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Moiré phonons in twisted MoSe2-WSe2 heterobilayers and their correlation with interlayer excitons

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Parzefall, P 
Holler, J 
Scheuck, M 
Beer, A 
Lin, KQ 


jats:titleAbstract</jats:title> jats:pWe report about the investigation of twisted MoSejats:sub2</jats:sub> homo- and MoSejats:sub2</jats:sub>–WSejats:sub2</jats:sub> heterobilayers by means of low-frequency Raman spectroscopy (LFRS) and low-temperature micro photoluminescence (jats:italicµ</jats:italic>PL). In room-temperature LFRS experiments on both, twisted MoSejats:sub2</jats:sub> homobilayers and twisted MoSejats:sub2</jats:sub>–WSejats:sub2</jats:sub> heterobilayers, we observe moiré phonons, i.e. folded acoustic phonon modes due to the moiré superlattice. In the heterobilayers, we can identify moiré phonons of both materials, MoSejats:sub2</jats:sub> and WSejats:sub2</jats:sub>. While the twist angles for the homobilayers are relatively precisely known from the applied tear-and-stack preparation method, the twist angles of the heterobilayers have to be determined via second-harmonic-generation microscopy on monolayer regions of the samples, which has significant uncertainties. We show that by the moiré phonons of the heterobilayers, the relative twist angles can be determined on a local scale with much higher precision. We apply our technique for the investigation of a large area H-type (twist angle jats:italicθ</jats:italic> = 60jats:sup∘</jats:sup> + jats:italicδ</jats:italic>) MoSejats:sub2</jats:sub>–WSejats:sub2</jats:sub> heterobilayer. These investigations show that spatial regions, which can be identified to be atomically reconstructed (i.e. jats:italicδ</jats:italic> = 0jats:sup∘</jats:sup>) by the observation of an interlayer shear mode in LFRS experiments, exhibit a strong, momentum-allowed interlayer-exciton signal in low-temperature jats:italicµ</jats:italic>PL. On the contrary, regions, where moiré phonons are observed, i.e. which can be identified to be rigidly twisted by a misalignment angle in the range of jats:inline-formula jats:tex-math</jats:tex-math> <mml:math xmlns:mml="" overflow="scroll"> mml:mrow mml:msup mml:mn5</mml:mn> mml:mo°</mml:mo> </mml:msup> mml:mo≲</mml:mo> mml:mo|</mml:mo> mml:miδ</mml:mi> mml:mo|</mml:mo> mml:mo≲</mml:mo> mml:msup mml:mn6</mml:mn> mml:mo°</mml:mo> </mml:msup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="" xlink:href="tdmabf98eieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, exhibit no significant interlayer-exciton signals.</jats:p>



moire phonons, moire superlattice, Raman scattering, transition-metal dichalcogenides, interlayer excitons

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2D Materials

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IOP Publishing
Deutsche Forschungsgemeinschaft (KO3612-3, KO3612-4, Project ID 314695032- SFB 1277 (subproject B05), SCHU1171/10-1)