Figure 1

(a) Raman spectra of ten TBG samples with different angles between 4.3\(^\circ\) and 10.2\(^\circ\). The spectra were acquired using four different laser lines, represented by different colours in the figure, but only those presenting the strongest resonance effect are displayed in the figure. The spectra is shown in three regions: (i) the acoustic modes (ZA, TA and LA), (ii) the out-of-plane TO phonon (oTO) and (iii) the optical modes close to the G band (iTO and LO). All spectra with \(\theta \ge 7.4^{\circ }\) were multiplied by \(10\,\times\) in the acoustic and the oTO regions for a better visualisation. (b) Positions of all peaks extracted from all Raman spectra plotted as a function of \(\theta\). The twisting angles were determined by the LA and TA phonon branches according to dispersion curves (full black lines) obtained by Cong et al.²⁹ (see text). The dashed black lines are theoretical curves of the TBG phonon frequencies²⁷ as a function of the twisting angle²⁸. The blue (green) stripe highlights the range of angles of the TBGs investigated in this work that are activated by the intralayer (interlayer) el–ph process.