Anomalous Interlayer Exciton Diffusion in WS2/WSe2 Moire Heterostructure

A Rossi and J Zipfel and I Maity and M Lorenzon and M Dandu and E Barré and L Francaviglia and EC Regan and ZC Zhang and JH Nie and ES Barnard and K Watanabe and T Taniguchi and E Rotenberg and F Wang and J Lischner and A Raja and A Weber-Bargioni, ACS NANO, 18, 18202-18210 (2024).

DOI: 10.1021/acsnano.4c00015

Stacking van der Waals crystals allows for the on-demand creation of a periodic potential landscape to tailor the transport of quasiparticle excitations. We investigate the diffusion of photoexcited electron-hole pairs, or excitons, at the interface of WS2/WSe2 van der Waals heterostructure over a wide range of temperatures. We observe the appearance of distinct interlayer excitons for parallel and antiparallel stacking and track their diffusion through spatially and temporally resolved photoluminescence spectroscopy from 30 to 250 K. While the measured exciton diffusivity decreases with temperature, it surprisingly plateaus below 90 K. Our observations cannot be explained by classical models like hopping in the moire potential. A combination of ab initio theory and molecular dynamics simulations suggests that low-energy phonons arising from the mismatched lattices of moire heterostructures, also known as phasons, play a key role in describing and understanding this anomalous behavior of exciton diffusion. Our observations indicate that the moire potential landscape is dynamic down to very low temperatures and that the phason modes can enable efficient transport of energy in the form of excitons.

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