571 research outputs found
Spin dynamics of a Mn atom in a semiconductor quantum dot under resonant optical excitation
We analyze the spin dynamics of an individual magnetic atom (Mn) inserted in
a II-VI semiconductor quantum dot under resonant optical excitation. In
addition to standard optical pumping expected for a resonant excitation, we
show that for particular conditions of laser detuning and excitation intensity,
the spin population can be trapped in the state which is resonantly excited.
This effect is modeled considering the coherent spin dynamics of the coupled
electronic and nuclear spin of the Mn atom optically dressed by a resonant
laser field. This spin population trapping mechanism is controlled by the
combined effect of the coupling with the laser field and the coherent
interaction between the different Mn spin states induced by an anisotropy of
the strain in the plane of the quantum dot
Optical control of the spin state of two Mn atoms in a quantum dot
We report on the optical spectroscopy of the spin of two magnetic atoms (Mn)
embedded in an individual quantum dot interacting with either a single
electron, a single exciton and single trion. As a result of their interaction
to a common entity, the Mn spins become correlated. The dynamics of this
process is probed by time resolved spectroscopy, that permits to determine the
optical orientation time in the range of a few tens of . In addition, we
show that the energy of the collective spin states of the two Mn atoms can be
tuned through the optical Stark effect induced by a resonant laser field
Étude de l'activité phosphatasique particulaire au sein d'un écosystème pollué : le port de Toulon
L'activité phosphatasique a été mesurée sur le matériel particulaire obtenu par filtration d'eau de mer sur des membranes de 90 µm, 5 µm et 0,25 µm de vide de maille, de décembre 1999 à mars 2000. Le substrat utilisé est du paranitrophénylphosphate (pNPP) dissous dans l'eau de mer. Dans ces conditions, deux types d'activités, à faible et à forte affinités, ont été caractérisés pour chaque classe de taille. La contribution de la classe de taille comprise entre 0,25 et 5 µm à l'ensemble de l'activité a été la plus faible des trois fractions, alors que celle de la classe de taille supérieure à 90 µm a souvent été la plus forte. Des activités associées à la présence de bactéries ont été mises en évidence sur les fractions zooplanctonique et phytoplanctonique. Toutefois, celles-ci n'ont pu rendre compte de la totalité des activités mesurées, en particulier pour le zooplancton.Phosphatase activity was estimated on particulate material resulting from filtration of sea water on 90, 5 and 0.25 µm membranes, from December 1999 to March 2000 in Toulon seaport. Para-nitrophenylphosphate (pNPP) dissolved in seawater was used as substrate. In these conditions, activities with low and high affinities were disclosed on each size class. The contribution of the 0.25-5 µm fraction was low, whereas the activity of the size class superior to 90 µm was elevated. Enzyme activities of fixed bacteria were characterized in the zooplanktonic and phytoplanktonic fractions. However, they cannot explain the totality of the measured activities in particular for zooplankton
Dynamic binding of driven interfaces in coupled ultrathin ferromagnetic layers
We demonstrate experimentally dynamic interface binding in a system
consisting of two coupled ferromagnetic layers. While domain walls in each
layer have different velocity-field responses, for two broad ranges of the
driving field, H, walls in the two layers are bound and move at a common
velocity. The bound states have their own velocity-field response and arise
when the isolated wall velocities in each layer are close, a condition which
always occurs as H->0. Several features of the bound states are reproduced
using a one dimensional model, illustrating their general nature.Comment: 5 pages, 4 figures, to be published in Physical Review Letter
Spin injection in Silicon at zero magnetic field
In this letter, we show efficient electrical spin injection into a SiGe based
\textit{p-i-n} light emitting diode from the remanent state of a
perpendicularly magnetized ferromagnetic contact. Electron spin injection is
carried out through an alumina tunnel barrier from a Co/Pt thin film exhibiting
a strong out-of-plane anisotropy. The electrons spin polarization is then
analysed through the circular polarization of emitted light. All the light
polarization measurements are performed without an external applied magnetic
field \textit{i.e.} in remanent magnetic states. The light polarization as a
function of the magnetic field closely traces the out-of-plane magnetization of
the Co/Pt injector. We could achieve a circular polarization degree of the
emitted light of 3 % at 5 K. Moreover this light polarization remains almost
constant at least up to 200 K.Comment: accepted in AP
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