Electronic structure and superconducting energy gap in Rb3C60 single crystals studied by photoemission spectroscopy

We report an ultrahigh-resolution photoemission study of Rb3C60 single crystals (Tc=30.5 K) and the measurement of the superconducting energy gap. The crystals were cleaved at 13 K to expose the (111) plane. They show a sharp Fermi cutoff above Tc and a superconducting gap opening below Tc (2Δ/kBTc∼4.1 at 13 K). The valence band shows a ∼0.15-eV-wide band near EF that is consistent with calculations, and a broad band at 0.15-1.3 eV, possibly contributed by the surface C60 layer.