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

Abstract

We report an ultrahigh-resolution photoemission study of ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$ single crystals (${\mathit{T}}_{\mathit{c}}$=30.5 K) and the measurement of the superconducting energy gap. The crystals were cleaved at 13 K to expose the (111) plane. They show a sharp Fermi cutoff above ${\mathit{T}}_{\mathit{c}}$ and a superconducting gap opening below ${\mathit{T}}_{\mathit{c}}$ (2\ensuremath{\Delta}/${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$\ensuremath{\sim}4.1 at 13 K). The valence band shows a \ensuremath{\sim}0.15-eV-wide band near ${\mathit{E}}_{\mathit{F}}$ that is consistent with calculations, and a broad band at 0.15--1.3 eV, possibly contributed by the surface ${\mathrm{C}}_{60}$ layer.