Abstract
The instability of the ground state of a system of two-dimensional spatially indirect excitons interacting in a slab of superlattice with alternating electron and hole layers is established. The stable system of spatially indirect quasi–two-dimensional biexcitons, consisting in spatially indirect excitons with opposite directed dipole moments is considered. The radius and the binding energy of spatially indirect biexciton are calculated. The collective spectrum of a low-density system of two-dimensional spatially indirect biexcitons, interacting as electrical quadrupoles, is studied. The density of the superfluid component ns(T) and the Kosterlitz-Thouless phase transition to the superfluid state in this system are analyzed.
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