Theory of coherent effects in semiconductors

A microscopic theory is applied to discuss coherent excitation effects in s emiconductors. The theory is evaluated to analyze ultrafast absorption chan ges around the exciton resonance in semiconductor quantum-well structures w here the relative strength of the different many-body contributions can be manipulated by proper selection of pump and probe polarizations. For two-ba nd systems and oppositely circular polarization it is shown that Coulombic correlation dynamics dominates the optical response. As a consequence, the optical Stark effect in this configuration corresponds to a red shift of th e exciton resonance in striking contrast to the usual atomic-like blue shif t. The predictions are confirmed by experiments using high-quality InGaAs q uantum-well systems. (C) 1999 Elsevier Science B.V. All rights reserved.