left inset). In both cases, the IXs were driven by a SAW generated using P$_{RF}$=2 dBm. The filled circles mark the position of the laser excitation spot. (d) Spatially resolved $\Delta$I$_{PL}$ profiles along the transport channel in the ON (red curve) and OFF (blue curve) states. (e) and (f) display the corresponding time-averaged PL profiles calculated by a numerical model (see text). The overlays indicate the positions of drain, gate and source electrodes.[]{data-label="EXAT"}](Figure_2.png){width="\columnwidth"}

The switching action of the EXAT is demonstrated by the differential PL ($\Delta$I$_{PL}$) images in Figs. \[EXAT\](b) and \[EXAT\](c). These images display the changes induced by the SAW and were obtained by subtracting PL images recorded in the presence and absence of the acoustic excitation. In both cases, excitons were optically excited on D, which was kept at the same bias voltage as S (V$_{S}$=V$_{D}$=-1.4 V). Note that the negative $\Delta$I$_{PL}$ values around the excitation spot are due to the IX extraction by the SAW and their transport along the SAW propagation direction. In the ON state (Fig. 2(b)), IXs can be easily transferred from D to S by applying a gate voltage V$_{G}$=V$_{S}$=V$_{D}$ (cf. right inset of Fig. \[EXAT\](b)). The fringe electric field at the edges 