Schedule Sep 10, 2002
Correlation Effects in the Coherent Optical Response of Semiconductors
Dr. Daniel Chemla, Berkeley
http://www.lbl.gov/msd/chemla/
Over the last decade a wealth of novel information on Coulomb correlation and electronic dynamics in semiconductors has been obtained in regimes where traditional assumptions fail. The usual description of solids assumes a quasi-stationary limit in which the Random Phase Approximation is valid. However, at low density and on a time-scale short compared to the time between quasi-particle collisions, not enough events happen over the time span of an experiment for a quasi-particle to interact witha substantial fraction of its neighbors. Thus it become possible to observed deviations from mean-field theory, a regime where the scattering fluctuations induce large fluctuations of the mean-field order parameters and high order correlations become dominant. Another regime where traditional assumptions fail is that of strongly correlated dynamics where it is no more justified to treat the interactions between quasi-particles as scattering events local in space and time, a key assumption of the Boltzmann theory. Recent coherent time resolved spectroscopy studies with time resolution much shorter than quasi-particle scattering time scales have revealed features related to genuine 4-particle and 6-particle correlations and memory effects in electron-electron interaction and electron-phonon interaction in semiconductors. In this conference I give a comprehensive and balanced account of recent advances, both experimental and theoretical, in our understanding of dynamical Coulomb correlations in semiconductors. I shall try to focus on the most important physics and, as much as possible, give an intuitive picture of the new phenomena that have been observed.

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