Probing interlayer coupling in twisted single-crystal bilayer graphene by Raman spectroscopy

Twisted bilayer graphene, in which interlayer interaction plays a critical role in this coupled system, is characterized for its angle-dependent electronic and optical properties. Here, we present a systematic Raman study of single-crystal twisted bilayer graphene grains, with the spectra of each bilayer graphene precisely correlated to its twist angle using combined transmission electron microscopic technique. Van Hove singularities develop as a result of band rehybridization at the crossing Dirac cones of the two layers, giving rise to a critical twist angle that determines the energy separation between the saddle points in the band structure and the resonance Raman spectra accordingly. The 2D mode becomes sensitive to the twist angle, showing the angle-dependent position, peak width, and intensity. Our results interpreted in the framework of angle-dependent double resonance scattering provide an important experimental perspective in understanding the coupled bilayer graphene system. Copyright (c) 2014 John Wiley & Sons, Ltd.