Recent time-resolved differential transmission and Faraday rotation measurements of long-lived electron spin coherence in quantum wells displayed intriguing parametric dependencies. For their understanding we formulate a microscopic theory of the optical response of a gas of optically incoherent excitons whose constituent electrons retain spin coherence, under a weak magnetic field applied in the quantum well's plane. We define a spin beat susceptibility and evaluate it in linear order of the exciton density. Our results explain the many-body physics underlying the basic features observed in the experimental measurements.
@article{arxiv.0804.2418,
title = {Electron-spin beat susceptibility of excitons in semiconductor quantum wells},
author = {N H. Kwong and S. Schumacher and R. Binder},
journal= {arXiv preprint arXiv:0804.2418},
year = {2008}
}