Electronic contributions to the Raman spectrum of twisted bilayer graphene*

Using the continuum model, we study theoretically the purely electronic contributions to the Raman spectrum of twisted bilayer graphene (tBLG) for twist angles close to the magic angle [1]. We show that non-resonant excitations of electron-hole pairs between the first minibands above and below the neutrality point lead to a peak, the position of which is determined by the twist angle. We estimate the quantum efficiency of this Raman feature as ∼10^-13, about two orders of magnitude less than the intensity of the G peak [2]. Because of its electronic origin, the new peak provides direct information about the flatness of the first minibands in tBLG.
[1] R. Bistritzer et al., PNAS 108, 12233-12237, (2011)
[2] D. Basko, Phys. Rev. B 78, 125418 –(2008)