Bose-Einstein condensation of excitons: 50 years later, at last!
Institut des NanoSciences de Paris
Semiconductor excitons constitute model composite bosons made of two fermions, an electron and a hole bound by Coulomb attraction. The excitons bosonic character is therefore dominant in a dilute regime so that it was envisioned already 50 years ago that excitons undergo Bose-Einstein condensation under accessible experimental conditions.
This talk emphasises the experimental and theoretical barriers that have prevented the demonstration of exciton condensation, prior to our recent works. As predicted by Combescot et al, I will show that a condensate of excitons is made by a dominant fraction of lowest energy and optically inactive excitons, coherently coupled to a weak population of higher energy and optically bright ones. The latter part allows detecting quantum statistical signatures of the four-component condensate, such as macroscopic spatial coherence below a critical temperature of about 1 Kelvin. As expected, I will show that quantised vortices emerge in the quantum regime, unveiling a superfluid character. All together, our experiments reveal a novel type of quantum gas completing atomic systems, superconductors and liquid helium.