Electrostatic Conveyer for Excitons

We report on the study of indirect excitons in moving lattices—conveyers created by a set of ac voltages applied to the electrodes on the sample surface. The wavelength of this moving lattice is set by the electrode periodicity, the amplitude is controlled by the applied voltage, and the velocity is controlled by the ac frequency. We found the dynamical localization-delocalization transition for excitons in the conveyers and determined its dependence on exciton density and conveyer amplitude and velocity.

Figure 1

(a) CQW band diagram. $e$, electron; $h$, hole. (b) Electrode pattern, contacts are shown by circles. (c)–(f) $x\mathrm{\text{−}}y$ and $x$-energy PL images for conveyer off and on. (g),(h) PL intensity profiles $I(x)$. $P_{\mathrm{ex}}=20\mu \mathrm{W}$, $A_{\mathrm{conv}}=7.5\mathrm{meV}$, $v_{\mathrm{conv}}=0.7\mu \mathrm{m}/\mathrm{ns}$.

Figure 2

(a) The average transport distance of indirect excitons via conveyer $M_1$ as a function of the conveyer amplitude, $A_{\mathrm{conv}}$. Lines are a guide to the eye, $A_{\mathrm{turn}\mathrm{\text{−}}\mathrm{on}}$ is $A_{\mathrm{conv}}$ at the line intersection. (b) The measured (points) and calculated (triangles) $A_{\mathrm{turn}\mathrm{\text{−}}\mathrm{on}}$ versus the conveyer velocity. $P_{\mathrm{ex}}=20\mu \mathrm{W}$.

Figure 3

(a) The measured and (b) calculated average transport distance of indirect excitons via conveyer $M_1$ as a function of density. $A_{\mathrm{conv}}=4.9\mathrm{meV}$, $v_{\mathrm{conv}}=0.7\mu \mathrm{m}/\mathrm{ns}$.

Figure 4

Theoretical simulations. A snapshot of (a) the conveyer potential [gray (green) curve], (b) exciton density distribution [gray (red) curve], and (a) corresponding screened conveyer potential [black (blue) curve]. (b) PL intensity (black curve). $A_{\mathrm{conv}}=8\mathrm{meV}$, $v_{\mathrm{conv}}=0.7\mu \mathrm{m}/\mathrm{ns}$. (c) $M_1$ vs $A_{\mathrm{conv}}$. $D_x^{(0)}=30{\mathrm{cm}}^2{\mathrm{s}}^{-1}$, $\Lambda ={10}^9{\mathrm{cm}}^{-2}{\mathrm{ns}}^{-1}$, ${\tau }_{\mathrm{opt}}=50\mathrm{ns}$.