Photon echoes from semiconductor band-to-band continuum transitions in the regime of Coulomb quantum kinetics

We show that the coherent response of semiconductor band-to-band continuum transitions at room temperature, excited by 11 fs pulses at elevated carrier densities, deviates substantially from that expected for an ideal photon echo. A microscopic non-Markovian quantum kinetic theory of both electron-electron and electron-LO-phonon scattering reproduces these unusual experimental observations qualitatively and, furthermore, the famous scaling of the decay time tau with carrier density n(eh) according to tau-1 = tau(0)(-1) + cn(eh)(1/3) quantitatively. tau, however, cannot be associated with a single unique phase relaxation time T-2.