First-principles calculation of superconductivity in hole-doped LiBC: $T_c=65\mathrm{}\mathrm{K}$

The lattice-dynamical properties of ${\mathrm{Li}}_x\mathrm{BC}$ are calculated for several values of x using density-functional perturbation theory. We find that the electron-phonon coupling parameter $\lambda$ increases monotonically with decreasing x to a maximum value of 1.4 for $x=0.125,$ owing to the increasing radius of multiply nested Fermi surface cylinders. The B-C bond-stretching phonon modes have frequencies that are 28% higher than the equivalent modes in ${\mathrm{MgB}}_2.$ This combination results in a $T_c$ of about 65 K for $x=\mathrm{0.5.}\mathrm{}$