Rice, W.D.Kono, J.Zybell, S.Winnerl, S.Bhattacharyya, J.Schneider, H.Helm, M.Ewers, B.Chernikov, A.Koch, M.Chatterjee, S.Khitrova, G.Gibbs, H.M.Schneebeli, L.Breddermann, B.Kira, M.Koch, S.W.2013-04-032013-04-032013Rice, W.D., Kono, J., Zybell, S., et al.. "Observation of Forbidden Exciton Transitions Mediated by Coulomb Interactions in Photoexcited Semiconductor Quantum Wells." <i>Physical Review Letters,</i> 110, (2013) American Physical Society: 137404. http://dx.doi.org/10.1103/PhysRevLett.110.137404.https://hdl.handle.net/1911/70890We 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 2s and 2p states, yielding an effective terahertz transition between the 1s and 2s populations.engArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.Journal articlehttp://dx.doi.org/10.1103/PhysRevLett.110.137404