Ab Initio Investigation of Nonlinear Mode Coupling in C₆₀

Strong light fields may be used to control molecular structure, thus providing a route to new, light-induced phases of matter. In this context, we present an ab initio molecular dynamics investigation of nonlinear mode coupling in C₆₀ and show that, under suitable conditions, resonant infrared excitation induces significant structural changes in the system. Surprisingly, exciting the highest-frequency infrared mode at field strengths employed in a recent experiment [Nature 2016, 530, 461-464], we observe no significant structural change. However, when targeting the first two infrared modes using stronger fields, all Raman modes gain energy through nonlinear coupling to the infrared modes, leading to large-amplitude vibrational excitations. We find a strong response of the H_g(5) mode, which is symmetric with respect to the equilibrium structure. For sufficiently strong field, it is of the same order as the infrared modes' excitation. This encourages further investigations into the light-induced superconducting properties of alkali-doped fullerenes.