Polarization dependence of intensities Raman peaks in twisted graphene bilayer

Abstract

The polarization dependence of the Raman 2D peak intensity and the polarization independence of the G Raman peak intensity have already been established in single-layer and AB-stacked bilayer graphene. Nevertheless, this study has not been conducted for twisted bilayers. In this study, we investigate the polarization properties of Raman peaks in three distinct twisted bilayer graphene samples, each exhibiting unique characteristics: G peak resonance, the presence of R′ peaks, and D-like peaks, respectively. Our analysis reveals anisotropic behavior in the G peak only under resonance enhancement conditions and consistent polarization-dependent behavior in the 2D peak across all twisted bilayers. Furthermore, we observe a pronounced symmetric and asymmetric polarization dependence in the intensity of R′ and D-like peaks, respectively. These observations have been attributed to the strong coupling between the two layers resulting from the resonance between the van Hove singularities, which affects the behavior of the G peak, and to a double resonance effect that enhances the coupling between the nodal structure and the electron–phonon anisotropy in the intravalley and intervalley regions for R′ and D-like peaks, respectively. These findings contribute to the advancement of our understanding of twisted bilayer systems and offer opportunities for exploring more profound studies.