Dynamics of charged excitons in GaAs quantum wells under high magnetic field

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Exciton states in semiconductor nanostructures with disorder exhibit level repulsion, a concept known from random matrix theory. Its manifestations in time-resolved Rayleigh spectra and in the autocorrelation of optical nearfield spectra are explained, and available experimental results are critically discussed. It is proposed to investigate the intrasubband absorption in quantum wells with emphasis on the aspects of level repulsion. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The ac loss of superconducting composite depends strongly on coupling between superconducting filaments via the resistive matrix. The established technique for loss reduction using twisted filaments relies on the decoupling of the filaments below a critical coupling field Bc, which increases with the reduction of the twist pitch and the matrix conductivity. Although the concept of Bc may be clearly demonstrated using two infinite slabs of finite length, further details on its correlation with the filament/c

We have measured the giant magnetoimpedance (GMI) and giant magnetoresistance (GMR) of Metglas®/Cu/Metglas trilayer stacks of micropatterned amorphous magnetic Metglas 2714a ribbons and Cu foils. We obtain roomtemperature GMI ratios [Z(0)-Z(Hs)]/Z(Hs) up to 800 % and GMR ratios [R(0)- R(Hs)]/R(Hs) up to 2400 % at frequencies of 100 kHz-10 MHz, with Hs the magnetic field where impedance and resistance saturate towards their minimum values. These high values are a direct consequence of the large dynamic relat

We engineer a semiconductor microcavity through an appropriate choice of geometry and materials in order to maximise the exciton-photon coupling. The polaritonic nonlinearities in such devices survive at high temperatures and high excitation densities. We measure parametric polariton amplification up to 220 K in CdTe microcavities and up to 120 K in GaAs ones. The amplification is also outstanding, reaching as much as 5000 at low temperature. The experimental observations suggest that the operating temperat

We report on efficient, narrow linewidth exciton recombination in GaAs/AlGaAs V-groove quantum wire light-emitting diodes at room temperature. The high efficiency is due to a selective carrier injection mechanism resulting in an estimated internal quantum efficiency of similar to 20% with an electroluminescence (EL) linewidth as narrow as 15 meV. The thermal broadening contribution to the linewidth is 6 meV due to exciton scattering with optical phonons. An analysis of the EL peak shift in a magnetic field

Using time-resolved photoluminescence, we have investigated the radiative behavior of neutral and negatively charged excitons in CdTe-based quantum wells. We find that the photoluminescence of negatively charged excitons can be well reproduced by a model of delocalized and thermalized three-particle complexes. A large radiative zone in k-space results from the transfer of the charged exciton momentum to the remaining electron (recoil effect). On the other hand, the photoluminescence decay of excitons is not

Magnetohydrodynamic (MHD) instabilities can limit the performance and degrade the confinement of tokamak plasmas. The Tokamak à Configuration Variable (TCV), unique for its capability to produce a variety of poloidal plasma shapes, has been used to analyse various instabilities and compare their behaviour with theoretical predictions. These instabilities are perturbations of the magnetic field which usually extend to the plasma edge where they can be detected with magnetic pick-up coils as magnetic fluctuat

We have performed spectral interferometry with Rayleigh scattered light coming from a single speckle and emitted after resonant creation of excitons in GaAs quantum wells:: The experiment confirms the coherence of the secondary emission at early times, regardless of sample:parameters. but underlines the stochastic nature of a single speckle. The scattered electric field is calculated, correctly accounting for the center-of-mass quantization in the disordered potential. We find that the amplitudes of the ele

Time-resolved measurements of the resonant Rayleigh scattering from quantum well excitons are shown to provide information on the energy-level statistics of the localized exciton states. The signal transients are reproduced by a microscopic quantum model of the exciton two-dimensional motion in presence of spatially correlated disorder. This model allows quantitative determination of the average energy separation between the localized states. Here this quantity turns out to be only a few times smaller than

Photoluminescence lifetimes of the n = 2 level in a large quantum well show a clear nonmonotonic dependence on the density of optically generated carriers. Varying the power density over five orders of magnitude we prove directly the high efficiency of carrier-carrier interaction for intersubband scattering when longitudinal-optical phonon emission is suppressed. For low densities, the observed n = 2 decay times get shorter (from 40 down to 5 ps) as the density is increased. At high densities Pauli blocking

The time-resolved secondary emission of resonantly created excitons in GaAs quantum wells is studied using femtosecond up-conversion spectroscopy. The behaviour of the rise and decay of the secondary emission and reflectivity in quantum welts is strongly dependent upon the disorder at the interfaces, the exciton density and the temperature. In the case of low densities and temperatures the emission is independent of the exciton density and rises quadratically in time, in excellent agreement with recent theo

We report on the optical response of a semiconductor microcavity featuring a strong exciton-photon coupling. The weak excitation regime is investigated experimentally by means of time-resolved transmission and four-wave mixing experiments. The influence of electronic disorder on the coherent exciton-photon dynamics is discussed in terms of tl-ie solutions of the Maxwell-Bloch equations. The high excitation regime is investigated by using transient sub-picosecond pump-probe experiments. Optical amplification

Dynamics of charged excitons in GaAs quantum wells under high magnetic field

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Level repulsion of exciton states in disordered semiconductor nanostructures

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