49 research outputs found
Signature of the Overhauser field on the coherent spin dynamics of donor-bound electron in a single CdTe quantum well
We have studied the coherent spin dynamics in an oblique magnetic field of
electrons localized on donors and placed in the middle of a single CdTe quantum
well, by using a time-resolved optical technique: the photo-induced Faraday
rotation. We showed that this dynamics is affected by a weak Overhauser field
created via the hyperfine interaction of optically spin-polarized donor-bound
electrons with the surrounding nuclear isotopes carrying non-zero spins. We
have measured this nuclear field, which is on the order of a few mT and can
reach a maximum experimental value of 9.4 mT. This value represents 13 % of the
maximal nuclear polarization, and corresponds also to 13 % of maximal
electronic polarization.Comment: 15 pages, 4 figure
Hole spin dephasing time associated to hyperfine interaction in quantum dots
The spin interaction of a hole confined in a quantum dot with the surrounding
nuclei is described in terms of an effective magnetic field. We show that, in
contrast to the Fermi contact hyperfine interaction for conduction electrons,
the dipole-dipole hyperfine interaction is anisotropic for a hole, for both
pure or mixed hole states. We evaluate the coupling constants of the
hole-nuclear interaction and demonstrate that they are only one order of
magnitude smaller than the coupling constants of the electron-nuclear
interaction. We also study, theoretically, the hole spin dephasing of an
ensemble of quantum dots via the hyperfine interaction in the framework of
frozen fluctuations of the nuclear field, in absence or in presence of an
applied magnetic field. We also discuss experiments which could evidence the
dipole-dipole hyperfine interaction and give information on hole mixing.Comment: 35 pages, 7 figures and 2 table
Enhancement of the electron spin memory by localization on donors in a quantum well
We present easily reproducible experimental conditions giving long electron
spin relaxation and dephasing times at low temperature in a quantum well. The
proposed system consists in an electron localized by a donor potential, and
immerged in a quantum well in order to improve its localization with respect to
donor in bulk. We have measured, by using photoinduced Faraday rotation
technique, the spin relaxation and dephasing times of electrons localized on
donors placed in the middle of a 80A CdTe quantum well, and we have obtained
15ns and 18ns, respectively, which are almost two orders of magnitude longer
than the free electron spin relaxation and dephasing times obtained previously
in a similar CdTe quantum well (J. Tribollet et al. PRB 68, 235316 (2003)).Comment: 15 pages, 4 figure
Dark States and Interferences in Cascade Transitions of Ultra-Cold Atoms in a Cavity
We examine the competition among one- and two-photon processes in an
ultra-cold, three-level atom undergoing cascade transitions as a result of its
interaction with a bimodal cavity. We show parameter domains where two-photon
transitions are dominant and also study the effect of two-photon emission on
the mazer action in the cavity. The two-photon emission leads to the loss of
detailed balance and therefore we obtain the photon statistics of the cavity
field by the numerical integration of the master equation. The photon
distribution in each cavity mode exhibits sub- and super- Poissonian behaviors
depending on the strength of atom-field coupling. The photon distribution
becomes identical to a Poisson distribution when the atom-field coupling
strengths of the modes are equal.Comment: 15 pages including 7 figures in Revtex, submitted to PR
Spin decoherence and relaxation processes in zero-dimensional semiconductor nanostructures
International audienceIn recent years, interest in spin physics has been renewed due to its potential application in spintronics and quantum information. In these frameworks, the main required property is the presence of long spin memory. We present a short review of recent results concerning spin decoherence and relaxation processes in zero-dimensional (0D) nanostructures, especially in quantum dots
Anisotropic spin splitting of the electron ground state in InAs quantum dots
International audiencePhotoinduced circular dichroism experiments in an oblique magnetic field allow measurements of Larmor precession frequencies, and so give a precise determination of the electron Lande g factor and its anisotropy in self-assembled InAs/GaAs quantum dots emitting at 1.32 eV. In good agreement with recent theoretical results, the authors measure parallel to g(perpendicular to)parallel to=0.397 +/- 0.003 and parallel to g(parallel to)parallel to=0.18 +/- 0.02. (c) 2007 American Institute of Physics