Fig. 3: Phonon dispersion and group velocity.
From: Four-dimensional vibrational spectroscopy for nanoscale mapping of phonon dispersion in BN nanotubes
a, b Phonon dispersion of the h-BN flake and the BNNT along high-symmetry lines. Extracted energies are averaged among multiple BZs and shown as black dots. Solid curves are DFPT calculation for bulk h-BN crystals. c Anisotropic phonon group velocity near Γ point. Red and blue scatters are extracted from the experimental data by fitting a quadratic function near the Γ point. Black lines are derivatives of the DFPT calculated dispersion.
