid, the superlattice induced Mott insulator (SLMI) and the superfluid
(SF) phase. When the signs of both hopping amplitudes are the same (the
"unfrustrated" case), the system undergoes a transition from the SF to the SLMI
at a non-zero value of the superlattice potential. On the other hand, when the
two amplitudes differ in sign (the "frustrated" case), the SF is unstable to
switching on a superlattice potential and also exists only up to a finite value
of the next nearest neighbor hopping. This part of the phase diagram is
dominated by the BO phase which breaks translation symmetry spontaneously even
in the absence of the superlattice potential and can thus be characterized by a
bond order parameter. The transition from BO to SLMI appears to be first order.Comment: 6 pages, 11 figure
Mean field analysis of quantum phase transitions in a periodic optical superlattice
In this paper we analyze the various phases exhibited by a system of
ultracold bosons in a periodic optical superlattice using the mean field
decoupling approximation. We investigate for a wide range of commensurate and
incommensurate densities. We find the gapless superfluid phase, the gapped Mott
insulator phase, and gapped insulator phases with distinct density wave orders.Comment: 6 pages, 7 figures, 4 table
Bose Hubbard Model in a Strong Effective Magnetic Field: Emergence of a Chiral Mott Insulator Ground State
Motivated by experiments on Josephson junction arrays, and cold atoms in an
optical lattice in a synthetic magnetic field, we study the "fully frustrated"
Bose-Hubbard (FFBH) model with half a magnetic flux quantum per plaquette. We
obtain the phase diagram of this model on a two-leg ladder at integer filling
via the density matrix renormalization group approach, complemented by Monte
Carlo simulations on an effective classical XY model. The ground state at
intermediate correlations is consistently shown to be a chiral Mott insulator
(CMI) with a gap to all excitations and staggered loop currents which
spontaneously break time reversal symmetry. We characterize the CMI state as a
vortex supersolid or an indirect exciton condensate, and discuss various
experimental implications.Comment: 4 pages, 4 figs, Significantly revised version, to appear in
PRA-Rapi