1,997 research outputs found
On the Melting of Bosonic Stripes
We use quantum Monte Carlo simulations to determine the finite temperature
phase diagram and to investigate the thermal and quantum melting of stripe
phases in a two-dimensional hard-core boson model. At half filling and low
temperatures the stripes melt at a first order transition. In the doped system,
the melting transitions of the smectic phase at high temperatures and the
superfluid smectic (supersolid) phase at low temperatures are either very
weakly first order, or of second order with no clear indications for an
intermediate nematic phase.Comment: 4 pages, 5 figure
Magnetization plateaux and jumps in a class of frustrated ladders: A simple route to a complex behaviour
We study the occurrence of plateaux and jumps in the magnetization curves of
a class of frustrated ladders for which the Hamiltonian can be written in terms
of the total spin of a rung. We argue on the basis of exact diagonalization of
finite clusters that the ground state energy as a function of magnetization can
be obtained as the minimum - with Maxwell constructions if necessary - of the
energies of a small set of spin chains with mixed spins. This allows us to
predict with very elementary methods the existence of plateaux and jumps in the
magnetization curves in a large parameter range, and to provide very accurate
estimates of these magnetization curves from exact or DMRG results for the
relevant spin chains.Comment: 14 pages REVTeX, 7 PostScript figures included using psfig.sty; this
is the final version to appear in Eur. Phys. J B; some references added and a
few other minor change
Ferromagnetism of a Repulsive Atomic Fermi Gas in an Optical Lattice: a Quantum Monte Carlo Study
Using continuous-space quantum Monte Carlo methods we investigate the
zero-temperature ferromagnetic behavior of a two-component repulsive Fermi gas
under the influence of periodic potentials that describe the effect of a
simple-cubic optical lattice. Simulations are performed with balanced and with
imbalanced components, including the case of a single impurity immersed in a
polarized Fermi sea (repulsive polaron). For an intermediate density below half
filling, we locate the transitions between the paramagnetic, and the partially
and the fully ferromagnetic phases. As the intensity of the optical lattice
increases, the ferromagnetic instability takes place at weaker interactions,
indicating a possible route to observe ferromagnetism in experiments performed
with ultracold atoms. We compare our findings with previous predictions based
on the standard computational method used in material science, namely density
functional theory, and with results based on tight-binding models.Comment: Published version with Supplemental Material. Added comparison with
Hubbard model result
Quantum Phase Transitions in Coupled Dimer Compounds
We study the critical properties in cubic systems of antiferromagnetically
coupled spin dimers near magnetic-field induced quantum phase transitions. The
quantum critical points in the zero-temperature phase diagrams are determined
from quantum Monte Carlo simulations. Furthermore, scaling properties of the
uniform magnetization and the staggered transverse magnetization across the
quantum phase transition in magnetic fields are calculated. The critical
exponents are derived from Ginzburg-Landau theory. We find excellent agreement
between the quantum Monte Carlo simulations and the analytical results.Comment: 7 pages, 9 eps-figure
Competing states in the t-J model: uniform d-wave state versus stripe state
Variational studies of the t-J model on the square lattice based on infinite
projected-entangled pair states (iPEPS) confirm an extremely close competition
between a uniform d-wave superconducting state and different stripe states. The
site-centered stripe with an in-phase d-wave order has an equal or only
slightly lower energy than the stripe with anti-phase d-wave order. The optimal
stripe filling is not constant but increases with J/t. A nematic anisotropy
reduces the pairing amplitude and the energies of stripe phases are lowered
relative to the uniform state with increasing nematicity.Comment: 6 pages, 4 figures, 4 pages of supplemental materia
A continuous-time solver for quantum impurity models
We present a new continuous time solver for quantum impurity models such as
those relevant to dynamical mean field theory. It is based on a stochastic
sampling of a perturbation expansion in the impurity-bath hybridization
parameter. Comparisons to quantum Monte Carlo and exact diagonalization
calculations confirm the accuracy of the new approach, which allows very
efficient simulations even at low temperatures and for strong interactions. As
examples of the power of the method we present results for the temperature
dependence of the kinetic energy and the free energy, enabling an accurate
location of the temperature-driven metal-insulator transition.Comment: Published versio
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