6 research outputs found
One-dimensional phase transitions in a two-dimensional optical lattice
A phase transition for bosonic atoms in a two-dimensional anisotropic optical
lattice is considered. If the tunnelling rates in two directions are different,
the system can undergo a transition between a two-dimensional superfluid and a
one-dimensional Mott insulating array of strongly coupled tubes. The connection
to other lattice models is exploited in order to better understand the phase
transition. Critical properties are obtained using quantum Monte Carlo
calculations. These critical properties are related to correlation properties
of the bosons and a criterion for commensurate filling is established.Comment: 14 pages, 8 figure
Two-Dimensional Quantum XY Model with Ring Exchange and External Field
We present the zero-temperature phase diagram of a square lattice quantum
spin 1/2 XY model with four-site ring exchange in a uniform external magnetic
field. Using quantum Monte Carlo techniques, we identify various quantum phase
transitions between the XY-order, striped or valence bond solid, staggered Neel
antiferromagnet and fully polarized ground states of the model. We find no
evidence for a quantum spin liquid phase.Comment: 4 pages, 4 figure