Exciton and charge density wave formation in spatially separated electron–hole liquids

Abstract

We present a microscopic many-body calculation investigating the competition between the charge density wave and exciton formation in coupled electron–hole layer systems at finite temperature. We find that as the layer separation is decreased there is a divergence at a finite wave vector in the static susceptibility, indicating an instability in the liquid to a coupled charge density wave. We also see evidence in the pair correlation function g( r ) for the liquid phase of a divergence occurring at small r when the layer separation is reduced sufficiently, which would indicate the onset of a bound state instability. However, the charge density wave instability occurs in the liquid before g( r ) can actually diverge. The unified picture which starts to emerge from our results is of a charge density wave instability occurring in the liquid phase at a layer separation larger than the exciton radius. This leaves open the possibility of a second transition from the charge density wave state to the excitonic phase.