1,988 research outputs found
Optical orientation of spins in GaAs:Mn/AlGaAs quantum wells via impurity-to-band excitation
The paper reports optical orientation experiments performed in the narrow
GaAs/AlGaAs quantum wells doped with Mn. We experimentally demonstrate a
control over the spin polarization by means of the optical orientation via the
impurity-to-band excitation and observe a sign inversion of the luminescence
polarization depending on the pump power. The g factor of a hole localized on
the Mn acceptor in the quantum well was also found to be considerably modified
from its bulk value due to the quantum confinement effect. This finding shows
the importance of the local environment on magnetic properties of the dopants
in semiconductor nanostructures
Strain dependence of the Mn anisotropy in ferromagnetic semiconductors observed by x-ray magnetic circular dichroism
We demonstrate sensitivity of the Mn 3d valence states to strain in the
ferromagnetic semiconductors (Ga,Mn)As and (Al,Ga,Mn)As, using x-ray magnetic
circular dichroism (XMCD). The spectral shape of the Mn XMCD is
dependent on the orientation of the magnetization, and features with cubic and
uniaxial dependence are distinguished. Reversing the strain reverses the sign
of the uniaxial anisotropy of the Mn pre-peak which is ascribed to
transitions from the Mn 2p core level to p-d hybridized valence band hole
states. With increasing carrier localization, the pre-peak intensity
increases, indicating an increasing 3d character of the hybridized holes.Comment: 4 pages plus 2 figures, accepted for publication in Physical Review
M2000 : an astrometric catalog in the Bordeaux Carte du Ciel zone +11 degrees < {delta} < +18 degrees
During four years, systematic observations have been conducted in drift scan
mode with the Bordeaux automated meridian circle in the declination band [+11 ;
+18]. The resulting astrometric catalog includes about 2 300 000 stars down to
the magnitude limit V_M=16.3. Nearly all stars (96%) have been observed at
least 6 times, the catalog being complete down to V_M=15.4. The median internal
standard error in position is about 35 mas in the V_M magnitude range [11 ;
15], which degrades to about 50 mas when the faintest stars are considered.
M2000 provides also one band photometry with a median internal standard error
of 0.04 mag. Comparisons with the Hipparcos and bright part of Tycho-2 catalogs
have enabled to estimate external errors in position to be lower than 40 mas.
In this zone and at epoch 1998, the faint part of Tycho-2 is found to have an
accuracy of 116 mas in alpha instead of 82 mas deduced from the model-based
standard errors given in the catalog.Comment: The catalogue can be fetched directly from:
ftp://cdsarc.u-strasbg.fr/cats/I/272 or queried from:
http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=I/272 More information at :
http://www.observ.u-bordeaux.fr/~soubiran/m2000.ht
Mn Interstitial Diffusion in (Ga,Mn)As
We present a combined theoretical and experimental study of the ferromagnetic
semiconductor (Ga,Mn)As which explains the remarkably large changes observed on
low temperature annealing. Careful control of the annealing conditions allows
us to obtain samples with ferromagnetic transition temperatures up to 159 K. Ab
initio calculations, and resistivity measurements during annealing, show that
the observed changes are due to out-diffusion of Mn interstitials towards the
surface, governed by an energy barrier of about 0.7-0.8 eV. The Mn interstitial
is a double donor resulting in compensation of charge carriers and suppression
of ferromagnetism. Electric fields induced by high concentrations of
substitutional Mn acceptors have a significant effect on the diffusion.Comment: 5 pages, 4 figures, submitted to Physical Review Letter
How fast is a snail’s pace? The influences of size and substrate on gastropod speed of locomotion
Terrestrial gastropods display monotaxic direct crawling. During locomotion, smooth muscle contraction stimulates a series of pedal waves that move along the ventral surface of the foot. These waves interact with a thin layer of mucus produced by the foot, propelling the animal forward. Although the mechanism by which this process occurs has been well studied, less is known about how morphological or environmental factors affect this process, and ultimately how they may alter the speed of propulsion. In this study, we tested the influences of body size, substrate type, and substrate orientation on crawling speed in the terrestrial snail Cornu aspersum. We found that substrate texture and orientation had a strong effect on speed, whereas snail body size and the presence of a conspecific trail did not. Crawling speed across rough sandpaper was the most striking, showing a clear inversely proportional relationship between the size of abrasive particle and speed. We suggest that this may be the result of substrate attributes interfering with mucus adhesion or mucus production, subsequently affecting locomotion, although gait choice or the frequency and length of each pedal wave may also play a role.PostprintPeer reviewe
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