Fig. 1

Raman results of TBG in the visible range. a, b Raman spectra in two samples of TBG with θ = 6 and 13° recorded with the 2.18 and 2.41 eV laser lines, respectively. The vertical scale, I_TBG/I_SLG, corresponds to the ratio of the peak intensities of the Raman spectra in TBG and single-layer graphene (SLG). The peak around 1620 cm⁻¹ in a is called L_a, since it comes from the LO phonon branch and is activated by the intralayer electron–phonon scattering process, whereas the peak at 1480 cm⁻¹ in b is called T_e since it comes from the TO phonon branch and is activated by the interlayer process. c, d Excitation Raman maps of the samples with θ = 6 and 13° recorded with several laser lines with photon energies in the visible range (1.9–2.7 eV). e Raman excitation profile (REP) of the G band (black squares) and the L_a peak (blue circles) of the sample with low twisting angle (θ = 6°). f REP of the G band (black squares) and of the T_e peak (green circles) of the sample with intermediate twisting angle (θ = 13°). The T_e peak intensity was multiplied by ≈ 100 times for comparison with the G-band REP and in both e, f, the error bars represent the standard deviation