Extended Data Fig. 8: Bubble plots for the phonon dispersion of monolayer graphene. | Nature
Each vertical pair of panels is labelled at the top by the sample material and the direction: in each of these vertical pairs, the top panel exhibits the plots obtained by line shape analysis of the measured spectra, and the bottom panel presents the plots obtained by simulation (DFPT). The directions are ΓΜΓΜ (top left), ΓΚΜΚΓ (top right), Γ → the third-closest Κ (bottom left) and ΚΚ (bottom right). The plot size (cross-section) corresponds to the intensity, which has been normalized by the highest peak at each measured or calculated q. In the ΓΜΓΜ line, LO modes (170–200 meV) are visible at the second Brillouin zone along with LA modes that show up throughout. In the ΓΚΜΚΓ direction, the TO mode is additionally seen at the second Brillouin zone along the KMK line for both experiment and simulation. In the low-symmetry line (Γ → the third-closest Κ), the TA mode shows up in the latter half of the second Brillouin zone. The dispersion along the ΚΚ direction that cuts across the second Brillouin zone shows the LO mode in the first half and the TO mode in the second half in the simulation, while this asymmetric behaviour is not clearly seen in the experiment. LA and TA modes are also activated weakly at the middle of the ΚΚ line in both experiment and simulation.