Dipolar molecular fluids are very important and abundant in nature, and yet their complex collective microscopic ordering and correlations are still not well understood. Cold two-dimensional dipolar fluids are predicted to display a very rich phase diagram in both the classical and quantum regimes, far beyond the well studied weakly interacting gases, and are currently a major thrust in modern cold atoms and molecules research.

I will show an experimental evidence of two correlation regimes of a cold dipolar exciton fluid, created optically in a semiconductor bilayer heterostructure. In the higher temperature regime, the average interaction energy between the particles shows a surprising temperature dependence which is an evidence for correlations beyond the mean field model. At a lower temperature, there is a sharp increase in the interaction energy of optically active excitons, accompanied by a strong reduction in their apparent population. This is an evidence for a sharp macroscopic transition to a dark state as was suggested theoretically.