Terahertz Excitations of Lambda Systems in a Semiconductor Microcavity

Recent experiment-theory investigations have demonstrated that the 2p-exciton state and the polariton resonances of a semiconductor quantum-well (QW) microcavity form a lambda (Lambda) system where a terahertz (THz) field can selectively couple to either of the transition-allowed arms. However, semiconductors are open systems because seemingly isolated states are coupled to the continuum of states, either directly or via Coulomb or phonon scattering. A systematic theory is presented to treat these effects in a Lambda system and in a two-level system (TLS) described by the 1s-to-2p exciton transition in a semiconductor QW, without the microcavity. Excitonic occupations of polarization are analyzed as function of THz-field frequency and intensity with (Lambda system) and without (TLS) cavity. Even though the existence of Lambda and TLS resonances is verified, significant deviations are observed at higher THz intensities, as higher ionized exciton states are generated via multi-THz-photon absorption. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim