is tracked by imaging the photoluminescence (PL) emitted via exciton recombination along the SAW transport path. The laser excitation was focused onto a 5 $\mu$m (10 $\mu$m) spot on the top semitransparent electrode by a 10x (5x) microscope objective. The light emitted along the SAW transport channel was collected by the same objective, dispersed by a single grating spectrometer and imaged onto a cooled charge coupled device (CCD) camera with spatial resolution of 1 $\mu$m (2 $\mu$m).

Results {#Results}
=======

Acoustic exciton transport {#Acoustic_exciton_transport}
--------------------------

The two PL images superimposed on the device structure of Fig. \[Fig1\](a) compare the excitonic PL in the absence (left plot) and presence (right plot) of a SAW. While in the former the emission is restricted to the region near the excitation spot, the latter shows substantial PL at the edge of the STE located approx. 500 $\mu$m away from the laser spot. The remote PL is attributed to the recombination of IXs transported by the SAW at the edges of the STE, where the sudden reduction of the vertical field ${F_\mathrm{Z}}$ creates a potential barrier blocking the IX transport [@Ref12]. As the IXs are pushed by the SAW against this barrier their concentration increases 