Resonant Rayleigh Scattering of Exciton-Polaritons in Multiple Quantum Wells

Materials Science and Engineering: B, 2001

ABSTRACT

physica status solidi (a), 2002

A novel semi-classical theory of exciton-polaritons in quantum wells (QWs) is presented. Timeresolved coherent optical spectra of QWs are described by the light coupling with ensembles of localized quantum dot-like exciton states. The ratio between reflection and resonant Rayleigh scattering (RRS) intensity gives a direct measure of the density of these excitonic dots. Good agreement with experimental data for time-resolved angle-dependent reflection and RRS from a GaAs single QW is achieved.

PHYSICAL REVIEW B, 2003

The resonant Rayleigh scattering dynamics of excitons in single GaAs quantum wells is investigated. The deviation of the measured intensity from the ideal ensemble average is analyzed as a function of the speckle ensemble size. The influence of the amplitude and correlation length of the exciton disorder potential is traced using a series of samples with varying inhomogeneous broadening and interface island sizes. The experimental data are compared with theoretical predictions using exciton states of spatially uncorrelated energies, as well as full calculations of the exciton polarization dynamics using a more realistic disorder potential including the formation of monolayer islands. Deviations from the dynamics of uncorrelated states are found at early times after excitation. They are reproduced by the calculations possessing a state correlation due to quantum mechanical level repulsion and a finite correlation length for the disorder potential. Additionally, the presence of a long-range disorder potential in the micrometer range is suggested. Changing the disorder potential by varying the island size influences the observed dynamics systematically according to the different disorder correlation lengths.

Physical Review B

We report investigations of highly resolved resonant Rayleigh scattering spectra from high quality GaAs quantum wells which were excited by a cw Ti:sapphire laser. Nevertheless, the resulting spectra show features of inhomogeneous broadening, such as resonance shifting and resonance fluorescence narrowing, arising from non-negligible localization of the excitons. Furthermore, the excitonic excitation dipoles were found to be preferentially aligned along ͑110͒ crystal axes. As a result, the Rayleigh component of the secondary emission does not necessarily reflect the polarization characteristics of the exciting laser.

Physical Review B, 2014

We present theoretical and experimental study of resonant Brillouin scattering of excitonic polaritons in one-dimensional multiple-quantum-well structure. We obtain general analytical results for the scattering light spectra, valid for arbitrary quantum well arrangement. Application of our theory to the specific case of short-period superlattice shows a perfect quantitative agreement with experimental results for the height, width and position of the Brillouin scattering peaks and allows us to determine the energy, radiative and nonradiative decay rates of quantum well excitons. We reveal the signatures of excitonic polariton formation in the scattering spectra and show, that the spectral width and height are strongly sensitive to the number of wells in the sample.

Physical Review Letters, 2002

A clear signature of enhanced backscattering of excitons is observed in the directional resonant Rayleigh scattering of light from localized two-dimensional excitons in disordered quantum wells. Its spectral dependence and time dynamics are measured and theoretically predicted in a quantitative way. The intensity enhancement has a large momentum span extending beyond the external light emission cone. This is a consequence of the small localization length of the exciton as a massive particle probed close to the band bottom. The localization length can be controlled by the photon kinetic energy. This constitutes a qualitative difference to backscattering phenomena in other branches of physics.

Physical Review Letters, 1999

We develop and experimentally verify novel Monte Carlo simulations of ultrafast resonant Rayleigh scattering from quantum well excitons. In contrast to existing theories, these simulations can study the dynamics and spectrum of resonant Rayleigh scattering from a single realization of disorder, and allow direct comparison to experimental data. We find excellent agreement between our experiments and simulations. Our studies demonstrate the high sensitivity of scattering dynamics to a particular realization of disorder, and provide new insights into the nature of spatial correlations of excitons.

Revue de Physique Appliquée, 1987

Physical Review B, 1998

We show numerically that spatial delocalization of excition-polariton states in multiple quantum wells leads to efficient narrowing of exciton resonances with respect to the single-quantum-well ͑QW͒ case. This is a manifestation of a motional narrowing effect, i.e., averaging of short-range potential fluctuations by extended exciton-polariton modes. Increasing the number of QW's or decreasing the degree of disorder, one recovers the superradiance regime where the exciton linewidth is governed by the splitting between the strongest excitonpolariton modes and now increases with an increasing number of QW's. Vertical disorder, in which the different wells are no longer equivalent, suppresses both effects. ͓S0163-1829͑98͒50720-5͔

Physica B: Condensed Matter, 1999

A dramatic suppression of the absorption of light by exciton polaritons is observed after resonant excitation of the polaritonic modes in a multiple quantum well Bragg structure. Time-resolved reflectivity measurements confirm that this is due to the formation of a dominant superradiant polariton mode created by the light-induced coupling of excitons in different quantum wells that suppress absorption. The stability of the superradiant mode is demonstrated at high excitation powers and at temperatures of up to 180 K.