Abstract

By shining light on a semiconductor, one creates pairs of electrons and holes that bind together with the Coulomb interaction to make a neutral ``atom’’ called an exciton—- the solid state analog of positronium. The possibility that a gas of excitons might undergo Bose-Einstein condensation was raised over 40 years ago.

Though no unequivocal demonstration of excitonic BEC has been given in traditional exciton systems, the phenomenon is related to new quantum phases that have been observed in quantum Hall bilayers, and some quantum spin systems, and quite possibly recently in exciton polaritons (which are a resonance between exciton and photon in a strongly coupled optical microcavity).

My talk will focus on explaining the basic ideas, reviewing the connections between different experimental systems, and discussing the most recent experiments on exciton polaritons.