The electronic structure of Ca-intercalated superconducting graphite CaC6

Abstract We have measured Ca-intercalated graphite superconductor CaC 6 ( T c  = 11.2 K) by soft X-ray photoemission spectroscopy in order to understand the electronic structure. For the valence band, we observed several structures that correspond to those of calculated density of states with the partial density of states of Ca 3 d at the Fermi level ( E F ). We also observed core level spectra that are a very large asymmetric Ca 2 p and asymmetric C 1 s for CaC 6 , suggesting the existence of conduction electrons derived from Ca 3 d and a charge transfer from Ca to graphene layer. These results provide spectroscopic evidence for PDOS of Ca 3 d at E F . From a comparison of electronic structure of CaC 6 and other graphite intercalation compounds (GICs), we found the difference between CaC 6 and other superconducting GICs, which provides deeper understanding of the superconductivity of CaC 6 .