The Gas Liquid Transition of Excitons

In this talk I shall review our work on the gas-liquid transition of 2D excitons in GaAs quantum wells. Below a critical temperature and above a critical density this system undergoes a phase transition to a liquid state. By employing a variety of optical spectroscopy tools we map the phase diagram of the system and show that the liquid is a Bose Einstein condensate. We find that the excitons condense in the lowest energy state which is not coupled to light (“dark excitons”).