The existence of substantial Ca 3\textit{d} derived states at \textit{E}$_{F}$ in Ca-intercalated graphite superconductor CaC$_{6}$

We have performed soft x-ray photoemission studies of Ca-intercalated graphite superconductor CaC$_{6 }(T_{c}$ = 11.2 K). The valence band spectrum shows six main structures that correspond to those of calculated DOS that predicts large Ca 3$d$ contribution at the Fermi level ($E_{F})$. The Ca 2$p$ core level spectrum has a very large asymmetric line shape, suggesting the existence of Ca 3$d$ derived conduction electrons at Ca sites. These results provide spectroscopic evidence for the existence of Ca 3$d$ electrons at $E_{F}$, which probably play a crucial role for the unusually superconductivity. The electronic structure of CaC$_{6}$ is compared with the electronic structures of other graphite intercalation compounds, providing deeper understanding of the superconductivity of CaC$_{6}$.