Role of the exchange of carriers in elastic exciton-exciton scattering in quantum wells

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We present detailed analysis of inter- and intraband transitions in GaN/AlN self-organized quantum dots grown on sapphire, silicon (111) and 6H-SiC substrates. Samples containing quantum dots of different size were characterized by means of transmission electron microscopy, photoluminescence and photoinduced absorption spectroscopy. Interlevel transitions in the conduction band were identified in the 0.52-0.98 eV range covering the telecommunication wavelength band. The s-p(z), transition ranges from 0.52 e

A new expt. allows the identification of residues that feature slow conformational exchange in macromols. Rotations about dihedral angles that are slower than the global correlation time tc cause a modulation of the isotropic chem. shifts of the nuclei. If these fluctuations are correlated they induce a differential line broadening between three-spin single-quantum and triple-quantum coherences involving three nuclei such as the carbonyl C', the neighboring amide nitrogen N and the amide proton HN belonging

The aim of this thesis work is to study the spin-dependent transport in multiwalled carbon nanotubes (MWNT). To do so, the electrical resistance of MWNT contacted between ferromagnetic electrodes has been measured, as a function of the contacts magnetic configuration and temperature. An original sample fabrication process to contact MWNT has been developed. The MWNT growth is achieved via chemical vapour deposition in the pores of an alumina template, with electrodeposited nickel or cobalt nanowires as cata

We have studied systems of asymmetric coupled GaAs V-groove quantum wires p-i-n diodes, in which the electrons and holes are injected into different wires. Despite the use of a 7 nm thick AlGaAs tunnel barrier, and although we demonstrate that holes tunnel more slowly than electrons, we observe a very efficient and fast tunneling between the quantum wires (QWR's). We attribute this to the achievement of a resonance between hole levels in the two QWR's. Photoluminescence excitation experiments are compared w

We discuss the spectral signatures of strong electronic correlations and electron-phonon interactions in two representative low-dimensional systems. In the 2D compound 1T-TaSe2 a charge-density-wave (CDW) induces a narrowing of the conduction band, which triggers a surface metal-insulator (M-I) transition and the disappearance of the quasiparticle (QP) features. In the 1D blue bronze K0.3MoO3 strong interaction with the lattice lead to pseudogapped polaronic lineshapes, and the large mass renormalization ma

We analyze the magnitude of degenerate two-photon gain of several quantum wells (QWs) in a resonant microcavity which is pumped off-resonantly by an optical field. A set of coupled phenomenological rate equations for electron-hole pairs and photons is derived. In the framework of this model, we make a realistic prediction of the time-integrated two-photon gain and find that a lambda-cavity containing 11 QWs would give a maximal amplification of similar to 2.3% for a peak,intensity of similar to 80 MW/cm(2).

We performed angle-resolved photoelectron spectroscopy (ARPES) and resistivity measurements on the layered metal 1T-TiTe2. We determined the quasiparticle dispersion and lifetime. In particular, we could characterize and separately evaluate the effects of the electron-electron and electron-phonon interactions on the experimental spectra. The good correlation between transport and spectroscopic scattering rates indicates that this material behaves as a model Fermi liquid system.

Crystal damage induced by irradiation is investigated using transmission electron microscopy (TEM) coupled to molecular dynamics (MD) calculations. The displacement cascades are simulated for energies ranging from 10 to 50 keV in Al, Ni and Cu and for times of up to a few tens of picoseconds. Samples are then used to perform simulations of the TEM images that one could observe experimentally. Diffraction contrast is simulated using a method based on the multislice technique. It appears that the cascade indu

The nonequilibrium dynamics of a two-dimensional electron-hole gas is studied in the regime of strong and resonant pumping of the exciton resonance. The Coulomb collision rates are consistently determined by taking into account the light-induced coherence of the two-band system that leads to a dressing of the carrier spectral functions. The light dressing dramatically reduces the Coulomb scattering efficiency. Results are presented for Rabi oscillations in the time domain and dynamical Stark splitting in th

Ultrafast pump-probe measurements evidence the dynamical Stark splitting in the exciton absorption spectrum of a single semiconductor quantum well. The intensity of the Stark sidebands in the spectrum is comparable to the linear absorption and their separation scales as the pump field amplitude. In the time domain the Rabi oscillations are observed. The semiconductor Bloch equations solved in the Hartree-Fock approximation demonstrate that the coherent exciton-light coupling dominates over the many-body dep

We consider an electron-phonon system in two and three dimensions on square, hexagonal, and cubic lattices. The model is a modification of the standard Holstein model where the optical branch is appropriately curved in order to have a reflection positive Hamiltonian. Using infrared bounds together with a recent result on the coexistence of long-range order for electron and phonon fields, we prove that, at sufficiently low temperatures and sufficiently strong electron-phonon coupling, there is a Peierls inst

A review is given of the math. foundations of av. Liouvillian theory and examples are provided of av. Liouvillian expressions derived for sequences in NMR which possess temporal symmetry or antisymmetry. The utility of this approach is demonstrated in the design of pulse sequences to measure the effect of cross-correlation between chem. shift anisotropy and dipolar couplings on relaxation rates in biomols. Exptl. verification of the theory is carried out on a 15N labeled sample of ubiquitin. [on SciFinder (

Role of the exchange of carriers in elastic exciton-exciton scattering in quantum wells

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Spectroscopy of the electron states in self-organized GaN/AlN quantum dots

Triple Quantum Decoherence under Multiple Refocusing: Slow Correlated Chemical Shift Modulations of C' and N Nuclei in Proteins

Longueur de diffusion de spin et magnétisme de structures nanotubes de carbone / matériaux ferromagnétiques

Electroluminescence and photoluminescence excitation study of asymmetric coupled GaAs/AlxGa1-xAs V-groove quantum wires

Strong electron-electron and electron-phonon interactions in one- and two-dimensional solids

Feasibility study for degenerate-two-photon gain in a semiconductor microcavity

Quasiparticle scattering processes in a model Fermi liquid: 1T-TiTe2

Correlation of simulated TEM images with irradiation induced damage

Strongly driven exciton resonances in quantum wells: Light-induced dressing versus Coulomb scattering

Direct observation of the excitonic ac Stark splitting in a quantum well

Charge density wave and quantum fluctuations in a molecular crystal

Average Liouvillian theory revisited: cross-correlated relaxation between chemical shift anisotropy and dipolar couplings in the rotating frame in nuclear magnetic resonance