BLOCH WAVE-PACKETS IN SEMICONDUCTOR SUPERLATTICES - COMPOSITION AND SPATIAL DISPLACEMENT

We investigate the temporal and spatial displacement dynamics of optic ally excited wave packets in a semiconductor superlattice. We present an experimental technique which measures directly the displacement of the wave packet center-of-mass: the oscillating Bloch wave packets cre ate a microscopic dipole moment which carl be detected using tile shif t of the Wannier-Stark ladder transition energy as a sensitive field d etector. A true spatial oscillation of the photo-excited wave packet. identifies quantum beats of the Wannier-Stark states as: Bloch oscilla tions. We show that the Bloch wave packet undergoes harmonic spatial m otion in accordance with the predictions of Bloch and Zener. The influ ence of initial experimental conditions on evolution and composition o f tile wave packet is discussed.