High-energy resolution photoemission study of Cs_xC₆₀. Comparative study with K_xC₆₀

Comparative high-energy resolution (ΔE ∼ 30 meV) photoemission spectroscopy has been performed for Cs_xC₆₀ and K_xC₆₀ 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 C₆₀. It was found that Cs_xC₆₀ (0≤x≤6) is a semiconductor or an insulator in the whole composition range except for 0<x≤1 where the Cs doped C₆₀ appears to be metallic with a finite density of states at E_F. This shows a sharp contrast with the case of K_xC₆₀ which exhibits a relatively large density of states at E_F in the composition of 0<x<4 with the largest intensity around x = 3.