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Possibility of an excitonic ground state in quantum wells.

The possibility of the formation of an excitonic insulator in semiconductors with an indirect gap smaller than the exciton binding energy has been considered in the past. The advent of quantum-well structures makes it feasible to consider indirect gaps in real space that can be conveniently tuned through the semiconductor-semimetal transition. We discuss various quantum-well configurations where a spontaneous condensation of excitons into a collective ground state may be possible.