Observation of excitation transfer among neighboring quantum dots

Coupling between spatially separated zero-dimensional states has been observed in a system of self-assembled ${\mathrm{In}}_{0.55}{\mathrm{Al}}_{0.45}\mathrm{As}$ quantum dots. Photoluminescence excitation spectra, taken at 4.2 K with a near-field scanning optical microscope, reveals narrow resonances in the emission lines of individual dots when the excitation energy is tuned below the barrier band edge. A fraction of these resonances occur simultaneously in emission corresponding to different dots, evincing lateral interdot excitation transfer. Experiments show that the wetting layer in the sample consists solely of localized states which are then invoked to explain the excitation transfer over the relatively large interdot spacing.