Berlin 2024 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 88: 2D Materials and Heterostuctures: (Twisted) Bilayers (joint session HL/TT)

TT 88.6: Vortrag

Freitag, 22. März 2024, 10:45–11:00, EW 201

Confocal SHG microscopy of twisted bilayers of MoS₂ — •Nikita V. Siverin¹, Daniel J. Gillard², Dmitri R. Yakovlev¹, Alexander I. Tartakovskii², and Manfred Bayer¹ — ¹TU Dortmund, Dortmund, Germany — ²The University of Sheffield, Sheffield, UK

We investigate the crystal and exciton symmetries in twisted MoS₂ bilayer flakes using second harmonic generation (SHG). By measuring and modeling the full dependence of the SHG signal on the linear polarization angles of incident and emitted light we reveal the underlying mechanisms of SHG. Our method employs a confocal microscopy setup, allowing for spectroscopic investigations of different excitonic resonances.

Twisting layers of 2D materials is a familiar technique that produces a superlattice and gives rise to the phenomena called moiré structure inducing changes in optical properties.

We measured different regions of overlapping flakes: monolayer, twisted monolayers, bilayer and twisted bilayers. We observe strong SHG signal from monolayers and we can measure twisted angle by polarization anisotropies of the SHG signal. According to group theory, SHG is forbidden in bilayers, but we observe small signal with rotational anisotropy deviating from the one for monolayers.

Keywords: SHG; non-linear; twisted; 2D; TMDC