Specific features of the indirect exciton luminescence line in $\mathrm{GaAs}/{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ double quantum wells

A study is reported of the low temperature $(T<\mathrm{}30\mathrm{}\hspace{0.5em}\mathrm{K})$ photoluminescence from space-indirect excitons (IX) in $\mathrm{GaAs}/{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ double quantum wells at pumping density P and external electric field $V_{\mathrm{dc}}.$ At certain values of the external parameters $(P,\hspace{0.5em}T,$ and $V_{\mathrm{dc}})$ a part of the spectral profile of the IX line shows an enormous increase (shot) in photoluminescence intensity (three times), fluctuating with time on a characteristic scale of tens of seconds. This anomalous behavior is explained in terms of the theoretical model of the Bose-Einstein condensation occurring in a system of two-dimensional bosons that has, in addition to the extended (free) states, some discrete energy spectrum below the bottom of the free zone.