Enhancing superconductivity in A3 C60 fullerides

Motivated by the recent experimental report of a possible light-induced superconductivity in K3C60 at high temperature [Mitrano, Nature 530, 451 (2016)NATUAS0028-083610.1038/nature16522], we investigate theoretical mechanisms for enhanced superconductivity in A3C60 fullerenes. We find that an "interaction imbalance" corresponding to a smaller value of the Coulomb matrix element for two of the molecular orbitals in comparison to the third one, efficiently enhances superconductivity. Furthermore, we perform first-principle calculations of the changes in the electronic structure and in the screened Coulomb matrix elements of K3C60, brought in by the deformation associated with the pumped T1u intramolecular mode. We find that an interaction imbalance is indeed induced, with a favorable sign and magnitude for superconductivity enhancement. The physical mechanism responsible for this enhancement consists of a stabilization of the intramolecular states containing a singlet pair, while preserving the orbital fluctuations allowing for a coherent interorbital delocalization of the pair. Other perturbations have also been considered and found to be detrimental to superconductivity. The light-induced deformation and ensuing interaction imbalance is shown to bring superconductivity further into the strong-coupling regime.