Moiré phonons in twisted MoSe 2 –WSe 2 heterobilayers and their correlation with interlayer excitons

• Published in: 2d materials Vol. 8; no. 3; p. 35030
• Main Authors: Parzefall, Philipp, Holler, Johannes, Scheuck, Marten, Beer, Andreas, Lin, Kai-Qiang, Peng, Bo, Monserrat, Bartomeu, Nagler, Philipp, Kempf, Michael, Korn, Tobias, Schüller, Christian
• Format: Journal Article
• Language: English
• Published: 01.07.2021
• ISSN: 2053-1583; 2053-1583
• DOI: 10.1088/2053-1583/abf98e

Abstract We report about the investigation of twisted MoSe 2 homo- and MoSe 2 –WSe 2 heterobilayers by means of low-frequency Raman spectroscopy (LFRS) and low-temperature micro photoluminescence ( µ PL). In room-temperature LFRS experiments on both, twisted MoSe 2 homobilayers and twisted MoSe 2 –WSe 2 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, MoSe 2 and WSe 2 . 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 θ  = 60 ∘ + δ ) MoSe 2 –WSe 2 heterobilayer. These investigations show that spatial regions, which can be identified to be atomically reconstructed (i.e. δ  = 0 ∘ ) by the observation of an interlayer shear mode in LFRS experiments, exhibit a strong, momentum-allowed interlayer-exciton signal in low-temperature µ 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 5 ° ≲ | δ | ≲ 6 ° , exhibit no significant interlayer-exciton signals.