We have previously demonstrated that the indirect excitons (IXs) in quantum well structures can be efficiently transported by SAWs using the GaAs double quantum well (DQW) structure illustrated in Fig. 1(a). Here, IXs excited by a focused laser beam are captured and transported by the moving band-gap modulation produced by the SAW strain. Transport is detected by recording the photoluminescence (PL) induced by IX recombination along the SAW path, as shown by the PL image superimposed on the sample sketch.
The dynamics of the acoustic transport was studied by recording time-dependent PL profiles at different distances d from the pulsed laser excitation spot (Fig. 1(b)). This figure shows well-defined PL pulses with time delays τ (relative to the laser pulse) increasing with propagation distance according to τ = d /vIX, where vIX is the average IX transport velocity. The rising edge of the time-resolved PL pulses becomes less abrupt for increasing d while the trailing edge develops a tail indicating a distribution of arrival times at the detection position. The latter is attributed to the trapping and subsequent release of IX by defects along the path, which increase their propagation time. The dashed lines superimposed on the data were obtained for a model for the trapping dynamics, which reproduces very well the measured data.
The present studies show that the IXs are carried as well-defined packets, which can be synchronized with pulsed photon beam and approximately keep their shape while moving over long distances with the SAW velocity.