  Molecular crystals are a flexible platform to induce novel electronic phases.
Due to the weak forces between molecules, intermolecular distances can be
varied over relatively larger ranges than interatomic distances in atomic
crystals. On the other hand, the hopping terms are generally small, which
results in narrow bands, strong correlations and heavy electrons. Here, by
growing K$_x$C$_{60}$ fullerides on hexagonal layered Bi$_2$Se$_3$, we show
that upon doping the series undergoes a Mott transition from a molecular
insulator to a correlated metal, and an in-gap state evolves into highly
dispersive Dirac-like fermions at half filling, where superconductivity occurs.
This picture challenges the commonly accepted description of the low energy
quasiparticles as appearing from a gradual electron doping of the conduction
states, and suggests an intriguing parallel with the more famous family of the
cuprate superconductors. More in general, it indicates that molecular crystals
offer a viable route to engineer electron-electron interactions.

Mesoscale and Nanoscale Physics;Strongly Correlated Electrons