1,663 research outputs found
Quantifying hidden order out of equilibrium
While the equilibrium properties, states, and phase transitions of
interacting systems are well described by statistical mechanics, the lack of
suitable state parameters has hindered the understanding of non-equilibrium
phenomena in diverse settings, from glasses to driven systems to biology. The
length of a losslessly compressed data file is a direct measure of its
information content: The more ordered the data is, the lower its information
content and the shorter the length of its encoding can be made. Here, we
describe how data compression enables the quantification of order in
non-equilibrium and equilibrium many-body systems, both discrete and
continuous, even when the underlying form of order is unknown. We consider
absorbing state models on and off-lattice, as well as a system of active
Brownian particles undergoing motility-induced phase separation. The technique
reliably identifies non-equilibrium phase transitions, determines their
character, quantitatively predicts certain critical exponents without prior
knowledge of the order parameters, and reveals previously unknown ordering
phenomena. This technique should provide a quantitative measure of organization
in condensed matter and other systems exhibiting collective phase transitions
in and out of equilibrium
Bound States of Conical Singularities in Graphene-Based Topological Insulators
We investigate the electronic structure induced by wedge-disclinations
(conical singularities) in a honeycomb lattice model realizing Chern numbers
. We establish a correspondence between the bound state of (i) an
isolated -flux, (ii) an isolated pentagon or heptagon
defect with an external flux of magnitude through
the center and (iii) an isolated square or octagon defect without external
flux, where is the flux quantum. Due to the above correspondence,
the existence of isolated electronic states bound to the disclinations is
robust against various perturbations. These results are also generalized to
graphene-based time-reversal invariant topological insulators.Comment: 5+4 pages, 4+3 figures, revised introduction and Fig.
Tailoring of phononic band structures in colloidal crystals
We report an experimental study of the elastic properties of a
two-dimensional (2D) colloidal crystal subjected to light-induced substrate
potentials. In agreement with recent theoretical predictions [H.H. von
Gruenberg and J. Baumgartl, Phys. Rev. E 75, 051406 (2007)] the phonon band
structure of such systems can be tuned depending on the symmetry and depth of
the substrate potential. Calculations with binary crystals suggest that
phononic band engineering can be also performed by variations of the pair
potential and thus opens novel perspectives for the fabrication of phononic
crystals with band gaps tunable by external fields.Comment: 4 pages, 4 figures, to appear in Physical Review Letter
Crystallization in Glassy Suspensions of Hard Ellipsoids
We have carried out computer simulations of overcompressed suspensions of
hard monodisperse ellipsoids and observed their crystallization dynamics. The
system was compressed very rapidly in order to reach the regime of slow,
glass-like dynamics. We find that, although particle dynamics become
sub-diffusive and the intermediate scattering function clearly develops a
shoulder, crystallization proceeds via the usual scenario: nucleation and
growth for small supersaturations, spinodal decomposition for large
supersaturations.
In particular, we compared the mobility of the particles in the regions where
crystallization set in with the mobility in the rest of the system. We did not
find any signature in the dynamics of the melt that pointed towards the
imminent crystallization events
Inducing topological order in a honeycomb lattice
We explore the possibility of inducing a topological insulator phase in a
honeycomb lattice lacking spin-orbit interaction using a metallic (or Fermi
gas) environment. The lattice and the metallic environment interact through a
density-density interaction without particle tunneling, and integrating out the
metallic environment produces a honeycomb sheet with in-plane oscillating
long-ranged interactions. We find the ground state of the interacting system in
a variational mean-field method and show that the Fermi wave vector, kF, of the
metal determines which phase occurs in the honeycomb lattice sheet. This is
analogous to the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism in which the
metal's kF determines the interaction profile as a function of the distance.
Tuning kF and the interaction strength may lead to a variety of ordered phases,
including a topological insulator and anomalous quantum-hall states with
complex next-nearest-neighbor hopping, as in the Haldane and the Kane-Mele
model. We estimate the required range of parameters needed for the topological
state and find that the Fermi vector of the metallic gate should be of the
order of 3Pi/8a (with a being the graphene lattice constant). The net coupling
between the layers, which includes screening in the metal, should be of the
order of the honeycomb lattice bandwidth. This configuration should be most
easily realized in a cold-atoms setting with two interacting Fermionic species.Comment: 7 pages; 2 figures; Version 2 - added references; added an appendix
about screenin
Spinodal decomposition during the hadronization stage at RHIC?
The expansion of strongly interacting matter formed in high-energy nuclear
collisions drives the system through the region of phase coexistence. The
present study examines the associated spinodal instability and finds that the
degree of amplification may be sufficient to raise the prospect of using the
spinodal pattern formation as a diagnostic tool for probing the hadronization
phase transition.Comment: 4 pages, 4 eps figure
A Note on Charged Black Holes in AdS space and the Dual Gauge Theories
We study the thermodynamics and the phase structures of Reissner-Nordstrom
and Born-Infeld black holes in AdS space by constructing ``off-shell'' free
energies using thermodynamic quantities derived directly from the action. We
then use these results to propose ``off-shell'' effective potentials for the
respective boundary gauge theories. The saddle points of the potentials
describe all the equilibrium phases of the gauge theories.Comment: LaTeX, 21+1 pages, 7 figure
Heat wave propagation in a nonlinear chain
We investigate the propagation of temperature perturbations in an array of
coupled nonlinear oscillators at finite temperature. We evaluate the response
function at equilibrium and show how the memory effects affect the diffusion
properties. A comparison with nonequilibrium simulations reveals that the
telegraph equation provides a reliable interpretative paradigm for describing
quantitatively the propagation of a heat pulse at the macroscopic level. The
results could be of help in understanding and modeling energy transport in
individual nanotubes.Comment: Revised version, 1 fig. adde
Dirty, Skewed, and Backwards: The Smectic - Phase Transition in Aerogel
We study the smectic AC transition in anisotropic and uniaxial disordered
environments, e.g., aerogel with an external field. We find very strange
behavior of translational correlations: the low-temperature, lower-symmetry
Smectic C phase is itless translationally ordered than the it high-temperature,
higher-symmetry Smectic A phase, with short-ranged and algebraic translational
correlations, respectively. Specifically, the A and C phase belong to the
quasi-long-ranged translationally ordered " XY Bragg glass '' and short-ranged
translationally ordered " m=1 Bragg glass '' phase, respectively. The AC phase
transition itself belongs to a new universality class, whose fixed points and
exponents we find in a d=5-epsilon expansion
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