2,406 research outputs found
Enlarging and cooling the N\'eel state in an optical lattice
We propose an experimental scheme to favor both the realization and the
detection of the N\'eel state in a two-component gas of ultracold fermions in a
three-dimensional simple-cubic optical lattice. By adding three compensating
Gaussian laser beams to the standard three pairs of retroreflected lattice
beams, and adjusting the relative waists and intensities of the beams, one can
significantly enhance the size of the N\'eel state in the trap, thus increasing
the signal of optical Bragg scattering. Furthermore, the additional beams
provide for adjustment of the local chemical potential and the possibility to
evaporatively cool the gas while in the lattice. Our proposals are relevant to
other attempts to realize many-body quantum phases in optical lattices.Comment: 8 pages, 10 figures (significantly revised text and figures
Dynamics of wintering Norwegian spring-spawning herring at the entrance to Tysfjorden, December 1996
The entrance region to Tysfjorden was acoustically surveyed a total of eleven times
during the December 1996 abundance survey of the spawning stock of Norwegian
spring-spawning herring (Clupea harengus). The observations are summarized
through maps of the distribution, vertical sections, and statistical measures of acoustic
density in each of two strata. Experimental variograms are modeled, yielding
parameter values that summarize the major properties of aggregation. The collective
measures of density and aggregation portray a highly dynamic situation with strong
diel variation but a general persistence of the fish distribution over the eleven days of
its repeated observation
Nernst effect in the vortex-liquid regime of a type-II superconductor
We measure the transverse thermoelectric coefficient in
simulations of type-II superconductors in the vortex liquid regime, using the
time-dependent Ginzburg-Landau (TDGL) equation with thermal noise. Our results
are in reasonably good quantitative agreement with experimental data on cuprate
samples, suggesting that this simple model of superconducting fluctuations
contains much of the physics behind the large Nernst effect observed in these
materials.Comment: 6 pages. Expanded version of text. New Fig.
Strong-disorder renormalization for interacting non-Abelian anyon systems in two dimensions
We consider the effect of quenched spatial disorder on systems of
interacting, pinned non-Abelian anyons as might arise in disordered Hall
samples at filling fractions \nu=5/2 or \nu=12/5. In one spatial dimension,
such disordered anyon models have previously been shown to exhibit a hierarchy
of infinite randomness phases. Here, we address systems in two spatial
dimensions and report on the behavior of Ising and Fibonacci anyons under the
numerical strong-disorder renormalization group (SDRG). In order to manage the
topology-dependent interactions generated during the flow, we introduce a
planar approximation to the SDRG treatment. We characterize this planar
approximation by studying the flow of disordered hard-core bosons and the
transverse field Ising model, where it successfully reproduces the known
infinite randomness critical point with exponent \psi ~ 0.43. Our main
conclusion for disordered anyon models in two spatial dimensions is that
systems of Ising anyons as well as systems of Fibonacci anyons do not realize
infinite randomness phases, but flow back to weaker disorder under the
numerical SDRG treatment.Comment: 12 pages, 12 figures, 1 tabl
Finite Size Effects in Vortex Localization
The equilibrium properties of flux lines pinned by columnar disorder are
studied, using the analogy with the time evolution of a diffusing scalar
density in a randomly amplifying medium. Near H_{c1}, the physical features of
the vortices in the localized phase are shown to be determined by the density
of states near the band edge. As a result, H_{c1} is inversely proportional to
the logarithm of the sample size, and the screening length of the perpendicular
magnetic field decreases with temperature. For large tilt the extended ground
state turns out to wander in the plane perpendicular to the defects with
exponents corresponding to a directed polymer in a random medium, and the
energy difference between two competing metastable states in this case is
extensive. The divergence of the effective potential associated with strong
pinning centers as the tilt approaches its critical value is discussed as well.Comment: 10 pages, 2 figure
Correct extrapolation of overlap distribution in spin glasses
We study in d=3 dimensions the short range Ising spin glass with Jij=+/-1
couplings at T=0. We show that the overlap distribution is non-trivial in the
limit of large system size.Comment: 6 pages, 3 figure
A microscopic approach to critical phenomena at interfaces: an application to complete wetting in the Ising model
We study how the formalism of the Hierarchical Reference Theory (HRT) can be
extended to inhomogeneous systems. HRT is a liquid state theory which
implements the basic ideas of Wilson momentum shell renormalization group (RG)
to microscopic Hamiltonians. In the case of homogeneous systems, HRT provides
accurate results even in the critical region, where it reproduces scaling and
non-classical critical exponents. We applied the HRT to study wetting critical
phenomena in a planar geometry. Our formalism avoids the explicit definition of
effective surface Hamiltonians but leads, close to the wetting transition, to
the same renormalization group equation already studied by RG techiques.
However, HRT also provides information on the non universal quantities because
it does not require any preliminary coarse graining procedure. A simple
approximation to the infinite HRT set of equations is discussed. The HRT
evolution equation for the surface free energy is numerically integrated in a
semi-infinite three-dimensional Ising model and the complete wetting phase
transition is analyzed. A renormalization of the adsorption critical amplitude
and of the wetting parameter is observed. Our results are compared to available
Monte Carlo simulations.Comment: To be published in Phy. Rev.
VELO Module Production - Laser Test and Noise Analysis
This note describes the algorithms used to detect problems by analyzing datasets taken at different stages of module production using the hybrid readout systems
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