Figure 3
(a) Theoretical total Raman intensity for TBGs with the same angles of the experimental samples, between 4.3\(^\circ\) and 10.2\(^\circ\). All spectra were calculated using the double-resonant Raman model described in the text, which includes interlayer and intralayer el–ph processes, for the excitation energy of 1.50 eV. The intensities in the acoustic region (\(\omega <700\) \({\hbox {cm}}^{-1}\)), which shows the peaks associated to TA and LA modes, were enhanced by a factor of 100 for a better comparison with the optical region (\(\omega >1400\) \({\hbox {cm}}^{-1}\)), that shows the iTO and LO peaks. The grey strip between 1570 \({\hbox {cm}}^{-1}\) and 1600 \({\hbox {cm}}^{-1}\) denotes the region of the G band, which is a first-order process not included in the calculations. (b) Theoretical Raman spectra of TBG structures for \(\theta = 8.5^\circ\) and 4.5\(^\circ\) showing separately the intralayer (blue curves) and interlayer (green curves) processes, for the excitation energy of 1.50 eV, compared with experimental measurements (red curves). In this case, the acoustic region was magnified by a factor of 50 compared to the optical one and all the theoretical frequencies shown in the figures were shifted by \(\pm 20\) \({\hbox {cm}}^{-1}\), in the optical and the acoustic region, respectively.
