Electron-phonon quantum kinetics in the strong-coupling regime

Abstract

Summary form only given. While ultrafast semiconductor spectroscopy has investigated scattering times, i.e. the time between different scattering events, for many years, quantum kinetics asks for the duration of one scattering process, i.e. for the memory time. For the electron-LO-phonon quantum kinetics in the weak coupling regime (GaAs), quantum kinetics shows up as an oscillation in the coherent four-wave mixing (FWM) signal. This observation was interpreted as an oscillation of a band electron back and forth between its initial and a final state it scatters into (for long times) due to the emission of n=1 phonon. We discuss the strong electron-phonon coupling regime, in which n>1 phonon scattering processes are expected to become important as well. Bulk ZnSe is used as a model system, in which the Frohlich-constant is about one order of magnitude larger than in GaAs. In our experiments, the band edge of an antireflection-coated, 100 nm thin film of ZnSe at low temperatures is excited with blue, transform-limited 13 fs pulses. Two-pulse, three-pulse FWM-experiments and coherent control experiments are performed and discussed.