Electro-optic investigation of the Coherent Hall Effect in semiconductor superlattices

After the first observation of the Coherent Hall Effect in a GaAs/Al(0.3)Ga(0.7)As superlattice by means of THz-emission spectroscopy, the dynamics of impulsively excited electron wavepackets in crossed electric and magnetic fields has now been investigated in more detail by reflective electro-optic sampling (REOS). In agreement with the predictions of a semiclassical model, the experiments show the existence of two strictly separated regimes of charge-carrier motion depending on the ratio E/B of applied electric and magnetic field. Both, the magneto-Bloch regime for dominating electric field and the cyclotron-like regime of motion for dominating magnetic field, exhibit a characteristic frequency dependence of the wavepacket oscillations on the external fields. The REOS measurements supplement our results achieved by THz-emission spectroscopy by covering a much larger range of experimental parameters because REOS is not affected by absorption by the cryostat windows of our set-up as is the THz radiation at frequencies above 2 THz, and the detection of high oscillation frequencies is possible.