Off-branch polaritons and multiple scattering in semiconductor microcavities - art. no. 075311

Angle-resolved measurements show unexpected emission resonances of the pola ritons in a semiconductor microcavity. These resonances appear when more th an one in-plane polariton mode is macroscopically occupied. The new resonan ces observed in angle-resolved luminescence do not lie on the expected pola riton branches and possess different dispersion relations with negative eff ective mass. The experimental results can be well explained using an intera cting polariton model that treats multiple scattering. The k dispersion of the luminescence resonances is reproduced using the Bogolubov approximation that deals with the macroscopic coherence of the signal, pump, and idler m odes. This model also explains many puzzling features such as the stimulati on of resonant Rayleigh scattering in the backward direction. In addition, the use of nonresonant control beams for coherent control of the polaritons is shown both experimentally and theoretically. The rich complexity of new phenomena in optically excited semiconductor microcavities can be attribut ed to the distinctive anti-Hermitian or anomalous coupling between polarito ns.