Stability of indirect biexcitons in superlattices

The unstability of the ground state of the system of interacting two-dimensional indirect excitons in a slab of superlattice with alternating electron and hole layers is established. The stable system of indirect quasi-two-dimensional biexcitons, consisting from indirect excitons with opposite directed dipole moments is considered. The radius and the binding energy of indirect biexciton are calculated. Collective spectrum of low-density system of two-dimensional indirect biexcitons, interacting as electrical quadrupoles, is derived. The density of superfluid component ns(T) and the temperature of the Kosterlitz–Thouless phase transition to the superfluid state in this system are obtained. We assume there are no external fields applied to the slab of superlattice under consideration.