Influence of LO-phonon emission on bloch oscillations in semiconductor superlattices

The intraband phase coherence of electronic Bloch wavepackets in semiconductor superlattices is partially conserved when electrons undergo energy relaxation by LO-phonon emission. The decay time of the intraband coherence as probed by terahertz-emission spectroscopy is found to be unaffected by excitation below or above the threshold for LO-phonon emission. On the other hand, the population relaxation probed by femtosecond optical transmission spectroscope is drastically accelerated when the threshold is reached. Electrons which have undergone LO-phonon emission form a more localized distribution in k-space giving rise to a stronger THz signal.