32 research outputs found
Pair supersolid of the extended Bose-Hubbard model with atom-pair hopping on the triangular Lattice
We systematically study an extended Bose-Hubbard model with atom hopping and
atom-pair hopping in the presence of a three-body constraint on the triangular
lattice. By means of large-scale Quantum Monte Carlo simulations, the
ground-state phase diagram are studied. We find a continuous transition between
the atomic superfluid phase and the pair superfluid when the ratio of the
atomic hopping and the atom-pair hopping is adapted. We then focus on the
interplay among the atom-pair hopping, the on-site repulsion and the
nearest-neighbor repulsion. With on-site repulsion present, we observe first
order transitions between the Mott Insulators and pair superfluid driven by the
pair hopping. With the nearest-neighbor repulsion turning on, three typical
solid phases with 2/3, 1 and 4/3-filling emerge at small atom-pair hopping
region. A stable pair supersolid phase is found at small on-site repulsion.
This is due to the three-body constraint and the pair hopping, which
essentially make the model a quasi hardcore boson system. Thus the pair
supersolid state emerges basing on the order-by-disorder mechanism, by which
hardcore bosons avoid classical frustration on the triangular lattice. The
transition between the pair supersolid and the pair superfluid is first order,
except for the particle-hole symmetric point. We compare the results with those
obtained by means of mean-field analysis.Comment: 6 pages, 7 figure
Supersolid and pair correlations of the extended Jaynes-Cummings-Hubbard model on triangular lattices
We study the extended Jaynes-Cummings-Hubbard model on triangular cavity
lattices and zigzag ladders. By using density-matrix renormalization group
methods, we observe various types of solids with different density patterns and
find evidence for light supersolids, which exist in extended regions of the
phase diagram of the zigzag ladder. Furthermore, we observe strong pair
correlations in the supersolid phase due to the interplay between the atoms in
the cavities and atom-photon interaction. By means of cluster mean-field
simulations and a scaling of the cluster size extending our analysis to
two-dimensional triangular lattices, we present evidence for the emergence of a
light supersolid in this case also.Comment: 11 pages, 16 figure
Hardcore bosons on the dual of the bowtie lattice
We study the zero temperature phase diagram of hardcore bosons on the dual of
the bowtie lattice. Two types of striped diagonal long-range order (striped
order I and striped order II) are discussed. A state with type-II striped order
and superfluidity is found, even without nearest-neighbor repulsion. The
emergence of such a state is due to the inhomogeneity and the anisotropy of the
lattice structure. However, neither the translational symmetry nor the symmetry
between sublattices of the original lattice is broken. In this paper, we
restrict a 'solid state' of lattice bosons as a diagonal long-range ordered
state breaking either the translational symmetry of the original lattice or the
symmetry of different sublattices. We thus name such a phase a striped
superfluid phase (SSF). In the presence of a nearest-neighbor repulsion, we
find two striped charge density wave phases(SCDW I and II) with boson density
(with striped order I) and (with striped order II)
respectively, when the hopping amplitude is small compared with the repulsion.
The SCDW I state is a solid, in which the translational symmetry of the
original lattice is broken. We observe a rather special first-order phase
transition showing an interesting multi-loop hysteresis phenomenon between the
two SCDW phases when the hopping term is small enough. This can be accounted
for by the special degeneracy of the ground states near the classical limit.
The SSF re-appears outside the two SCDW phases. The transition between the SCDW
I and SSF phases is first order, while the transition between SCDW II and SSF
phases is continuous. We find that the superfluid stiffness is anisotropic in
the SSF states with and without repulsion. In the SSF with repulsion, the
superfluid stiffness is subject to different types of anisotropy in the region
near half filling and above 2/3-filling.Comment: 10 figure
Sublattice extraordinary-log phase and new special point of the antiferromagnetic Potts model
We study the surface criticality of a three-dimensional classical
antiferromagnetic Potts model, whose bulk critical behaviors belongs to the XY
model because of emergent O(2) symmetry. We find that the surface
antiferromagnetic next-nearest neighboring interactions can drive the
extraordinary-log phase to the ordinary phase, the transition between the two
phases belongs to the universality class of the well-known special transition
of the XY model. Further strengthening the surface next-nearest neighboring
interactions, the extraordinary-log phase reappears, but the main critical
behaviors are dominated on the sublattices of the model; the special point
between the ordinary phase and the sublattice extraordinary-log phase belongs
to a new universality class.Comment: 6 pages, 7 figure
Unsupervised machine learning for identifying phase transition using two-times clustering
In recent years, developing unsupervised machine learning for identifying
phase transition is a research direction. In this paper, we introduce a
two-times clustering method that can help select perfect configurations from a
set of degenerate samples and assign the configuration with labels in a manner
of unsupervised machine learning. These perfect configurations can then be used
to train a neural network to classify phases. The derivatives of the predicted
classification in the phase diagram, show peaks at the phase transition points.
The effectiveness of our method is tested for the Ising, Potts, and Blume-Capel
models. By using the ordered configuration from two-times clustering, our
method can provide a useful way to obtain phase diagrams.Comment: 8 pages, 7 figure
Effects of edge disorder in nano-scale antiferromagnetic clusters
We study the distribution of local magnetic susceptibilities in the
two-dimensional antiferromagnetic S=1/2 Heisenberg model on various random
clusters, in order to determine whether effects of edge disorder could be
detected in NMR experiments (through the line shape, as given by the
distribution of local Knight shifts). Although the effects depend strongly on
the nature of the edge and the cluster size, our results indicate that line
widths broader than the average shift should be expected even in clusters as
large as lattice spacing in diameter. Experimental
investigations of the NMR line width should give insights into the magnetic
structure of the edges.Comment: 4 pages, 4 figure