Phason-assisted interlayer exciton diffusion in a WSe2/WS2 moiré superlattice

The moiré potential arising from the relative twist and lattice mismatch in heterobilayers of two-dimensional materials has led to the discovery of novel excitonic species. Twist-angle dependent transport measurements of these interlayer excitons have been reported for WSe2/WS2 heterobilayers [1]. In our experiment, we use time- and spatially resolved spectroscopies to investigate the temperature dependent lifetime and diffusion length of various interlayer excitons in WSe2/WS2 heterobilayers, where the individual monolayers have been aligned to produce long-range moiré superlattices. We observe that the temperature dependent formation of the interlayer exciton is reflected in the overall lifetime and diffusion lengths of exciton species in the WSe2/WS2 heterobilayer. The excitons diffusion is affected by the presence of the moiré trap and increasing the temperature, they acquire enough energy to escape the potential barrier. However, at low temperature the moiré phonons (phasons) allow for non-zero diffusion of the exciton providing enough energy for the exciton to hop from one site to another.