Spatially resolved electron tunneling spectroscopy on single crystalline Rb3C60

Fullerenes and carbon derivatives: From insulators to superconductors

“…6 to 5 . 2 meV corresponding to a reduced energy gap ratio 2¢ /kB Tc between two and four, while dI /dV follows nonetheless the BCS expression, corrected by the usual broadening with the Dynes approach [142,143]. Moreover, this latter tunnelling experiment shows that slight variations in the DOS exist even on the molecular scale [143].…”

“…More recent scanning microscopy tunnelling investigations Rb3C60 single crystals also reveal a spatial variation in the superconducting energy gap, which is attributed to a varying stoichiometry on a scale of 50 nm [143].…”

Superconductivity in fullerides

“…An early measurement of ∆ was performed using point contact tunneling in STM, giving 2∆/T c = 5.3 for Rb 3 C 60 (Zhang et al, 1991b). Later STM measurements on single crystals have given reduced gaps 2∆/T c = 5.4 (Jess et al, 1994) and 2∆/T c = 2.0 − 4.0 (Jess et al, 1996). The variations in 2∆/T c were ascribed to variations in the local stoichiometry at the tip position.…”

BCS-like Density of States in SuperconductingA3C60Surfaces

“…More surface-sensitive experimental techniques, on the other hand, like tunneling and photoelectron spectroscopy, produce results that differ considerably among each other. Tunneling spectroscopy studies [11,[16][17][18][19], for example, yield values for the reduced gap ranging from 2 to 5, probably depending on sample preparation and handling. One problem with these tunneling measurements is that none of them were carried out in ultrahigh vacuum (UHV) conditions, so that the actual state of the surface is unknown.…”