Comparative High-Energy Resolution Photoemission Study of K_xC_<60> and Cs_xC_<60>

Comparative high-energy resolution (ΔE～30 meV) photoemission spectroscopy has been performed for Cs_xC_ and K_xC_ to study the difference and similarity in the electronic structure near the Fermi level (E_F) between the superconducting and the non-superconducting alkali-doped C_. It was found that Cs_xC_ (0≤x≤6) is a semiconductor or an insulator in all the composition range except for 0 appears to be metallic with a finite density of states at E_F. This shows a sharp contrast with the case of K_xC_ which exhibits a relatively large density of states at E_F in the composition range of 0<x