M.V. Marquezini

Magnetically Enhanced Exciton-exciton Correlations In Semiconductors

We present investigations of fs time resolved coherent wave mixing under high magnetic field. Our experiments reveal a new regime at high magnetic field and low excitation density dominated by the Coulomb interaction. This regime is inconsistent with the semiconductor Bloch equations. A model which includes exciton-exciton correlation successfully describes many features of this regime. {copyright} {ital 1997} {ital The American Physical Society}

Quantum Confined Fano Interference

Quantum size effects have been thoroughly investigated since advances in material synthesis made possible the growth of semiconductor heterostructures with atomic monolayer accuracy. They become apparent in a physical phenomenon when at least one dimension of the sample becomes comparable to or smaller than the length scale that governs the quantum mechanics of that phenomenon. In the optical domain the exciton Bohr radius ao is usually the relevant length scale, and quantum confinement dominates the optical properties of semiconductor structures of size L # ao [1,2]. In the case of transport the carrier de Broglie wavelength lB determines the length scale at which quantum transport effects are observed [3]. In this Letter we present a new example of quantum size effects, apparent in the line shape of an optical resonance

Phase-amplitude spectroscopy of GaAs polariton

Summary form only given. In the absence of strong damping, the coupling between the GaAs exciton and the electromagnetic field leads to the creation of the exciton-polariton. The polariton dispersion curve has been studied by techniques such as resonant Brillouin scattering. But the longitudinal-transverse splitting (/spl Delta//sub LT/) being very small in GaAs, so far the polariton had not been observed directly in the linear absorption spectrum; the fundamental resonance remaining essentially exciton-like even in high quality samples. We present here the first direct observation of the polariton signature in both absorption and phase spectra of very high quality bulk GaAs. Our experimental findings are explained by a full solution of the Maxell/semiconductor Bloch equations (M-SBE), which in particular shows that /spl Delta//sub LT/, and the exciton damping /spl gamma/, cannot be read off in a simple way from the absorption (or phase) spectrum.

Phase spectroscopy in semiconductor structures

Summary form only given. We present applications of phase/amplitude spectroscopy in GaAs-based semiconductor structures, using Fourier Transform Spectral Interferometry. This technique allows one to measure both phase and amplitude of an optical pulse transmitted by the sample and therefore provides simultaneous absorption and refractive index measurement. We have used this approach to study how the optical response is affected by quantum confinement, temperature and external perturbations (e.g., magnetic field, optical excitation). We show here two studies of particular interest. First, the study of the dielectric function of a GaAs/AlGaAs multiple quantum well structure (MQWS) near the bandgap and at different temperatures. We show that it is possible to describe the complex dielectric function across the exciton resonances by analytical formulae assuming that the MQWS has a fractional dimension that translates the fact that real QWs are structures intermediate between the 3D unconfined bulk and ideal 2D systems. Second, the study of magnetically induced Fano-resonances (FR) in bulk GaAs under various excitation densities. They originate from a quantum interference between degenerate 1D continua and magnetoexcitons of different Landau levels coupled via Coulomb interaction. Using new analytical expressions describing this interference, we determine for the first time the collisional broadening of the continuum states.