Investigation of Bloch oscillations in a GaAs/AlGaAs superlattice by spectrally resolved four-wave mixing.

We study Bloch oscillations (BO) in GaAs/AlGaAs superlattices with miniband widths of 19 and 38 meV at various lattice temperatures. In the time domain, we use transient degenerate four-wave mixing (FWM), while simultaneously monitoring the Wannier-Stark ladder (WSL) in the frequency domain by transmission spectroscopy. Spectrally resolved FWM measurements prove unambiguously that the oscillations in the decay of the FWM signal are due to quantum interference as expected for a wavepacket performing the BO.