Optical alignment and polarization conversion of neutral exciton spin in individual InAs/GaAs quantum dots

We investigate exciton spin memory in individual InAs/GaAs self-assembled quantum dots via optical alignment and conversion of exciton polarization in a magnetic field. Quasiresonant phonon-assisted excitation is successfully employed to define the initial spin polarization of neutral excitons. The conservation of the linear polarization generated along the bright exciton eigenaxes of up to 90% and the conversion from circular- to linear polarization of up to 47% both demonstrate a very long spin relaxation time with respect to the radiative lifetime. Results are quantitatively compared with a model of pseudo-spin 1/2 including heavy-to-light hole mixing.Comment: 5 pages, 3 figure

Optically probing the fine structure of a single Mn atom in an InAs quantum dot

We report on the optical spectroscopy of a single InAs/GaAs quantum dot (QD) doped with a single Mn atom in a longitudinal magnetic field of a few Tesla. Our findings show that the Mn impurity is a neutral acceptor state A^0 whose effective spin J=1 is significantly perturbed by the QD potential and its associated strain field. The spin interaction with photo-carriers injected in the quantum dot is shown to be ferromagnetic for holes, with an effective coupling constant of a few hundreds of micro-eV, but vanishingly small for electrons.Comment: 5 pages, 3 figure

A tunable, dual mode field-effect or single electron transistor

A dual mode device behaving either as a field-effect transistor or a single electron transistor (SET) has been fabricated using silicon-on-insulator metal oxide semiconductor technology. Depending on the back gate polarisation, an electron island is accumulated under the front gate of the device (SET regime), or a field-effect transistor is obtained by pinching off a bottom channel with a negative front gate voltage. The gradual transition between these two cases is observed. This dual function uses both vertical and horizontal tunable potential gradients in non-overlapped silicon-on-insulator channel

Efficient dynamical nuclear polarization in quantum dots: Temperature dependence

We investigate in micro-photoluminescence experiments the dynamical nuclear polarization in individual InGaAs quantum dots. Experiments carried out in an applied magnetic field of 2T show that the nuclear polarization achieved through the optical pumping of electron spins is increasing with the sample temperature between 2K and 55K, reaching a maximum of about 50%. Analysing the dependence of the Overhauser shift on the spin polarization of the optically injected electron as a function of temperature enables us to identify the main reasons for this increase.Comment: 5 pages, 3 figure

Intrinsic interface states in InAs-AlSb heterostructures

We examine the possibility of intrinsic interface states bound to the plane of In-Sb chemical bonds at InAs/AlSb interfaces. Careful parameterization of the bulk materials in the frame of the extended basis spds^* tight-binding model and recent progress in predictions of band offsets severely limit the span of tight-binding parameters describing this system. We find that a heavy-hole like interface state bound to the plane of In-Sb bonds exists for a large range of values of the InSb/InAs band offset