Optical Nonlinearity Induced by Giant Dipole Moment of Wannier Excitons

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Abstract
A new mechanism for enhancing optical nonlinearities in quantum well structures, subject to an electric field normal to the layers, is investigated. It is found that large nonlinearities are induced by virtual transitions of Wannier excitons with "giant dipole moments." In contrast to other mechanisms, this enhancement mechanism is independent of correlations between excitons, for any order of nonlinearities. This fact results in a resonant enhancement at half the excitonic energy, and an ultrafast response, even faster than other virtual-process-induced mechanisms.