Energy gap in superconducting fullerides: optical and tunneling studies

TL;DR

This study investigates the energy gap and superconducting properties of Rb3C60 fullerides using optical and tunneling methods, revealing BCS-like behavior with deviations suggesting intermediate coupling strength.

Contribution

It provides the first detailed optical and tunneling measurements of the energy gap in Rb3C60, demonstrating s-wave superconductivity beyond the weak coupling limit.

Findings

Energy gap 2 Delta=5.2 meV at low temperatures

Superconductivity exhibits BCS-like temperature dependence

Indications of intermediate coupling strength

Abstract

Tunneling and optical transmission studies have been performed on superconducting samples of Rb3C60. At temperatures much below the superconducting transition temperature Tc the energy gap is 2 Delta=5.2 +- 0.2meV, corresponding to 2 Delta/kB Tc = 4.2. The low temperature density of states, and the temperature dependence of the optical conductivity resembles the BCS behavior, although there is an enhanced ``normal state" contribution. The results indicate that this fulleride material is an s-wave superconductor, but the superconductivity cannot be described in the weak coupling limit.