Observation of Coulomb-Assisted Dipole-Forbidden Intraexciton Transitions in Semiconductors

W. D. Rice, J. Kono, S. Zybell, S. Winnerl, J. Bhattacharyya, H. Schneider, M. Helm, B. Ewers, A. Chernikov, M. Koch, S. Chatterjee, G. Khitrova, H. M. Gibbs, L. Schneebeli, B. Breddermann, M. Kira, S. W. Koch

Published 2012-03-18, updated 2012-12-05Version 2

We use terahertz pulses to induce resonant transitions between the eigenstates of optically generated exciton populations in a high-quality semiconductor quantum-well sample. Monitoring the excitonic photoluminescence, we observe transient quenching of the $1s$ exciton emission, which we attribute to the terahertz-induced $1s$-to-$2p$ excitation. Simultaneously, a pronounced enhancement of the $2s$-exciton emission is observed, despite the $1s$-to-$2s$ transition being dipole forbidden. A microscopic many-body theory explains the experimental observations as a Coulomb-scattering mixing of the 2$s$ and 2$p$ states, yielding an effective terahertz transition between the 1$s$ and 2$s$ populations.