Direct and indirect exciton mixture in double quantum wells

The exciton system in double quantum wells is considered under the condition that the ground state is the spatially indirect exciton. At high pumping the growth of the exciton concentration can lead to such a significant increase of the indirect exciton energy that it becomes equal to the direct exciton energy. Then further increase of pumping leads to the formation of a mixed direct-indirect exciton phase. A rough estimate of the exciton energy in the mixed phase explains puzzling features of some recent exciton measurements. An experiment that would reveal the main characteristic features of the mixed phase is suggested