EXCITON AND CHARGE-DENSITY-WAVE FORMATION IN SPATIALLY SEPARATED ELECTRON-HOLE LIQUIDS

We present a microscopic many-body calculation investigating the compe tition between the charge density wave and exciton formation in couple d electron-hole layer systems at finite temperature. We find that as t he layer separation is decreased there is a divergence at a finite wav e vector in the static susceptibility, indicating an instability in th e 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 o ccurring 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 l iquid phase at a layer separation larger than the exciton radius. This leaves open the possibility of a second transition from the charge de nsity wave state to the excitonic phase. (C) 1998 Elsevier Science B.V . All rights reserved.