Quantum-kinetic dephasing in resonantly excited semiconductor quantum wells

We investigate resonant time-resolved four-wave mixing on GaAs quantum wells at $T=300\mathrm{}\mathrm{K}$ and at elevated carrier densities using excitation with 11 fs optical pulses. The experiments are compared with non-Markovian quantum-kinetic calculations including carrier-carrier and carrier-LO-phonon scattering. A self-consistently determined two-time-dependent screened random-phase approximation Coulomb potential is used for the carrier-carrier scattering. In experiment and theory we find an unusual real-time response, which is far from an ideal photon echo. Surprisingly, we also find that the dependence of the decay time τ of the four-wave-mixing signal versus the optically excited nonequilibrium electron-hole pair density $n_{\mathrm{eh}}$ is quantitatively similar to the corresponding behavior of bulk GaAs. Thus both data sets can be fitted by the same form ${\tau }^{-1}={\tau }_0^{-1}{+cn}_{\mathrm{eh}}^{1/3}.$ This is not consistent with previous experimental work in a more limited range of carrier densities, which determined different behavior for quasi-two-dimensional (2D) and 3D, i.e., exponents of 0.3 and $0.55\pm 0.04,$ respectively.