PHASE-TRANSITIONS IN A SYSTEM OF SPATIALLY SEPARATED ELECTRONS AND HOLES

The formation of a superfluid exciton liquid in a system of spatially separated electrons and holes in a system of two coupled quantum wells is predicted and its properties are investigated. The ground-state en ergy and the equilibrium density of the exciton liquid are calculated as functions of distance D between the quantum wells. The properties o f a rarefied exciton gas with dipole-dipole repulsions are considered, where this gas is the metastable phase for D<1.9a and the stable pha se for D>1.9a (a* is the radius of the two-dimensional exciton). The gas-liquid quantum transition is examined for increasing D. The Berezi nskii-Kosterlitz-Thouless transition temperatures, at which superfluid ity arises in the system, are found for different values of D. Possibl e experimental manifestations of the predicted effects are discussed. (C) 1997 American Institute of Physics.