Pump-energy dependence of usual and unusual Bloch oscillations in a GaAs/AlAs superlattice

We have systematically investigated the wave-packet dynamics of Bloch oscillations (BOs) from the viewpoint of the characteristics of the Wannier-Stark (WS) localization states in a GaAs (6.8 nm)/AlAs (0.9 nm) superlattice embedded in a p-i-n diode structure, The coherent oscillations were detected with a reflection-type pump-probe technique. It is clearly confirmed that the unusual BO with the frequency of 2eFD/h occurs in a weak localization regime in addition to the usual BO with eFD/h in a strong localization regime, where F is the applied electric field, and D is the superlattice period. The systematic results of the pump-probe measurements as a function of pump energy indicate that the intensity of the unusual BO is drastically changed with pump energy, while a gradual change of that of the usual BO is observed, These results demonstrate that the quantum interference leading to the usual BO with 2eFD/h is much sensitive to the pump energy compared with that of the usual BO. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim