2,219 research outputs found
Room temperature magneto-optic effect in silicon light-emitting diodes
In weakly spin-orbit coupled materials, the spin-selective nature of
recombination can give rise to large magnetic-field effects, for example on
electro-luminescence from molecular semiconductors. While silicon has weak
spin-orbit coupling, observing spin-dependent recombination through
magneto-electroluminescence is challenging due to the inefficiency of emission
due to silicon's indirect band-gap, and to the difficulty in separating
spin-dependent phenomena from classical magneto-resistance effects. Here we
overcome these challenges to measure magneto-electroluminescence in silicon
light-emitting diodes fabricated via gas immersion laser doping. These devices
allow us to achieve efficient emission while retaining a well-defined geometry
thus suppressing classical magnetoresistance effects to a few percent. We find
that electroluminescence can be enhanced by up to 300\% near room temperature
in a seven Tesla magnetic field showing that the control of the spin degree of
freedom can have a strong impact on the efficiency of silicon LEDs
Ks band secondary eclipses of WASP-19b and WASP-43b with the Anglo-Australian Telescope
We report new Ks band secondary eclipse observations for the hot-Jupiters
WASP-19b and WASP-43b. Using the IRIS2 infrared camera on the Anglo-Australian
Telescope (AAT), we measured significant secondary eclipses for both planets,
with depths of 0.287 -0.020/+0.020% and 0.181 -0.027/+0.027% for WASP-19b and
WASP-43b respectively. We compare the observations to atmosphere models from
the VSTAR line-by-line radiative transfer code, and examine the effect of C/O
abundance, top layer haze, and metallicities on the observed spectra. We
performed a series of signal injection and recovery exercises on the observed
light curves to explore the detection thresholds of the AAT+IRIS2 facility. We
find that the optimal photometric precision is achieved for targets brighter
than Kmag = 9, for which eclipses as shallow as 0.05% are detectable at >5
sigma significance.Comment: Accepted for publication in MNRAS, 13 pages, 10 figure
The Mass Distribution of the Strong Lensing Cluster SDSS J1531+3414
We present the mass distribution at the core of SDSS J1531+3414, a
strong-lensing cluster at z=0.335. We find that the mass distribution is well
described by two cluster-scale halos with a contribution from cluster-member
galaxies. New HST observations of SDSS J1531+3414 reveal a signature of ongoing
star formation associated with the two central galaxies at the core of the
cluster, in the form of a chain of star forming regions at the center of the
cluster. Using the lens model presented here, we place upper limits on the
contribution of a possible lensed image to the flux at the center region, and
rule out that this emission is coming from a background source.Comment: 8 pages, 5 figures; Submitted to Ap
A clumpy and anisotropic galaxy halo at z=1 from gravitational-arc tomography
Every star-forming galaxy has a halo of metal-enriched gas extending out to
at least 100 kpc, as revealed by the absorption lines this gas imprints on the
spectra of background quasars. However, quasars are sparse and typically probe
only one narrow pencil beam through the intervening galaxy. Close quasar pairs
and gravitationally lensed quasars have been used to circumvent this inherently
one-dimensional technique, but these objects are rare and the structure of the
circum-galactic medium remains poorly constrained. As a result, our
understanding of the physical processes that drive the re-cycling of baryons
across the lifetime of a galaxy is limited. Here we report integral-field
(tomographic) spectroscopy of an extended background source -a bright giant
gravitational arc. We can thus coherently map the spatial and kinematic
distribution of Mg II absorption -a standard tracer of enriched gas- in an
intervening galaxy system at redshift 0.98 (i.e., ~8 Gyr ago). Our
gravitational-arc tomography unveils a clumpy medium in which the
absorption-strength decreases with increasing impact parameter, in good
agreement with the statistics towards quasars; furthermore, we find strong
evidence that the gas is not distributed isotropically. Interestingly, we
detect little kinematic variation over a projected area of ~600 kpc squared,
with all line-of-sight velocities confined to within a few tens of km/s of each
other. These results suggest that the detected absorption originates from
entrained recycled material, rather than in a galactic outflow.Comment: Published online in Nature on 31 January 201
Optically addressable molecular spins for quantum information processing
Spin-bearing molecules are promising building blocks for quantum technologies
as they can be chemically tuned, assembled into scalable arrays, and readily
incorporated into diverse device architectures. In molecular systems, optically
addressing ground-state spins would enable a wide range of applications in
quantum information science, as has been demonstrated for solid-state defects.
However, this important functionality has remained elusive for molecules. Here,
we demonstrate such optical addressability in a series of synthesized
organometallic, chromium(IV) molecules. These compounds display a ground-state
spin that can be initialized and read out using light, and coherently
manipulated with microwaves. In addition, through atomistic modification of the
molecular structure, we tune the spin and optical properties of these
compounds, paving the way for designer quantum systems synthesized from the
bottom-up.Comment: 9 pages, 4 figure
Star Formation at z=2.481 in the Lensed Galaxy SDSS J1110+6459, I: Lens Modeling and Source Reconstruction
Using the combined resolving power of the Hubble Space Telescope and
gravitational lensing, we resolve star-forming structures in a z~2.5 galaxy on
scales much smaller than the usual kiloparsec diffraction limit of HST. SGAS
J111020.0+645950.8 is a clumpy, star forming galaxy lensed by the galaxy
cluster SDSS J1110+6459 at z = 0.659, with a total magnification ~30x across
the entire arc. We use a hybrid parametric/non-parametric strong lensing mass
model to compute the deflection and magnification of this giant arc,
reconstruct the light distribution of the lensed galaxy in the source plane,
and resolve the star formation into two dozen clumps. We develop a
forward-modeling technique to model each clump in the source plane. We ray
trace the model to the image plane, convolve with the instrumental point spread
function (PSF), and compare with the GALFIT model of the clumps in the image
plane, which decomposes clump structure from more extended emission. This
technique has the advantage, over ray tracing, by accounting for the asymmetric
lensing shear of the galaxy in the image plane and the instrument PSF. At this
resolution, we can begin to study star formation on a clump-by-clump basis,
toward the goal of understanding feedback mechanisms and the buildup of
exponential disks at high redshift.Comment: 19 pages, 12 figures, accepted to Ap
Gaze cueing elicited by emotional faces is influenced by affective context
When we observe someone shift their gaze to a peripheral event or object, a corresponding shift in our own attention often follows. This social orienting response, joint attention, has been studied in the laboratory using the gaze cueing paradigm. Here, we investigate the combined influence of the emotional content displayed in two critical components of a joint attention episode: The facial expression of the cue face, and the affective nature of the to-be-localized target object. Hence, we presented participants with happy and disgusted faces as cueing stimuli, and neutral (Experiment 1), pleasant and unpleasant (Experiment 2) pictures as target stimuli. The findings demonstrate an effect of ‘emotional context’ confined to participants viewing pleasant pictures. Specifically, gaze cueing was boosted when the emotion of the gazing face (i.e., happy) matched that of the targets (pleasant). Demonstrating modulation by emotional context highlights the vital flexibility that a successful joint attention system requires in order to assist our navigation of the social world
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