9,698 research outputs found
Field Induced Supersolid Phase in Spin-One Heisenberg Models
We use quantum Monte Carlo methods to demonstrate that the quantum phase
diagram of the S=1 Heisenberg model with uniaxial anisotropy contains an
extended supersolid phase. We also show that this Hamiltonian is a particular
case of a more general and ubiquitous model that describes the low energy
spectrum of a class of {\it isotropic} and {\it frustrated} spin systems. This
crucial result provides the required guidance for finding experimental
realizations of a spin supersolid state.Comment: 4 pages, 4 figure
Non-equilibrium dynamics of the Bose-Hubbard model: A projection operator approach
We study the phase diagram and non-equilibrium dynamics, both subsequent to a
sudden quench of the hopping amplitude and during a ramp
with ramp time , of the Bose-Hubbard model at zero temperature using a
projection operator formalism which allows us to incorporate the effects of
quantum fluctuations beyond mean-field approximations in the strong coupling
regime. Our formalism yields a phase diagram which provides a near exact match
with quantum Monte Carlo results in three dimensions. We also compute the
residual energy , the superfluid order parameter , the equal-time
order parameter correlation function , and the wavefunction overlap
which yields the defect formation probability during non-equilibrium
dynamics of the model. We find that , , and do not exhibit the
expected universal scaling. We explain this absence of universality and show
that our results compare well with recent experiments.Comment: Replaced with the accepted version, added one figure. 4 pages, 4
figures, to appear in Phys. Rev. Let
The Semiclassical Limit for and Gauge Theory on the Torus
We prove that for and quantum gauge theory on a torus,
holonomy expectation values with respect to the Yang-Mills measure d\mu_T(\o)
=N_T^{-1}e^{-S_{YM}(\o)/T}[{\cal D}\o] converge, as , to
integrals with respect to a symplectic volume measure on the moduli
space of flat connections on the bundle. These moduli spaces and the symplectic
structures are described explicitly.Comment: 18 page
Modulus stabilization of generalized Randall Sundrum model with bulk scalar field
We study the stabilization of inter-brane spacing modulus of generalized
warped brane models with a nonzero brane cosmological constant. Employing
Goldberger-Wise stabilization prescription of brane world models with a bulk
scalar field, we show that the stabilized value of the modulus generally
depends on the value of the brane cosmological constant. Our result further
reveals that the stabilized modulus value corresponding to a vanishingly small
cosmological constant can only resolve the gauge hierarchy problem
simultaneously. This in turn vindicates the original Randall-Sundrum model
where the 3-brane cosmological constant was chosen to be zero.Comment: 12 Pages, 1 figure, Revtex, Version to appear in Euro. Phys. Let
A projection operator approach to the Bose-Hubbard model
We develop a projection operator formalism for studying both the zero
temperature equilibrium phase diagram and the non-equilibrium dynamics of the
Bose-Hubbard model. Our work, which constitutes an extension of Phys. Rev.
Lett. {\bf 106}, 095702 (2011), shows that the method provides an accurate
description of the equilibrium zero temperature phase diagram of the
Bose-Hubbard model for several lattices in two- and three-dimensions (2D and
3D). We show that the accuracy of this method increases with the coordination
number of the lattice and reaches to within 0.5% of quantum Monte Carlo
data for lattices with . We compute the excitation spectra of the bosons
using this method in the Mott and the superfluid phases and compare our results
with mean-field theory. We also show that the same method may be used to
analyze the non-equilibrium dynamics of the model both in the Mott phase and
near the superfluid-insulator quantum critical point where the hopping
amplitude and the on-site interaction satisfy . In
particular, we study the non-equilibrium dynamics of the model both subsequent
to a sudden quench of the hopping amplitude and during a ramp from to
characterized by a ramp time and exponent : . We compute the wavefunction overlap , the
residual energy , the superfluid order parameter , the equal-time
order parameter correlation function , and the defect formation
probability for the above-mentioned protocols and provide a comparison of
our results to their mean-field counterparts. We find that , , and do
not exhibit the expected universal scaling. We explain this absence of
universality and show that our results for linear ramps compare well with the
recent experimental observations.Comment: v2; new references and new sections adde
Single-file diffusion and kinetics of template assisted assembly of colloids
We report computer simulation studies of the kinetics of ordering of a two
dimensional system of particles on a template with a one dimensional periodic
pattern. In equilibrium one obtains a re-entrant liquid-solid-liquid phase
transition as the strength of the substrate potential is varied. We show that
domains of crystalline order grow as , with with a
possible cross-over to at late times. We argue that the
law originates from {\em single-file} motion and annihilation of defect pairs
of opposite topological charge along channels created by the template.Comment: 4 pages pdflatex 4 pdf figure
An anomalous magnetic phase transition at 10 K in Nd7Rh3
The compound, Nd7Rh3, crystallizing in Th7Fe3-type hexagonal structure, has
been shown recently by us to exhibit a signature of magnetic phase-coexistence
phenomenon below 10 K after a field cycling, uncharacteristic of stoichiometric
intermetallic compounds, bearing a relevance to the trends in the field of
electronic phase-separation. In order to characterize this compound further, we
have carried out dc magnetic susceptibility (chi), electrical resistivity,
magnetoresistance and heat-capacity measurements as a function temperature (T=
1.8 to 300 K). The results reveal that this compound exhibits another unusual
finding at the 10K-transition in the sense that the plot of chi(T) shows a
sharp increase in the field-cooled cycle, whereas the zero-field-cooled curve
shows a downturn below the transition. In addition, the sign of
magnetoresistance is negative and the magnitude is large over a wide
temperature range in the vicinity of magnetic ordering temperature, with a
sharp variation at 10 K. The results indicate that the transition below 10 K is
first-order in its character.Comment: Appeared in JPCM (Letters) 18 (2006) L40
Chemotactic predator-prey dynamics
A discrete chemotactic predator-prey model is proposed in which the prey
secrets a diffusing chemical which is sensed by the predator and vice versa.
Two dynamical states corresponding to catching and escaping are identified and
it is shown that steady hunting is unstable. For the escape process, the
predator-prey distance is diffusive for short times but exhibits a transient
subdiffusive behavior which scales as a power law with time and
ultimately crosses over to diffusion again. This allows to classify the
motility and dynamics of various predatory bacteria and phagocytes. In
particular, there is a distinct region in the parameter space where they prove
to be infallible predators.Comment: 4 pages, 4 figure
Spin Supersolid in Anisotropic Spin-One Heisenberg Chain
We consider an S=1 Heisenberg chain with strong exchange (Delta) and
single--ion uniaxial anisotropy (D) in a magnetic field (B) along the symmetry
axis. The low energy spectrum is described by an effective S=1/2 XXZ model that
acts on two different low energy sectors for a given window of fields. The
vacuum of each sector exhibits Ising-like antiferromagnetic ordering that
coexists with the finite spin stiffness obtained from the exact solution of the
effective XXZ model. In this way, we demonstrate the existence of a spin
supersolid phase. We also compute the full Delta-B quantum phase diagram by
means of a quantum Monte Carlo simulation.Comment: 4+ pages, 2 fig
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