3,788 research outputs found
Localization of solitons: linear response of the mean-field ground state to weak external potentials
Two aspects of bright matter-wave solitons in weak external potentials are
discussed. First, we briefly review recent results on the Anderson localization
of an entire soliton in disordered potentials [Sacha et al. PRL 103, 210402
(2009)], as a paradigmatic showcase of genuine quantum dynamics beyond simple
perturbation theory. Second, we calculate the linear response of the mean-field
soliton shape to a weak, but otherwise arbitrary external potential, with a
detailed application to lattice potentials.Comment: Selected paper presented at the 2010 Spring Meeting of the Quantum
Optics and Photonics Section of the German Physical Society. V2: minor
changes, published versio
Toughening and asymmetry in peeling of heterogeneous adhesives
The effective adhesive properties of heterogeneous thin films are
characterized through a combined experimental and theoretical investigation. By
bridging scales, we show how variations of elastic or adhesive properties at
the microscale can significantly affect the effective peeling behavior of the
adhesive at the macroscale. Our study reveals three elementary mechanisms in
heterogeneous systems involving front propagation: (i) patterning the elastic
bending stiffness of the film produces fluctuations of the driving force
resulting in dramatically enhanced resistance to peeling; (ii) optimized
arrangements of pinning sites with large adhesion energy are shown to control
the effective system resistance, allowing the design of highly anisotropic and
asymmetric adhesives; (iii) heterogeneities of both types result in front
motion instabilities producing sudden energy releases that increase the overall
adhesion energy. These findings open potentially new avenues for the design of
thin films with improved adhesion properties, and motivate new investigation of
other phenomena involving front propagation.Comment: Physical Review Letters (2012)
Enhancement of the electromechanical response in ferroelectric ceramics by design
It is demonstrated based on continuum mechanics modeling and simulation that
it is possible to obtain polycrystalline ceramic ferroelectric materials which
beggars single crystals in electromechanical properties. The local
inhomogeneities at the ferroelectric domain-scale level due to spontaneous
polarization and the underlying anisotropy are taken into consideration in the
framework of mathematical homogenization of physical properties in
ferroelectric materials. The intrinsic randomness of the spatial distribution
of polarization is shown to be judiciously employed for the design of better
polycrystalline ferroelectrics. The noncollinear rotation of the net
polarization-vectors embedded in crystallites of the ceramic ferroelectrics is
demonstrated to play the key role in the enhancement of physical properties.Comment: 7 fugure
Three-dimensional localization of ultracold atoms in an optical disordered potential
We report a study of three-dimensional (3D) localization of ultracold atoms
suspended against gravity, and released in a 3D optical disordered potential
with short correlation lengths in all directions. We observe density profiles
composed of a steady localized part and a diffusive part. Our observations are
compatible with the self-consistent theory of Anderson localization, taking
into account the specific features of the experiment, and in particular the
broad energy distribution of the atoms placed in the disordered potential. The
localization we observe cannot be interpreted as trapping of particles with
energy below the classical percolation threshold.Comment: published in Nature Physics; The present version is the initial
manuscript (unchanged compared to version 1); The published version is
available online at
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys2256.htm
High-frequency homogenization for periodic media
This article is available open access through the publisher’s website at the link below. Copyright @ 2010 The Royal Society.An asymptotic procedure based upon a two-scale approach is developed for wave propagation in a doubly periodic inhomogeneous medium with a characteristic length scale of microstructure far less than that of the macrostructure. In periodic media, there are frequencies for which standing waves, periodic with the period or double period of the cell, on the microscale emerge. These frequencies do not belong to the low-frequency range of validity covered by the classical homogenization theory, which motivates our use of the term ‘high-frequency homogenization’ when perturbing about these standing waves. The resulting long-wave equations are deduced only explicitly dependent upon the macroscale, with the microscale represented by integral quantities. These equations accurately reproduce the behaviour of the Bloch mode spectrum near the edges of the Brillouin zone, hence yielding an explicit way for homogenizing periodic media in the vicinity of ‘cell resonances’. The similarity of such model equations to high-frequency long wavelength asymptotics, for homogeneous acoustic and elastic waveguides, valid in the vicinities of thickness resonances is emphasized. Several illustrative examples are considered and show the efficacy of the developed techniques.NSERC (Canada) and the EPSRC
Correlation function of weakly interacting bosons in a disordered lattice
One of the most important issues in disordered systems is the interplay of
the disorder and repulsive interactions. Several recent experimental advances
on this topic have been made with ultracold atoms, in particular the
observation of Anderson localization, and the realization of the disordered
Bose-Hubbard model. There are however still questions as to how to
differentiate the complex insulating phases resulting from this interplay, and
how to measure the size of the superfluid fragments that these phases entail.
It has been suggested that the correlation function of such a system can give
new insights, but so far little experimental investigation has been performed.
Here, we show the first experimental analysis of the correlation function for a
weakly interacting, bosonic system in a quasiperiodic lattice. We observe an
increase in the correlation length as well as a change in shape of the
correlation function in the delocalization crossover from Anderson glass to
coherent, extended state. In between, the experiment indicates the formation of
progressively larger coherent fragments, consistent with a fragmented BEC, or
Bose glass.Comment: 16 pages, 8 figure
Correlated electrons in the presence of disorder
Several new aspects of the subtle interplay between electronic correlations
and disorder are reviewed. First, the dynamical mean-field theory
(DMFT)together with the geometrically averaged ("typical") local density of
states is employed to compute the ground state phase diagram of the
Anderson-Hubbard model at half-filling. This non-perturbative approach is
sensitive to Anderson localization on the one-particle level and hence can
detect correlated metallic, Mott insulating and Anderson insulating phases and
can also describe the competition between Anderson localization and
antiferromagnetism. Second, we investigate the effect of binary alloy disorder
on ferromagnetism in materials with -electrons described by the periodic
Anderson model. A drastic enhancement of the Curie temperature caused by
an increase of the local -moments in the presence of disordered conduction
electrons is discovered and explained.Comment: 17 pages, 7 figures, final version, typos corrected, references
updated, submitted to Eur. Phys. J. for publication in the Special Topics
volume "Cooperative Phenomena in Solids: Metal-Insulator Transitions and
Ordering of Microscopic Degrees of Freedom
Master crossover behavior of parachor correlations for one-component fluids
The master asymptotic behavior of the usual parachor correlations, expressing
surface tension as a power law of the density difference
between coexisting liquid and vapor, is analyzed for a
series of pure compounds close to their liquid-vapor critical point, using only
four critical parameters , , and ,
for each fluid.
... The main consequences of these theoretical estimations are discussed in
the light of engineering applications and process simulations where parachor
correlations constitute one of the most practical method for estimating surface
tension from density and capillary rise measurements
Disordered ultracold atomic gases in optical lattices: A case study of Fermi-Bose mixtures
We present a review of properties of ultracold atomic Fermi-Bose mixtures in
inhomogeneous and random optical lattices. In the strong interacting limit and
at very low temperatures, fermions form, together with bosons or bosonic holes,
{\it composite fermions}. Composite fermions behave as a spinless interacting
Fermi gas, and in the presence of local disorder they interact via random
couplings and feel effective random local potential. This opens a wide variety
of possibilities of realizing various kinds of ultracold quantum disordered
systems. In this paper we review these possibilities, discuss the accessible
quantum disordered phases, and methods for their detection. The discussed
quantum phases include Fermi glasses, quantum spin glasses, "dirty"
superfluids, disordered metallic phases, and phases involving quantum
percolation.Comment: 29 pages and 11 figure
A search for resonant production of pairs in $4.8\ \rm{fb}^{-1}p\bar{p}\sqrt{s}=1.96\ \rm{TeV}$
We search for resonant production of tt pairs in 4.8 fb^{-1} integrated
luminosity of ppbar collision data at sqrt{s}=1.96 TeV in the lepton+jets decay
channel, where one top quark decays leptonically and the other hadronically. A
matrix element reconstruction technique is used; for each event a probability
density function (pdf) of the ttbar candidate invariant mass is sampled. These
pdfs are used to construct a likelihood function, whereby the cross section for
resonant ttbar production is estimated, given a hypothetical resonance mass and
width. The data indicate no evidence of resonant production of ttbar pairs. A
benchmark model of leptophobic Z \rightarrow ttbar is excluded with m_{Z'} <
900 GeV at 95% confidence level.Comment: accepted for publication in Physical Review D Sep 21, 201
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