arXiv subjects

P. Voisin

Publications and source records attributed to P. Voisin.

22 records · Page 2Linked to original sources

arXiv2007

Electron spin quantum beats in positively charged quantum dots: nuclear field effects

We have studied the electron spin coherence in an ensemble of positively charged InAs/GaAs quantum dots. In a transverse magnetic field, we show that two main contributions must be taken into account to explain the damping of the circular polarization oscillations. The first one is due to the nuclear field fluctuations from dot to dot experienced by the electron spin. The second one is due to the dispersion of the transverse electron Lande g-factor, due to the inherent inhomogeneity of the system, and leads to a field dependent contribution to the damping. We have developed a model taking into account both contributions, which is in good agreement with the experimental data. This enables us to extract the pure contribution to dephasing due to the nuclei.

cond-mat.mtrl-sci↗

arXiv2007

Tetragonal and trigonal deformations in zinc-blende semiconductors : a tight-binding point of view

The deformation potentials of cubic semiconductors are re-examined from the point of view of the extended-basis $sp^3d^5s^*$ tight-binding model. Previous parametrizations had failed to account properly for trigonal deformations, even leading to incorrect sign of the acoustic component of the shear deformation potential {\it d}. The strain-induced shifts and splittings of the on-site energies of the p- and d-orbitals are shown to play a prominent role in obtaining satisfactory values of deformation potentials both at the zone center and zone extrema. The present approach results in excellent agreement with available experimental data and ab-initio calculations.

cond-mat.mtrl-sci↗

arXiv2006

Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots

We show that optical pumping of electron spins in individual InGaAs quantum dots leads to strong nuclear polarisation that we measure via the Overhauser shift (OHS) in magneto-photoluminescence experiments between 0 and 4T. We find a strongly non-monotonous dependence of the OHS on the applied magnetic field, with a maximum nuclear polarisation of 40% for intermediate magnetic fields. We observe that the OHS is larger for nuclear fields anti-parallel to the external field than in the parallel configuration. A bistability in the dependence of the OHS on the spin polarization of the optically injected electrons is found. All our findings are qualitatively understood with a model based on a simple perturbative approach.

cond-mat.mes-hall↗

arXiv2006

Manipulating the exciton fine structure of single CdTe/ZnTe quantum dots by an in-plane magnetic field

Polarization resolved photoluminescence (PL) spectroscopy of individual CdTe/ZnTe quantum dots is investigated in the presence of external in-plane magnetic field. We find that the excitonic fine structure strongly depends on the magnitude and direction of applied field. The splitting between "bright" and "dark" states increases with the magnetic field, whereas the anisotropic exchange splitting of the bright excitons can be reduced or enhanced, depending on the field direction. Increase (decrease) is observed when the field is applied parallel to the PL polarization direction of the lower (upper) energy exciton. For intermediate fields, we observe a rotation of the PL polarization orientation. The results are discussed in terms of an effective spin Hamiltonian derived for the exciton ground state.

cond-mat.other↗