Electronic structure of superconducting KC$_8$ and non-superconducting LiC$_6$ graphite intercalation compounds: Evidence for a graphene-sheet-driven superconducting state

摘要

We have performed photoemission studies of the electronic structure inLiC$_6$ and KC$_8$, a non-superconducting and a superconducting graphiteintercalation compound, respectively. We have found that the charge transferfrom the intercalant layers to graphene layers is larger in KC$_8$ than inLiC$_6$, opposite of what might be expected from their chemical composition. Wehave also measured the strength of the electron-phonon interaction on thegraphene-derived Fermi surface to carbon derived phonons in both materials andfound that it follows a universal trend where the coupling strength andsuperconductivity monotonically increase with the filling of graphene$\pi^{\ast}$ states. This correlation suggests that both graphene-derivedelectrons and graphene-derived phonons are crucial for superconductivity ingraphite intercalation compounds.