Extended Data Fig. 9: Electron-phonon coupling at the interface calculated by DFPT.

a, Phonon linewidth due to electron-phonon coupling mapped on the phonon dispersion. Compared with bulk modes, the interfacial optical modes couple strongly with electrons (note that the colour map is in log scale) because both the interfacial phonon modes and the two-dimensional electron gas are highly confined at the interface. b, Electronic band structure. Three RGB channels represent electron wavefunctions projected onto atomic orbitals in the interface region (red), in cBN (green) and in diamond (blue). Dashed horizontal line is the Fermi level, which crosses a band localized near the interface, meaning the system becomes metallic due to carriers at the interface.