6,704 research outputs found
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.
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
Magnetic field dependence of the superconducting gap node topology in non-centrosymmetric CePtSi
The non-centrosymmetric superconductor CePtSi is believed to have a line
node in the energy gap arising from coexistence of s-wave and p-wave pairing.
We show that a weak c-axis magnetic field will remove this line node, since it
has no topological stability against time-reversal symmetry breaking
perturbations. Conversely a field in the plane is shown to remove the
line node on some regions of the Fermi surface, while bifurcating the line node
in other directions, resulting in two 'boomerang'-like shapes. These line node
topological changes are predicted to be observable experimentally in the low
temperature heat capacity.Comment: 4 pages, 3 figure
Abrikosov flux-lines in two-band superconductors with mixed dimensionality
We study vortex structure in a two-band superconductor, in which one band is
ballistic and quasi-two-dimensional (2D), and the other is diffusive and
three-dimensional (3D). A circular cell approximation of the vortex lattice
within the quasiclassical theory of superconductivity is applied to a recently
developed model appropriate for such a two-band system [Tanaka et al 2006 Phys.
Rev. B 73, 220501(R); Tanaka et al 2007 Phys. Rev. B 75, 214512]. We assume
that superconductivity in the 3D diffusive band is "weak", i.e., mostly
induced, as is the case in MgB. Hybridization with the "weak" 3D diffusive
band has significant and intriguing influence on the electronic structure of
the "strong" 2D ballistic band. In particular, the Coulomb repulsion and the
diffusivity in the "weak" band enhance suppression of the order parameter and
enlargement of the vortex core by magnetic field in the "strong" band,
resulting in reduced critical temperature and field. Moreover, increased
diffusivity in the "weak" band can result in an upward curvature of the upper
critical field near the transition temperature. A particularly interesting
feature found in our model is the appearance of additional bound states at the
gap edge in the "strong" ballistic band, which are absent in the single-band
case. Furthermore, coupling with the "weak" diffusive band leads to reduced
band gaps and van Hove singularities of energy bands of the vortex lattice in
the "strong" ballistic band. We find these intriguing features for parameter
values appropriate for MgB.Comment: 11 pages, 14 figure
Finite-Size Scaling Critical Behavior of Randomly Pinned Spin-Density Waves
We have performed Monte Carlo studies of the 3D model with random
uniaxial anisotropy, which is a model for randomly pinned spin-density waves.
We study simple cubic lattices, using values in the
range 16 to 64, and with random anisotropy strengths of = 1, 2, 3, 6
and . There is a well-defined finite temperature critical point, ,
for each these values of . We present results for the angle-averaged
magnetic structure factor, at for . We also use
finite-size scaling analysis to study scaling functions for the critical
behavior of the specific heat, the magnetization and the longitudinal magnetic
susceptibility. Good data collapse of the scaling functions over a wide range
of is seen for = 6 and . For our finite values of the scaled magnetization function increases with below , and
appears to approach an -independent limit for large . This suggests that
the system is ferromagnetic below .Comment: 21 pages in single column format, 20 .eps files, revised and
expanded, errors corrected, submitted to PR
Shot-noise-driven escape in hysteretic Josephson junctions
We have measured the influence of shot noise on hysteretic Josephson
junctions initially in macroscopic quantum tunnelling (MQT) regime. Escape
threshold current into the resistive state decreases monotonically with
increasing average current through the scattering conductor, which is another
tunnel junction. Escape is predominantly determined by excitation due to the
wide-band shot noise. This process is equivalent to thermal activation (TA)
over the barrier at temperatures up to about four times above the critical
temperature of the superconductor. The presented TA model is in excellent
agreement with the experimental results
Superfluidity and magnetism in multicomponent ultracold fermions
We study the interplay between superfluidity and magnetism in a
multicomponent gas of ultracold fermions. Ward-Takahashi identities constrain
possible mean-field states describing order parameters for both pairing and
magnetization. The structure of global phase diagrams arises from competition
among these states as functions of anisotropies in chemical potential, density,
or interactions. They exhibit first and second order phase transition as well
as multicritical points, metastability regions, and phase separation. We
comment on experimental signatures in ultracold atoms.Comment: 4 pages, 3 figure
Discrete transverse superconducting modes in nano-cylinders
Spatial variation in the superconducting order parameter becomes significant
when the system is confined at dimensions well below the typical
superconducting coherence length. Motivated by recent experimental success in
growing single-crystal metallic nanorods, we study quantum confinement effects
on superconductivity in a cylindrical nanowire in the clean limit. For large
diameters, where the transverse level spacing is smaller than superconducting
order parameter, the usual approximations of Ginzburg-Landau theory are
recovered. However, under external magnetic field the order parameter develops
a spatial variation much stronger than that predicted by Ginzburg-Landau
theory, and gapless superconductivity is obtained above a certain field
strength. At small diameters, the discrete nature of the transverse modes
produces significant spatial variations in the order parameter with increased
average magnitude and multiple shoulders in the magnetic response.Comment: 10 pages, 8 figure
Emergence of Quintet Superfluidity in the Chain of Partially Polarized Spin-3/2 Ultracold Atom
The system of ultracold atoms with hyperfine spin might be unstable
against the formation of quintet pairs if the interaction is attractive in the
quintet channel. We have investigated the behavior of correlation functions in
a model including only s-wave interactions at quarter filling by large-scale
density-matrix renormalization-group simulations. We show that the correlations
of quintet pairs become quasi-long-ranged, when the system is partially
polarized, leading to the emergence of various mixed superfluid phases in which
BCS-like pairs carrying different magnetic moment coexist.Comment: 4 pages, 4 figures; significantly rewritten compared to the first
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