13,882 research outputs found
Breakdown of the Luttinger sum rule within the Mott-Hubbard insulator
The validity of the Luttinger sum rule is investigated within the prototype
tight-binding model of interacting fermions in one dimension, i.e., the t-V
model including the next-nearest neighbor hopping t' in order to break the
particle-hole symmetry. Scaling analysis of finite-system results at
half-filling reveals evident breakdown of the sum rule in the regime of large
gap at V >> t, while the sum rule appears to recover together with vanishing of
the Mott-Hubbard gap.Comment: 4 pages, 5 figure
Equilibrium topology of the intermediate state in type-I superconductors of different shapes
High-resolution magneto-optical technique was used to analyze flux patterns
in the intermediate state of bulk Pb samples of various shapes - cones,
hemispheres and discs. Combined with the measurements of macroscopic
magnetization these results allowed studying the effect of bulk pinning and
geometric barrier on the equilibrium structure of the intermediate state.
Zero-bulk pinning discs and slabs show hysteretic behavior due to geometric
barrier that results in a topological hysteresis -- flux tubes on penetration
and lamellae on flux exit. (Hemi)spheres and cones do not have geometric
barrier and show no hysteresis with flux tubes dominating the intermediate
field region. It is concluded that flux tubes represent the equilibrium
topology of the intermediate state in reversible samples, whereas laminar
structure appears in samples with magnetic hysteresis (either bulk or
geometric). Real-time video is available in
http://www.cmpgroup.ameslab.gov/supermaglab/video/Pb.html
NOTE: the submitted images were severely downsampled due to Arxiv's
limitations of 1 Mb total size
Slow light in moving media
We review the theory of light propagation in moving media with extremely low
group velocity. We intend to clarify the most elementary features of
monochromatic slow light in a moving medium and, whenever possible, to give an
instructive simplified picture
Classical Rotons in Cold Atomic Traps
We predict the emergence of a roton minimum in the dispersion relation of
elementary excitations in cold atomic gases in the presence of diffusive light.
In large magneto-topical traps, multiple-scattering of light is responsible for
the collective behavior of the system, which is associated to an effective
Coulomb-like interaction between the atoms. In optically thick clouds, the
re-scattered light undergoes diffusive propagation, which is responsible for a
stochastic short-range force acting on the atoms. We show that the dynamical
competition between these two forces results on a new polariton mode, which
exhibits a roton minimum. Making use of Feynman's formula for the static
structure factor, we show that the roton minimum is related to the appearance
of long-range order in the system.Comment: 5 pages, 3 figure
Formation and Equilibrium Properties of Living Polymer Brushes
Polydisperse brushes obtained by reversible radical chain polymerization
reaction onto a solid substrate with surface-attached initiators, are studied
by means of an off-lattice Monte Carlo algorithm of living polymers (LP).
Various properties of such brushes, like the average chain length and the
conformational orientation of the polymers, or the force exerted by the brush
on the opposite container wall, reveal power-law dependence on the relevant
parameters. The observed molecular weight distribution (MWD) of the grafted LP
decays much more slowly than the corresponding LP bulk system due to the
gradient of the monomer density within the dense pseudo-brush which favors
longer chains. Both MWD and the density profiles of grafted polymers and chain
ends are well fitted by effective power laws whereby the different exponents
turn out to be mutually self-consistent for a pseudo-brush in the
strong-stretching regime.Comment: 33 pages, 11 figues, J.Chem. Phys. accepted Oct. 199
Magneto-controlled nonlinear optical materials
We exploit theoretically a magneto-controlled nonlinear optical material
which contains ferromagnetic nanoparticles with a non-magnetic metallic
nonlinear shell in a host fluid. Such an optical material can have anisotropic
linear and nonlinear optical properties and a giant enhancement of
nonlinearity, as well as an attractive figure of merit.Comment: 11 pages, 2 figures. To be published in Appl. Phys. Let
Anomalous Attenuation of Transverse Sound in 3He
We present the first measurements of the attenuation of transverse sound in
superfluid 3He-B. We use fixed path length interferometry combined with the
magneto-acoustic Faraday effect to vary the effective path length by a factor
of two, resulting in absolute values of the attenuation. We find that
attenuation is significantly larger than expected from the theoretical
dispersion relation, in contrast to the phase velocity of transverse sound. We
suggest that the anomalous attenuation can be explained by surface Andreev
bound states.Comment: 4 pages, 5 figures, accepted to Phys. Rev. Let
Concentration and mass dependence of transport coefficients and correlation functions in binary mixtures with high mass-asymmetry
Correlation functions and transport coefficients of self-diffusion and shear
viscosity of a binary Lennard-Jones mixture with components differing only in
their particle mass are studied up to high values of the mass ratio ,
including the limiting case , for different mole fractions .
Within a large range of and the product of the diffusion coefficient
of the heavy species and the total shear viscosity of the mixture
is found to remain constant, obeying a generalized Stokes-Einstein
relation. At high liquid density, large mass ratios lead to a pronounced cage
effect that is observable in the mean square displacement, the velocity
autocorrelation function and the van Hove correlation function
Superfluidity and excitations at unitarity
We present lattice results for spin-1/2 fermions at unitarity, where the
effective range of the interaction is zero and the scattering length is
infinite. We measure the spatial coherence of difermion pairs for a system of
6, 10, 14, 18, 22, 26 particles with equal numbers of up and down spins in a
periodic cube. Using Euclidean time projection, we analyze ground state
properties and transient behavior due to low-energy excitations. At
asymptotically large values of t we see long-range order consistent with
spontaneously broken U(1) fermion-number symmetry and a superfluid ground
state. At intermediate times we see exponential decay in the t-dependent signal
due to an unknown low-energy excitation. We probe this low-energy excitation
further by calculating two-particle correlation functions. We find that the
excitation has the properties of a chain of particles extending across the
periodic lattice.Comment: 40 pages, 19 figures, revised version includes new data on
two-particle density correlation
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