10,756 research outputs found
Haldane charge conjecture in one-dimensional multicomponent fermionic cold atoms
A Haldane conjecture is revealed for spin-singlet charge modes in
2N-component fermionic cold atoms loaded into a one-dimensional optical
lattice. By means of a low-energy approach and DMRG calculations, we show the
emergence of gapless and gapped phases depending on the parity of for
attractive interactions at half-filling. The analogue of the Haldane phase of
the spin-1 Heisenberg chain is stabilized for N=2 with non-local string charge
correlation, and pseudo-spin 1/2 edge states. At the heart of this even-odd
behavior is the existence of a spin-singlet pseudo-spin operator which
governs the low-energy properties of the model for attractive interactions and
gives rise to the Haldane physics.Comment: 4 pages, 4 figure
Competing orders in one-dimensional half-filled multicomponent fermionic cold atoms: The Haldane-charge conjecture
We investigate the nature of the Mott-insulating phases of half-filled
2N-component fermionic cold atoms loaded into a one-dimensional optical
lattice. By means of conformal field theory techniques and large-scale DMRG
calculations, we show that the phase diagram strongly depends on the parity of
. First, we single out charged, spin-singlet, degrees of freedom, that carry
a pseudo-spin allowing to formulate a Haldane conjecture: for
attractive interactions, we establish the emergence of Haldane insulating
phases when is even, whereas a metallic behavior is found when is odd.
We point out that the cases do \emph{not} have the generic properties
of each family. The metallic phase for odd and larger than 1 has a
quasi-long range singlet pairing ordering with an interesting edge-state
structure. Moreover, the properties of the Haldane insulating phases with even
further depend on the parity of N/2. In this respect, within the low-energy
approach, we argue that the Haldane phases with N/2 even are not topologically
protected but equivalent to a topologically trivial insulating phase and thus
confirm the recent conjecture put forward by Pollmann {\it et al.} [Pollmann
{\it et al.}, arXiv:0909.4059 (2009)].Comment: 25 pages, 20 figure
Internal avalanches in models of granular media
We study the phenomenon of internal avalanching within the context of
recently introduced lattice models of granular media. The avalanche is produced
by pulling out a grain at the base of the packing and studying how many grains
have to rearrange before the packing is once more stable. We find that the
avalanches are long-ranged, decaying as a power-law. We study the distriution
of avalanches as a function of the density of the packing and find that the
avalanche distribution is a very sensitive structural probe of the system.Comment: 12 pages including 9 eps figures, LaTeX. To appear in Fractal
Slow quench dynamics of Mott-insulating regions in a trapped Bose gas
We investigate the dynamics of Mott-insulating regions of a trapped bosonic
gas as the interaction strength is changed linearly with time. The bosonic gas
considered is loaded into an optical lattice and confined to a parabolic
trapping potential. Two situations are addressed: the formation of Mott domains
in a superfluid gas as the interaction is increased, and their melting as the
interaction strength is lowered. In the first case, depending on the local
filling, Mott-insulating barriers can develop and hinder the density and energy
transport throughout the system. In the second case, the density and local
energy adjust rapidly whereas long range correlations require longer time to
settle. For both cases, we consider the time evolution of various observables:
the local density and energy, and their respective currents, the local
compressibility, the local excess energy, the heat and single particle
correlators. The evolution of these observables is obtained using the
time-dependent density-matrix renormalization group technique and comparisons
with time-evolutions done within the Gutzwiller approximation are provided.Comment: 15 pages, 13 figure
Equilibrium onions?
We demonstrate the possibility of a stable equilibrium multi-lamellar ("onion") phase in pure lamellar systems (no excess solvent) due to a sufficiently negative Gaussian curvature modulus. The onion phase is stabilized by non-linear elastic moduli coupled to a polydisperse size distribution (Apollonian packing) to allow space-filling without appreciable elastic distortion. This model is compared to experiments on copolymer-decorated lamellar surfactant systems, with reasonable qualitative agreement
Large scale numerical simulations of "ultrametric" long-range depinning
The depinning of an elastic line interacting with a quenched disorder is
studied for long range interactions, applicable to crack propagation or
wetting. An ultrametric distance is introduced instead of the Euclidean
distance, allowing for a drastic reduction of the numerical complexity of the
problem. Based on large scale simulations, two to three orders of magnitude
larger than previously considered, we obtain a very precise determination of
critical exponents which are shown to be indistinguishable from their Euclidean
metric counterparts. Moreover the scaling functions are shown to be unchanged.
The choice of an ultrametric distance thus does not affect the universality
class of the depinning transition and opens the way to an analytic real space
renormalization group approach.Comment: submitted to Phys. Rev.
Elastic wave propagation in confined granular systems
We present numerical simulations of acoustic wave propagation in confined
granular systems consisting of particles interacting with the three-dimensional
Hertz-Mindlin force law. The response to a short mechanical excitation on one
side of the system is found to be a propagating coherent wavefront followed by
random oscillations made of multiply scattered waves. We find that the coherent
wavefront is insensitive to details of the packing: force chains do not play an
important role in determining this wavefront. The coherent wave propagates
linearly in time, and its amplitude and width depend as a power law on
distance, while its velocity is roughly compatible with the predictions of
macroscopic elasticity. As there is at present no theory for the broadening and
decay of the coherent wave, we numerically and analytically study
pulse-propagation in a one-dimensional chain of identical elastic balls. The
results for the broadening and decay exponents of this system differ
significantly from those of the random packings. In all our simulations, the
speed of the coherent wavefront scales with pressure as ; we compare
this result with experimental data on various granular systems where deviations
from the behavior are seen. We briefly discuss the eigenmodes of the
system and effects of damping are investigated as well.Comment: 20 pages, 12 figures; changes throughout text, especially Section V.
- …