Pushing Photons with Electrons: Observation of the Polariton Drag Effect

Exciton-polaritons are quasiparticles that are a superpositions of excitons and photons. In a microcavity, exciton-polaritons have an effective mass and can form a Bose-Einstein condensate (BEC). Experimentally, this condensate can be generated by pumping light into a microcavity structure with quantum wells at the antinodes of the light field. The features of the polaritons, such as energy, real-space, and momentum-space distributions, are carried by the light they emit, so we can measure those by using conventional optical methods.

In our experiment, we observed a change in the angle of emission of the photons when injecting electrons to the system, which indicates that the interaction of electrons with the polaritons changes the momentum of the polariton condensate. The condensate flow was accelerated when electrons flow with the same direction, while the condensate was slowed down when electrons flow in the opposite direction. Because the experiment is a photon-in, photon-out system, this is equivalent to steering photons using a DC electrical current. A theoretical model is also built to describe the effect.