Raman spectra of twisted bilayer graphene close to the magic angle

In this work, we study the Raman spectra of twisted bilayer graphene samples as a function of their twist-angles (theta), ranging from 0.03 degrees to 3.40 degrees, where local theta are determined by analysis of their associated moire superlattices, as imaged by scanning microwave impedance microscopy. Three standard excitation laser lines are used (457, 532, and 633 nm wavelengths), and the main Raman active graphene bands (G and 2D) are considered. Our results reveal that electron-phonon interaction influences the G band's linewidth close to the magic angle regardless of laser excitation wavelength. Also, the 2D band lineshape in the theta < 1 degrees regime is dictated by crystal lattice and depends on both the Bernal (AB and BA) stacking bilayer graphene and strain soliton regions (SP) (Gadelha et al 2021 Nature 590 405-9). We propose a geometrical model to explain the 2D lineshape variations, and from it, we estimate the SP width when moving towards the magic angle.

Automated summary

In this study, we investigated the Raman spectra of twisted bilayer graphene samples with different twist angles. The results showed that electron-phonon interaction affects the linewidth of the G band, particularly near the magic angle. The lineshape of the 2D band is determined by the crystal lattice and strain soliton regions.