Dynamics of Bloch oscillations in semiconductor superlattices: direct determination of displacement

Abstract

We investigate the spatial displacement dynamics of optically excited wave packets in semiconductor superlattices. A short laser pulse exciting semiconductor superlattice induces quantum beats between different excitonic states that in turn leads to formation of a time-varying coherent wave packet. The real space oscillation of the excited wave packet identifies these quantum beats of the Wannier-Stark states as Bloch oscillations: We present an experimental technique which measures directly the displacement of the wave packet center-of-mass. The oscillating Bloch wave packets create a microscopic dipole moment which can be detected using the shift of the Wannier-Stark ladder transition energy as a sensitive field detector. We show that the Bloch wave packet undergoes harmonic spatial motion, Proing for the first time the predictions of Bloch and Zener. The influence of an experimental conditions on displacement of the Bloch wave packet is discussed.