Exciton Tunneling Revealed by Magnetically Tuned Interwell Coupling in Semiconductor Double Quantum Wells

We have found strong evidence for tunneling of excitons as an entity in CdTe/CdMnTe and CdTe/CdZnTe asymmetric double quantum wells (QWs). An external magnetic field changes the coupling between the two QWs by allowing resonances to occur between excitonic states. The tunneling dynamics are investigated by time-resolved and steady-state photoluminescence spectroscopies under magnetic field. Very efficient tunneling is found when the transfer of a spatially direct exciton is possible, either with the emission of LO phonons or via the resonance with the $2s$ state of the low energy QW.