Carrier-carrier scattering versus coherence in highly laser-excited semiconductors

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Abstract
For bulk GaAs as representative material we estimate the possibility of experimentally detecting oscillatory coherence effects in the transient nonlinear pump-and-probe absorption spectroscopy of semiconductors involving highly energetic and dense photo-excited electron- hole plasmas. Under such high-excitation conditions coherence effects in the nonlinear optical response are very difficult to observe because the carrier dynamic is strongly dominated by phase-breaking scattering processes, and here predominantly by carrier-carrier scatterings. Our theoretical framework consists of a hybridization of the quantum-mechanical equations of motion for the two-particle density matrix in k space with an ensemble-Monte-Carlo simulation of the single-particle scattering dynamics. Within the well-established Markov approximation this allows us to consistently obtain the leading scattering contributions to the electron-hole amplitude and thereby to the induced polarization and to the nonlinear optical susceptibility. For pump-and-probe absorption spectroscopy we propose, in terms of the excitation density and energy and of the temporal widths of the pump and the probe pulse, realizable experimental scenarios as candidates for detectable `Rabi'-type oscillatory coherence effects in the transient absorption change (bleaching) at the excitation frequency.

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