Raman Spectroscopy of Twisted Bilayer Graphene

When two periodic two-dimensional structures are superposed, any mismatch rotation angle between the layers generates a Moiré pattern superlattice, whose size depends on twisting θ. If composed by different materials, this effect is also dependent lattice parameters of each layer. superlattices commonly observed in bilayer graphene, where can be produced growing twisted graphene (TBG) samples CVD or folding monolayer back upon itself. In TBG, it was shown that coupling Dirac cones gives rise to van Hove singularities (vHs) density electronic states, energies vary with The understanding behavior electrons and their interactions phonons atomically thin heterostructures crucial for engineering novel 2D devices. Raman spectroscopy has been often used characterize heterostructures. Here, we review main important effects spectra TBG discussing firstly appearance new peaks associated wavevectors within interior Brillouin zone corresponding reciprocal unit vectors folded center reduced Zone (BZ) becoming active. Another giant enhancement G band intensity occurs only narrow range laser excitation given angle. Results show vHs states not related commensurate BZ, but mainly does necessarily have translational symmetry. Finally, there resonance mechanisms activate extra peaks: intralayer interlayer electron–phonon processes, involving same layer from layers, respectively. Both probe process kind graphene-based heterostructure, like graphene/h-BN junctions.