BLOCH OSCILLATIONS OF EXCITONIC WAVE-PACKETS IN SEMICONDUCTOR SUPERLATTICES

We present a detailed investigation of the coherent dynamics of excito nic wave packets composed of heavy/light-hole, electron miniband, and Wannier-Stark states in GaAs/AlxGa1-xAs superlattices. Using transient degenerate four-wave mixing, we study the dependence of Bloch oscilla tions and heavy/light-hole beats on the applied field, miniband width, lattice temperature, and excitation conditions. Bloch oscillations ar e observed in samples with minibandwidths varying from 13 to 46 meV an d at lattice temperatures up to 200 K. Under certain excitation condit ions, we observe higher harmonics of the Bloch oscillation frequency. Spectrally resolved transient four-wave mixing experiments show unambi guously that quantum-mechanical interference is the origin of the osci llations. The experimental four-wave mixing traces are compared with a theoretical model based on many-level third-order density-matrix theo ry.