Superfluidity of indirect excitons and biexcitons in coupled quantum wells and superlattices

• The collective properties of indirect excitons in coupled quantum wells (CQWs) are considered. The energy of the ground state of the exciton liquid as a function of the density of electrons a and holes h at different separations D between a and h layers is analysed. The quantum gas-liquid transition as D decreases is studied. The superfluidity appearance temperatures in the system (Kosterlitz-Thouless transition temperatures) have been estimated at different separations D between a and h layers. For the anisotropic two-dimensional e-h system in CQWs the Mott metal-insulator quantum transition is considered. The instability of the ground state of the system of interacting two-dimensional indirect excitons in a slab of superlattice with alternating a and h layers is established. The stable system of indirect quasi-two-dimensional biexcitons, consisting of indirect excitons with opposite directed dipole moments, is considered. The radius and the binding energy of the indirect biexciton are calculated. The collective spectrum of a rare system of two-dimensional indirect biexcitons, interacting as electrical quadrupoles, is studied. The density of the superfluid component n(s) (T) and the Kosterlitz-Thouless phase transition to the superfluid state in this system are analysed.

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