790 research outputs found
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
Hyperuniform long-range correlations are a signature of disordered jammed hard-particle packings
We show that quasi-long-range (QLR) pair correlations that decay
asymptotically with scaling in -dimensional Euclidean space
, trademarks of certain quantum systems and cosmological
structures, are a universal signature of maximally random jammed (MRJ)
hard-particle packings. We introduce a novel hyperuniformity descriptor in MRJ
packings by studying local-volume-fraction fluctuations and show that
infinite-wavelength fluctuations vanish even for packings with size- and
shape-distributions. Special void statistics induce hyperuniformity and QLR
pair correlations.Comment: 10 pages, 3 figures; changes to figures and text based on review
process; accepted for publication at Phys. Rev. Let
Solitonic Phase in Manganites
Whenever a symmetry in the ground state of a system is broken, topological
defects will exist. These defects are essential for understanding phase
transitions in low dimensional systems[1]. Excitingly in some unique condensed
matter systems the defects are also the low energy electric charge excitations.
This is the case of skyrmions in quantum Hall ferromagnets[2] and solitons in
polymers[3]. Orbital order present in several transitions metal compounds[4-6]
could give rise to topological defects. Here we argue that the topological
defects in orbital ordered half doped manganites are orbital solitons.
Surprisingly, these solitons carry a fractional charge of e/2, and
whenever extra charge is added to the system an array of solitons is formed and
an incommensurate solitonic phase occurs. The striking experimental asymmetry
in the phase diagram as electrons or holes are added to half doped
manganites[7-12], is explained by the energy difference between positive and
negative charged solitons. Contrary to existent models that explain coexistence
between phases in manganites as an extrinsic effect[13-14], the presence of
inhomogeneities is naturally explained by the existence of solitonic phases.
The occurrence and relevance of orbital solitons might be a general phenomena
in strongly correlated systems.Comment: 10 pages, 5 figures include
Phase diagram for Coulomb-frustrated phase separation in systems with negative short-range compressibility
Using numerical techniques and asymptotic expansions we obtain the phase
diagram of a paradigmatic model of Coulomb frustrated phase separation in
systems with negative short-range compressibility. The transition from the
homogeneous phase to the inhomogeneous phase is generically first order in
isotropic three-dimensional systems except for a critical point. Close to the
critical point, inhomogeneities are predicted to form a BCC lattice with
subsequent transitions to a triangular lattice of rods and a layered structure.
Inclusion of a strong anisotropy allows for second- and first-order transition
lines joined by a tricritical point.Comment: 4 pages, 3 figures. Improved figures and presentatio
Nonequilibrium Phase Transitions and a Nonequilibrium Critical Point from Anti-de Sitter Space and Conformal Field Theory Correspondence
We find novel phase transitions and critical phenomena that occur only
outside the linear-response regime of current-driven nonequilibrium states. We
consider the strongly-interacting (3+1)-dimensional N=4 large-Nc SU(Nc)
supersymmetric Yang-Mills theory with a single flavor of fundamental N=2
hypermultiplet as a microscopic theory. We compute its nonlinear non-ballistic
quark-charge conductivity by using the AdS/CFT correspondence. We find that the
system exhibits a novel nonequilibrium first-order phase transition where the
conductivity jumps and the sign of the differential conductivity flips at
finite current density. A nonequilibrium critical point is discovered at the
end point of the first-order regime. We propose a nonequilibrium steady-state
analogue of thermodynamic potential in terms of the gravity-dual theory in
order to define the transition point. Nonequilibrium analogues of critical
exponents are proposed as well. The critical behavior of the conductivity is
numerically confirmed on the basis of these proposals. The present work
provides a new example of nonequilibrium phase transitions and nonequilibrium
critical points.Comment: 5 pages, 2 figures; v2: slightly short version is published in PRL.
The title is changed in the PRL forma
Nonaffine Correlations in Random Elastic Media
Materials characterized by spatially homogeneous elastic moduli undergo
affine distortions when subjected to external stress at their boundaries, i.e.,
their displacements \uv (\xv) from a uniform reference state grow linearly
with position \xv, and their strains are spatially constant. Many materials,
including all macroscopically isotropic amorphous ones, have elastic moduli
that vary randomly with position, and they necessarily undergo nonaffine
distortions in response to external stress. We study general aspects of
nonaffine response and correlation using analytic calculations and numerical
simulations. We define nonaffine displacements \uv' (\xv) as the difference
between \uv (\xv) and affine displacements, and we investigate the
nonaffinity correlation function
and related functions. We introduce four model random systems with random
elastic moduli induced by locally random spring constants, by random
coordination number, by random stress, or by any combination of these. We show
analytically and numerically that scales as A |\xv|^{-(d-2)}
where the amplitude is proportional to the variance of local elastic moduli
regardless of the origin of their randomness. We show that the driving force
for nonaffine displacements is a spatial derivative of the random elastic
constant tensor times the constant affine strain. Random stress by itself does
not drive nonaffine response, though the randomness in elastic moduli it may
generate does. We study models with both short and long-range correlations in
random elastic moduli.Comment: 22 Pages, 18 figures, RevTeX
Numerical simulations of two dimensional magnetic domain patterns
I show that a model for the interaction of magnetic domains that includes a
short range ferromagnetic and a long range dipolar anti-ferromagnetic
interaction reproduces very well many characteristic features of
two-dimensional magnetic domain patterns. In particular bubble and stripe
phases are obtained, along with polygonal and labyrinthine morphologies. In
addition, two puzzling phenomena, namely the so called `memory effect' and the
`topological melting' observed experimentally are also qualitatively described.
Very similar phenomenology is found in the case in which the model is changed
to be represented by the Swift-Hohenberg equation driven by an external
orienting field.Comment: 8 pages, 8 figures. Version to appear in Phys. Rev.
Screening effects in Coulomb frustrated phase separation
We solve a model of phase separation among two competing phases frustrated by
the long-range Coulomb interaction in two and three dimensions (2D/3D) taking
into account finite compressibility effects. In the limit of strong frustration
in 2D, we recover the results of R. Jamei, S. Kivelson, and B. Spivak, Phys.
Rev. Lett. 94, 056805 (2005) and the system always breaks into domains in a
narrow range of densities, no matter how big is the frustration. For weak
frustration in 2D and for arbitrary frustration in 3D the finite
compressibility of the phases is shown to play a fundamental role. Our results
clarify the different role of screening in 2D and 3D systems. We discuss the
thermodynamic stability of the system near the transition to the phase
separated state and the possibility to observe it in real systems.Comment: 8 pages, 8 figure
Hyperuniformity, quasi-long-range correlations, and void-space constraints in maximally random jammed particle packings. I. Polydisperse spheres
Hyperuniform many-particle distributions possess a local number variance that
grows more slowly than the volume of an observation window, implying that the
local density is effectively homogeneous beyond a few characteristic length
scales. Previous work on maximally random strictly jammed sphere packings in
three dimensions has shown that these systems are hyperuniform and possess
unusual quasi-long-range pair correlations, resulting in anomalous logarithmic
growth in the number variance. However, recent work on maximally random jammed
sphere packings with a size distribution has suggested that such
quasi-long-range correlations and hyperuniformity are not universal among
jammed hard-particle systems. In this paper we show that such systems are
indeed hyperuniform with signature quasi-long-range correlations by
characterizing the more general local-volume-fraction fluctuations. We argue
that the regularity of the void space induced by the constraints of saturation
and strict jamming overcomes the local inhomogeneity of the disk centers to
induce hyperuniformity in the medium with a linear small-wavenumber nonanalytic
behavior in the spectral density, resulting in quasi-long-range spatial
correlations. A numerical and analytical analysis of the pore-size distribution
for a binary MRJ system in addition to a local characterization of the
n-particle loops governing the void space surrounding the inclusions is
presented in support of our argument. This paper is the first part of a series
of two papers considering the relationships among hyperuniformity, jamming, and
regularity of the void space in hard-particle packings.Comment: 40 pages, 15 figure
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