Anomalous Interlayer Exciton Diffusion in Twist-Angle-Dependent Moir\'e Potentials of WS2-WSe2 Heterobilayers
Abstract
The nanoscale periodic potentials introduced by moir\'e patterns in semiconducting van der Waals (vdW) heterostructures provide a new platform for designing exciton superlattices. To realize these applications, a thorough understanding of the localization and delocalization of interlayer excitons in the moir\'e potentials is necessary. Here, we investigated interlayer exciton dynamics and transport modulated by the moir\'e potentials in WS2-WSe2 heterobilayers in time, space, and momentum domains using transient absorption microscopy combined with first-principles calculations. Experimental results verified the theoretical prediction of energetically favorable K-Q interlayer excitons and unraveled exciton-population dynamics that was controlled by the twist-angle-dependent energy difference between the K-Q and K-K excitons. Spatially- and temporally-resolved exciton-population imaging directly visualizes exciton localization by twist-angle-dependent moir\'e potentials of ~100 meV. Exciton transport deviates significantly from normal diffusion due to the interplay between the moir\'e potentials and strong many-body interactions, leading to exciton-density- and twist-angle-dependent diffusion length. These results have important implications for designing vdW heterostructures for exciton and spin transport as well as for quantum communication applications.
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