Bae, SoungminMatsumoto, KanaRaebiger, HannesShudo, Ken-ichiKim, Yong-HoonHandegård, Ørjan SeleNagao, TadaakiKitajima, MasahiroSakai, YujiZhang, XiangVajtai, RobertAjayan, PulickelKono, JunichiroTakeda, JunKatayama, Ikufumi2022-08-042022-08-042022Bae, Soungmin, Matsumoto, Kana, Raebiger, Hannes, et al.. "K-point longitudinal acoustic phonons are responsible for ultrafast intervalley scattering in monolayer MoSe2." <i>Nature Communications,</i> 13, (2022) Springer Nature: https://doi.org/10.1038/s41467-022-32008-6.https://hdl.handle.net/1911/112986In transition metal dichalcogenides, valley depolarization through intervalley carrier scattering by zone-edge phonons is often unavoidable. Although valley depolarization processes related to various acoustic phonons have been suggested, their optical verification is still vague due to nearly degenerate phonon frequencies on acoustic phonon branches at zone-edge momentums. Here we report an unambiguous phonon momentum determination of the longitudinal acoustic (LA) phonons at the K point, which are responsible for the ultrafast valley depolarization in monolayer MoSe2. Using sub-10-fs-resolution pump-probe spectroscopy, we observed coherent phonons signals at both even and odd-orders of zone-edge LA mode involved in intervalley carrier scattering process. Our phonon-symmetry analysis and first-principles calculations reveal that only the LA phonon at the K point, as opposed to the M point, can produce experimental odd-order LA phonon signals from its nonlinear optical modulation. This work will provide momentum-resolved descriptions of phonon-carrier intervalley scattering processes in valleytronic materials.engThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.Journal articles41467-022-32008-6https://doi.org/10.1038/s41467-022-32008-6