Phase diagram of alkali-doped fullerides: A rotationally-invariant slave-boson perspective

We study the phase diagram of alkali-doped fullerides ($\rm A_3C_{60}$ with $\rm A=K, Rb, Cs$) as a function of the local Coulomb interaction $U$ and the phonon-mediated Jahn-Teller coupling $J$ for various levels of electron filling. In these materials, the Jahn-Teller coupling between electrons and the vibrational modes of the $\rm C_{60}$ molecules effectively reverses the sign of the Hund's coupling, providing a source for a local s-wave pairing mechanism. Using the rotationally-invariant slave-boson formalism we investigate the phase transitions between metallic (superconducting) states and different types of Mott insulating states at either large $U$ or large $J$, revealing a correlation-induced enhancement of superconductivity in proximity of the Mott localization mechanism.