Excitonic lattice control Customizing the refractive index of wells and barriers in a periodic array of quantum wells yields a way to controlthe reflectivity and dispersion of an excitonic lattice. The result is a new method for slowing or modulating light.

摘要

Light interacts strongly with matter in aquantum well (QW) when its frequencyis close to the resonance of an exciton —a quasiparticle composed of an electron inthe conduction band bound to a hole inthe valence band. This is an effect similarto the coherence that occurs between theexcited and ground states of an atom, whenthe atom is subjected to resonant excitation.This light-matter interaction becomesmuch stronger when the spacing betweenQWs arranged in a periodic array is exactlyhalf the exciton wavelength, because theexcitonic polarizations in the QWs are in phase and therefore interfere constructively;that is, the Bragg condition is satisfied. Thisexcitonic lattice (Fig. la) results in a highreflectivity around the exciton resonancewavelength, and can be used for the`switching' of light.