Spatio-temporal Bloch oscillations in GaAs/AlGaAs superlattices

Zener [1] has predicted that an electron in a periodic potential and static electric field will perform harmonic Bloch oscillation (BO) in real space. Here results, which directly prove the existence of this spatial oscillation, are presented. By observing the periodical shift of the Wannier-Stark levels, the macroscopic dipole moment associated with the Bloch oscillations of the electron wave packet can be traced. The displacement of the electron wave packet can then be derived as a function of time. The dependence of Bloch oscillation dynamics on the optical excitation conditions is discussed. In particular, continuous transition between the electron center-of-mass harmonic spatial motion and a symmetric breathing-mode motion without macroscopic dipole oscillation is demonstrated. Influence of excitonic effects due to the interaction with photoexcited holes on the wave packet dynamics is shown.