Attractive interaction and superconductivity forK3C60

The ${\mathrm{K}}^{+}$-ion optic phonons couple strongly to carriers on ${\mathrm{C}}_{60}$ molecules and can lead to an effective attraction at low energies. The fcc lattice is a frustrated lattice for a charge-density-wave state, opening the door to superconductivity. The competition between these instabilities is shown explicitly within mean-field theory.