  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.
