218 research outputs found
Anomalous tunneling conductances of a spin singlet \nu=2/3 edge states: Interplay of Zeeman splitting and Long Range Coulomb Interaction
The point contact tunneling conductance between edges of the spin singlet
quantum Hall states is studied both in the
quasiparticle tunneling picture and in the electron tunneling picture. Due to
the interplay of Zeeman splitting and the long range Coulomb interaction
between edges of opposite chirality novel spin excitations emerge, and their
effect is characterized by anomalous exponents of the charge and spin tunneling
conductances in various temperature ranges. Depending on the kinds of
scatterings at the point contact and the tunneling mechanism the anomalous
interaction in spin sector may enhance or suppress the tunneling conductances.
The effects of novel spin excitation are also relevant to the recent NMR
experiments on quantum Hall edges.Comment: Revtex File, 7 pages: To be published in Physical Reviews
The Ground State of a Two-Dimensional Electron Liquid in a Weak Magnetic Field
We study the ground state of a clean two-dimensional electron liquid in a
weak magnetic field where lower Landau levels are completely filled
and the upper level is partially filled. It is shown that the electrons at the
upper Landau level form domains with filling factor equal to one and zero. The
domains alternate with a spatial period of the order of the cyclotron radius,
which is much larger than the interparticle distance at the upper Landau level.
The one-particle density of states, which can be probed by tunneling
experiments, is shown to have a pseudogap linearly dependent on the magnetic
field in the limit of large .Comment: REVTeX, 21 pages + 12 figures in PostScript. Uses amsfonts.sty,
multicol.sty, and psfig.st
A Catalog of Spectroscopically Confirmed White Dwarfs from the Sloan Digital Sky Survey Data Release 4
We present a catalog of 9316 spectroscopically confirmed white dwarfs from
the Sloan Digital Sky Survey Data Release 4. We have selected the stars through
photometric cuts and spectroscopic modeling, backed up by a set of visual
inspections. Roughly 6000 of the stars are new discoveries, roughly doubling
the number of spectroscopically confirmed white dwarfs. We analyze the stars by
performing temperature and surface gravity fits to grids of pure hydrogen and
helium atmospheres. Among the rare outliers are a set of presumed helium-core
DA white dwarfs with estimated masses below 0.3 Msun, including two candidates
that may be the lowest masses yet found. We also present a list of 928 hot
subdwarfs.Comment: Accepted by the Astrophysical Journal Supplements, 25 pages, 24
figures, LaTeX. The electronic catalog, as well as diagnostic figures and
links to the spectra, is available at http://das.sdss.org/wdcat/dr4
Quantum-Hall Quantum-Bits
Bilayer quantum Hall systems can form collective states in which electrons
exhibit spontaneous interlayer phase coherence. We discuss the possibility of
using bilayer quantum dot many-electron states with this property to create
two-level systems that have potential advantages as quantum bits.Comment: 4 pages, 4 figures included, version to appear in Phys. Rev. B (Rapid
Communications
Composite Fermion Description of Correlated Electrons in Quantum Dots: Low Zeeman Energy Limit
We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}Comment: 15 pages, 7 postscript figure
SDSS J092455.87+021924.9: an Interesting Gravitationally Lensed Quasar from the Sloan Digital Sky Survey
We report the discovery of a new gravitationally lensed quasar from the Sloan
Digital Sky Survey, SDSS J092455.87+021924.9 (SDSS J0924+0219). This object was
selected from among known SDSS quasars by an algorithm that was designed to
select another known SDSS lensed quasar (SDSS 1226-0006A,B). Five separate
components, three of which are unresolved, are identified in photometric
follow-up observations obtained with the Magellan Consortium's 6.5m Walter
Baade telescope at Las Campanas Observatory. Two of the unresolved components
(designated A and B) are confirmed to be quasars with z=1.524; the velocity
difference is less than 100 km sec^{-1} according to spectra taken with the W.
M. Keck Observatory's Keck II telescope on Mauna Kea. A third stellar
component, designated C, has the colors of a quasar with redshift similar to
components A and B. The maximum separation of the point sources is 1.78". The
other two sources, designated G and D, are resolved. Component G appears to be
the best candidate for the lensing galaxy. Although component D is near the
expected position of the fourth lensed component in a four image lens system,
its properties are not consistent with being the image of a quasar at z~1.5.
Nevertheless, the identical redshifts of components A and B and the presence of
component C strongly suggest that this object is a gravitational lens. Our
observations support the idea that a foreground object reddens the fourth
lensed component and that another unmodeled effect (such as micro- or
milli-lensing) demagnificates it, but we cannot rule out the possibility that
SDSS0924+0219 is an example of the relatively rare class of ``three component''
lens systems.Comment: 24 pages, 6 figures, accepted by A
Spontaneous Coherence and Collective Modes in Double-Layer Quantum Dot Systems
We study the ground state and the collective excitations of
parabolically-confined double-layer quantum dot systems in a strong magnetic
field. We identify parameter regimes where electrons form maximum density
droplet states, quantum-dot analogs of the incompressible states of the bulk
integer quantum Hall effect. In these regimes the Hartree-Fock approximation
and the time-dependent Hartree-Fock approximations can be used to describe the
ground state and collective excitations respectively. We comment on the
relationship between edge excitations of dots and edge magneto-plasmon
excitations of bulk double-layer systems.Comment: 20 pages (figures included) and also available at
http://fangio.magnet.fsu.edu/~jhu/Paper/qdot_cond.ps, replaced to fix figure
Testing the Cosmological Constant as a Candidate for Dark Energy
It may be difficult to single out the best model of dark energy on the basis
of the existing and planned cosmological observations, because many different
models can lead to similar observational consequences. However, each particular
model can be studied and either found consistent with observations or ruled
out. In this paper, we concentrate on the possibility to test and rule out the
simplest and by far the most popular of the models of dark energy, the theory
described by general relativity with positive vacuum energy (the cosmological
constant). We evaluate the conditions under which this model could be ruled out
by the future observations made by the Supernova/Acceleration Probe SNAP (both
for supernovae and weak lensing) and by the Planck Surveyor cosmic microwave
background satellite.Comment: 6 pages, 2 figures, revtex
Economics methods in Cochrane systematic reviews of health promotion and public health related interventions.
Peer reviewedPublisher PD
SDSSJ103913.70+533029.7: A Super Star Cluster in the Outskirts of a Galaxy Merger
We describe the serendipitous discovery in the spectroscopic data of the
Sloan Digital Sky Survey of a star-like object, SDSSJ103913.70+533029.7, at a
heliocentric radial velocity of +1012 km/s. Its proximity in position and
velocity to the spiral galaxy NGC 3310 suggests an association with the galaxy.
At this distance, SDSSJ103913.70+533029.7 has the luminosity of a super star
cluster and a projected distance of 17 kpc from NGC 3310. Its spectroscopic and
photometric properties imply a mass of > 10^6 solar masses and an age close to
that of the tidal shells seen around NGC 3310, suggesting that it formed in the
event which formed the shells.Comment: Accepted by AJ: 4 figures (1 color
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