Electron-phonon interactions in twisted bilayer graphene

Interlayer electron-electron (el-el) and electron-phonon (el-ph) interactions emerge from the coupling of atomic layers in 2D heterostructures and are essential for describing their physical properties. The additional possibility of controlling the twisting angle between layers opens new possibilities for tunable devices. Raman spectroscopy is a fundamental tool to investigate el-ph interactions and the possibility of using multiple-excitation spectroscopy allows the distinction between intralayer and interlayer el-ph interactions. We will discuss a resonance Raman study of twisted bilayer graphene (TBG) samples with different twisting angles and measured using different laser lines. Results show that the extra Raman peaks that appear in the spectra come from different physical mechanisms: the intralayer process, where the el-ph scattering occurs in a single graphene layer and the other layer only imposes a periodic potential that scatters the excited electron, and the interlayer el-ph process, where the scattering occurs between states in the Dirac cones of adjacent graphene layers.