7,997 research outputs found
Binary fluid amplifier solves stability and load problems
Digital fluid amplifier has load intensity, high stability, and operates at low reynolds numbers. It contains specially designed nozzles to provide uniform exit-velocity profiles and to ensure jets of low turbulence
Finite temperature phase diagram of a polarized Fermi gas in an optical lattice
We present phase diagrams for a polarized Fermi gas in an optical lattice as
a function of temperature, polarization, and lattice filling factor. We
consider the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO), Sarma or breached pair
(BP), and BCS phases, and the normal state and phase separation. We show that
the FFLO phase appears in a considerable portion of the phase diagram. The
diagrams have two critical points of different nature. We show how various
phases leave clear signatures to momentum distributions of the atoms which can
be observed after time of flight expansion.Comment: Journal versio
Faint Field Galaxies Around Bright Stars - A New Strategy for Imaging at the Diffraction Limit
This paper presents a new strategy for observing faint galaxies with high
order natural guide star systems. We have imaged 5 high galactic latitude
fields within the isoplanatic patch of bright stars (8.5 < R < 10.3 mag). The
fields provide a rich set of faint field galaxies that are observable with a
natural guide star adaptive optics system on a large telescope. Due to the
small fields of many AO science cameras, these preliminary images are necessary
to identify candidate galaxies. We present the photometry and positions for 78
objects (at least 40 galaxies) near five bright stars, appropriate for
diffraction limited studies with the Keck and other AO systems on large
ground-based telescopes. The K band seeing conditions in each field were
excellent (0.4" - 0.7") allowing us to identify stars and estimate galaxy
sizes. We also simulate AO images of field galaxies to determine the
feasibility of infrared morphological studies at the diffraction limit. With
new high order AO systems coming on line with 8-10 meter class telescopes, we
believe these observations are invaluable in beginning to study faint galaxy
populations at the diffraction limit.Comment: 15 pages, Latex, 9 figures. Accepted for publication in P.A.S.
Modification of Born impurity scattering near the surface of d-wave superconductors and influence of external magnetic field
We study the influence of Born impurity scattering on the zero-energy Andreev
bound states near the surface of a d-wave superconductor with and without an
externally applied magnetic field. Without an external magnetic field we show
that the effect of Born impurity scattering is stronger at the surface than in
the bulk. In the presence of an external magnetic field the splitting of the
zero-energy Andreev bound states is shown to have a nonmonotonous temperature
dependence. Born impurity scattering does not wash out the peak splitting, but
instead the peak splitting is shown to be quite robust against impurities. We
also show that a nonzero gap renormalization appears near the surface.Comment: 9 pages, 17 figures; minor changes; new figure 11; accepted for
publication in Phys. Rev.
Spectral properties of a partially spin-polarized one-dimensional Hubbard/Luttinger superfluid
We calculate the excitation spectra of a spin-polarized Hubbard chain away
from half-filling, using a high-precision momentum-resolved time-dependent
Density Matrix Renormalization Group method. Focusing on the U<0 case, we
present in some detail the single-fermion, pair, density and spin spectra, and
discuss how spin-charge separation is altered for this system. The pair spectra
show a quasi-condensate at a nonzero momentum proportional to the polarization,
as expected for this Fulde-Ferrel-Larkin-Ovchinnikov-like superfluid.Comment: 4 pages, 3 low resolution color fig
Magneto-elastic quantum fluctuations and phase transitions in the iron superconductors
We examine the relevance of magneto-elastic coupling to describe the complex
magnetic and structural behaviour of the different classes of the iron
superconductors. We model the system as a two-dimensional metal whose magnetic
excitations interact with the distortions of the underlying square lattice.
Going beyond mean field we find that quantum fluctuation effects can explain
two unusual features of these materials that have attracted considerable
attention. First, why iron telluride orders magnetically at a non-nesting
wave-vector and not at the nesting wave-vector as
in the iron arsenides, even though the nominal band structures of both these
systems are similar. And second, why the magnetic transition in the
iron arsenides is often preceded by an orthorhombic structural transition.
These are robust properties of the model, independent of microscopic details,
and they emphasize the importance of the magneto-elastic interaction.Comment: 4 pages, 3 figures; minor change
Pairing of a trapped resonantly-interacting fermion mixture with unequal spin populations
We consider the phase separation of a trapped atomic mixture of fermions with
unequal spin populations near a Feshbach resonance. In particular, we determine
the density profile of the two spin states and compare with the recent
experiments of Partridge et al. (cond-mat/0511752). Overall we find quite good
agreement. We identify the remaining discrepancies and pose them as open
problems.Comment: 4 figures, 4+ pages, revtex
Neutrality of a magnetized two-flavor quark superconductor
We investigate the effect of electric and color charge neutrality on the
two-flavor color superconducting (2SC) phase of cold and dense quark matter in
presence of constant external magnetic fields and at moderate baryon densities.
Within the framework of the Nambu-Jona-Lasinio (NJL) model, we study the
inter-dependent evolution of the quark's BCS gap and constituent mass with
increasing density and magnetic field. While confirming previous results
derived for the highly magnetized 2SC phase with color neutrality alone, we
obtain new results as a consequence of imposing charge neutrality. In the
charge neutral gapless 2SC phase (g2SC), a large magnetic field drives the
color superconducting phase transition to a crossover, while the chiral phase
transition is first order. At larger diquark-to-scalar coupling ratio
, where the 2SC phase is preferred, we see hints of the
Clogston-Chandrasekhar limit at a very large value of the magnetic field
(G), but this limit is strongly affected by Shubnikov de
Haas-van Alphen oscillations of the gap, indicating the transition to a
domain-like state.Comment: 19 pages, 7 figures, Matches with the published versio
Profiles of near-resonant population-imbalanced trapped Fermi gases
We investigate the density profiles of a partially polarized trapped Fermi
gas in the BCS-BEC crossover region using mean field theory within the local
density approximation. Within this approximation the gas is phase separated
into concentric shells. We describe how the structure of these shells depends
upon the polarization and the interaction strength. A Comparison with
experiments yields insight into the possibility of a polarized superfluid
phase.Comment: 4 pages, 5 Figures, Published versio
Bose-Einstein Condensates in Strongly Disordered Traps
A Bose-Einstein condensate in an external potential consisting of a
superposition of a harmonic and a random potential is considered theoretically.
From a semi-quantitative analysis we find the size, shape and excitation
energy as a function of the disorder strength. For positive scattering length
and sufficiently strong disorder the condensate decays into fragments each of
the size of the Larkin length . This state is stable over a large
range of particle numbers. The frequency of the breathing mode scales as
. For negative scattering length a condensate of size
may exist as a metastable state. These finding are generalized to anisotropic
traps
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