INFLUENCE OF LO-PHONON EMISSION ON BLOCH OSCILLATIONS IN SEMICONDUCTOR SUPERLATTICES

The intraband phase coherence of electronic Bloch wavepackets in semic onductor superlattices is partially conserved when electrons undergo e nergy relaxation by LO-phonon emission. The decay time of the intraban d coherence as probed by terahertz-emission spectroscopy is found to b e unaffected by excitation below or above the threshold for LO-phonon emission. On the other hand, the population relaxation probed by femto second optical transmission spectroscopy is drastically accelerated wh en 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.