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We identify an optical excitation mechanism that can transfer a valley polarization from photo-excited electron-hole pairs to free charge carriers in twisted WSe2/MoSe2 heterobilayers. For small twist angles, the valley lifetimes of these charge carriers are surprisingly short, despite the occurrence of interlayer excitons with their presumably long recombination and polarization lifetimes. For large twist angles, we measure an increase in both the valley polarization and its respective lifetime by more than two orders of magnitude. Interestingly, in such devices we observe an interlayer transfer of valley polarization from the WSe2 layer into the MoSe2 layer. This mechanism enables the creation of a photo-induced valley polarization of free charge carriers in MoSe2, which amplitude scales with the gate-induced charge carrier density. This is in contrast to monolayer MoSe2, where such a gate-tunable valley polarization cannot be achieved. By combining time-resolved Kerr rotation, photoluminesence and angle-resolved photoemission spectroscopy measurements with first principles calcula- tions, we show that these findings can be explained by twist angle dependent interlayer scattering mechanisms involving the Q- and Γ-valleys.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Valley-polarized excitons, interlayer transfer, WSe2/MoSe2 heterobilayers

Date published: 2023-08-22

Publisher: Springer Science and Business Media LLC

Journal:

• npj 2D Materials and Applications (ISSN: 23977132) vol. 7 issue. 1 58

Funding:

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1038/s41699-023-00420-1

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Updated at: 2025-02-23 22:48:06 +0900

Published on MDR: 2025-02-23 22:48:06 +0900