Phonon dispersion curves of a BC3 honeycomb epitaxial sheet.

The entire phonon-dispersion curves along the $\overline{\ensuremath{\Gamma}}\mathrm{\text{\ensuremath{-}}}\overline{\mathrm{M}}$ direction of a ${\mathrm{B}\mathrm{C}}_{3}$ honeycomb sheet have been determined both experimentally and theoretically for the first time. Most of the observed curves agreed with the theoretical ones calculated on the basis of ab initio theory. From the stretching force constants of the nearest-neighbor C-C and B-C bonds, together with that of the B-B bond, we clarified the characteristic feature of the C-C and B-C bonds. From the experimental and theoretical results, we discussed the possibility of high ${T}_{c}$.