Raman spectroscopy of twisted bilayer graphene

• We introduce the structural aspects of twisted-bilayer graphene.
• We discuss the production methods.
• We discuss the resonance Raman spectroscopy in this system.
• We obtain information about electron and phonon structure.

Twisted bilayer graphene (tBLG) is a two-graphene layers system with a mismatch angle θθ between the two hexagonal structures. The interference between the two rotated layers generates a superlattice with a θθ-dependent wavevector that gives rise to van Hove singularities in the electronic density of states and activates phonons in the interior of the graphene Brillouin zone. Here we review the use of Raman spectroscopy to study tBLG, exploring the θθ-dependent effects, corroborated by independent microscopy analysis. The phonon frequencies give a Raman signature of the specific tBLG, while their linewidths provide a straightforward test for tBLG structural homogeneity. Rich resonance effects, including single and multiple-resonances, intra- and inter-valley scattering events make it possible to accurately measure the energy of superlattice-induced van Hove singularities in the electronic joint density of states, as well as the phonon dispersion relation in tBLG, including the layer breathing vibrational modes.