Direct Evidence for Cage Conduction Band in Superconducting Cement 12CaO•7Al2O3 by Low-Energy High-Resolution Photoemission Spectroscopy

We have performed low-energy high-resolution photoemission spectroscopy of a superconducting cement 12CaO center dot 7Al(2)O(3) (C12A7). By using the bulk-sensitive xenon-plasma light, we clearly observed a small but well-defined peak at the Fermi level (E-F). Comparison with the band calculations suggests that the observed near-E-F peak is ascribed to the conduction electrons distributed over the crystal cages responsible for the metallic nature and superconductivity of C12A7.