Proceedings of nanoGe Fall Meeting 2021 (NFM21)
DOI: https://doi.org/10.29363/nanoge.nfm.2021.170
Publication date: 23rd September 2021
Photoinduced charge transfer in van der Waals heterostructures occurs on ultrafast timescales of order 100 fs, despite the weak interlayer coupling and momentum mismatch. However, little is understood about the microscopic mechanism behind it and role of the lattice in mediating this process. Here, we use ultrafast electron diffraction to directly visualize lattice dynamics in photoexcited heterostructures of WSe2/WS2 monolayers. Following selective optical excitation of WSe2, we measure surprisingly concurrent heating of both WSe2 and WS2 layers on ~1 ps timescales, two orders of magnitude faster than would be expected from the thermal phononic coupling between the layers alone. Using first-principles density functional theory calculations, we identify a fast channel, involving an electronic state hybridized across the heterostructure, for interlayer phonon-assisted transfer of photoexcited electrons between the two layers. Our calculations demonstrate that, via this channel, phonons are emitted in both layers on femtosecond timescales, consistent with the simultaneous lattice heating observed experimentally. Taken together, our work indicates strong electron-phonon coupling via layer-hybridized electronic states – a possible novel route to control thermal transport across van der Waals heterostructures.
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