The electron-phonon origin of graphene $\pi^{*}$-band kink demonstrated by isotope substitution.

The sudden change (known as kink) in the $\pi^{*}$-band dispersion near the Fermi level of Li-decorated graphene is investigated by isotope substitution. A reduced kink binding energy of 8 meV emerges from the comparison between the band structures of normal (${}^{13}C$) graphene and the heavy (${}^{13}C$) one. Such shift is in excellent agreement with the expected softening of the phonon energy distribution in the heavy graphene. This provides the experimental proof of the electron-phonon coupling being the origin of this band structure sudden change at 170 meV.