Merohedral disorder and impurity impacts on superconductivity of fullerenes

TL;DR

This study uses scanning tunneling microscopy to explore how merohedral disorder and impurities affect the exotic s-wave superconductivity in Rb3C60 fullerenes, revealing robustness and impurity-induced states.

Contribution

It demonstrates the resilience of s-wave superconductivity in fullerenes against disorder and impurities, and uncovers impurity-induced Yu-Shiba-Rusinov states at the atomic scale.

Findings

Superconductivity in Rb3C60 is robust against merohedral disorder and non-magnetic impurities.

Magnetic Fe adatoms induce Yu-Shiba-Rusinov states with energy and spatial variations.

High-temperature superconductivity likely driven by local electron pairing involving multiorbital correlations and phonons.

Abstract

Local quasiparticle states around impurities provide essential insight into the mechanism of unconventional superconductivity, especially when the candidate materials are proximate to an antiferromagnetic Mott-insulating phase. While such states have been reported in atom-based cuprates and iron-based compounds, they are unexplored in organic superconductors which feature tunable molecular orientation. Here we employ scanning tunneling microscopy and spectroscopy to reveal multiple forms of robustness of an exotic $s$-wave superconductivity in epitaxial Rb$_3$C$_{60}$ films against merohedral disorder, non-magnetic single impurities and step edges at the atomic scale. Also observed have been Yu-Shiba-Rusinov (YSR) states induced by deliberately incurred Fe adatoms that act as magnetic scatters. The bound states display abrupt spatial decay and vary in energy with the Fe adatom registry. Our results and the universal optimal superconductivity at half-filling point towards local electron pairing in which the multiorbital electronic correlations and intramolecular phonons together drive the high-temperature superconductivity of doped fullerenes.