Microscopic theory of optical dephasing in semiconductors

Dephasing, i.e. the decay of the optical interband polarization in a semico nductor results from destructive interference effects between different mic roscopic contributions. For a system without ally disorder it is shown that the many-body Coulomb correlations lead to excitation-induced dephasing wh ich becomes increasingly important at elevated excitation levels. The effec t of disorder-induced dephasing is analyzed for low excitation levels, wher e the combined influence of excitonic, biexcitonic, and disorder scattering contributions lead to a temporal decay of the four-wave-mixing signal.