Quantum Kinetic Electron-Phonon Interaction in GaAs: Energy Nonconserving Scattering Events and Memory Effects

Abstract

Highly energetic electrons in GaAs emitting LO phonons are studied via femtosecond transmission spectroscopy. It is demonstrated for the first time that energy is not conserved on a time scale as short as a LO oscillation period: A replica of the initial distribution starts spectrally broadened before it sharpens into the excitation shape. This scenario is repeated for every step in the phonon cascade. Simulations combining an exact solution of quantum kinetics within a simplified model and a calculation of the polarization including Coulomb effects quantitatively agree with the data.