Electron-Hole Liquid in the Couple Quantum Wells
  It is shown that the homogeneous state of the spatially separated electrons and holes in the coupled quantum wells (CQW) is instable if the layer charge density is smaller than the critical value specified by the parameters of the CQW. The effect is due to the many-body Coulomb correlations which provide the positive compressibility. The instability results in the formation of the inhomogeneous system which comprises the liquid electron-hole drops. 
V.S. Babichenko, I.Ya. Polishchuk, A.I. Pavlov, A. Guseynov and M.I.   Gozman
cond-mat.mes-hall