G band enhancement in ABt-twisted trilayer graphene

G band, originating from the in-plane vibrations of carbon atoms, is the main signature in Raman spectroscopy of graphene-based systems. It is often used to characterize the sample quality and obtain molecular vibration information. Here we investigate the Raman spectroscopy of ABt-twisted trilayer graphene (ABt-TTG) and observe two enhancement centers for the G band across samples with different twist angles. To understand the origin of these two enhancement centers, we theoretically calculate the G band intensity of ABt-TTG based on the continuum model. We find that the theoretical calculations exhibit two prominent peaks corresponding to the experimental observations after Fermi velocity corrections. We also investigated the real and imaginary parts of Raman resonances, respectively, and explained the origins of two enhancements of ABt-TTG. By using Raman spectroscopy, evolutions of band structures of ABt-TTG with respect to the twist angles can be characterized, which extends the potential applications of the Raman method in the investigation of electronic structures of graphene-based systems.