Manifestation of collective properties of spatially indirect excitons in GaAs/AlGaAs asymmetric double quantum wells

Low-temperature (T = 1.8, 4.2 K) luminescence of GaAs/Al0.3Ga0.7As double-c oupled asymmetric quantum wells (DQW) is observed under variation of an ele ctric field V-dc applied along the normal to the DQW plane. The FWHM of the indirect exciton (IX) emission line was found to undergo, within a certain interval of V-dc, a strong (up to a factor 3.5) narrowing, accompanied by anomalously large IX intensity fluctuations in time within the V-dc region where a strong decrease (or increase) of the FWHM is observed to occur. The dependence of the FWHM on the pumping level I-p also exhibits a substantia l decrease of the FWHM within a certain I-p interval. The results obtained are discussed in the frame of an assumption which relates the observed phen omena to the onset of a condensed state in the interacting ensemble of spat ially indirect excitons in DQWs. (C) 1999 American Institute of Physics. [S 1063-7834(99)02602-7].