Quantum interference currents by excitation of heavy- and light-hole excitons in GaAs/Al0.3Ga0.7As quantum wells

In this paper we report on the observation of quantum interference currents caused by the excitation of excitons with circularly polarized 150 fs laser pulses at room temperature in GaAs/Al0.3Ga0.7As quantum wells. The quantum interference currents were detected via free-space terahertz experiments. The importance of the excitonic contribution to the excitation process was revealed by the observation of a phase shift of the current when the excitation photon energy was tuned from the heavy-hole to the light-hole exciton absorption. We attribute the observed phase shift to a current reversal resulting from optical selection rules for circularly polarized light.