Phase transitions in a system of two coupled quantum wells

It is predicted that an excitonic liquid is formed in a system of spatially separated electrons (e) and holes (h) in a system of two coupled quantum wells. The ground-state energy and the equilibrium density of the excitonic liquid are calculated as a function of the distance D between the wells. A gas-liquid quantum transition with increasing D is studied. The Berezinskii-Kosterlitz-Thouless transition temperatures at which superfluidity appears in the system are found (for different D). A quantum Mott metal-insulator transition in an anisotropic double-quantum-well structure is investigated. The region of existence of crystalline order in a system of spatially separated e and h is studied. Possible experimental manifestations of the predicted effects are discussed. (C) 1996 American Institute of Physics.