High-order harmonic generation in solid $\rm \bf C_{60}$

Abstract: High harmonic generation (HHG) has unleashed the power of strong laser physics in solids. Here we investigate HHG from a large system, solid C${60}$, with 240 valence electrons engaging harmonic generation at each crystal momentum, the first of this kind. We employ the density functional theory and the time-dependent Liouville equation of the density matrix to compute HHG signals. We find that under a moderately strong laser pulse, HHG signals reach 15th order, consistent with the experimental results from C${60}$ plasma. The helicity dependence in solid C${60}$ is weak, due to the high symmetry. In contrast to the general belief, HHG is unsuitable for band structure mapping in C${60}$. However, we find a window of opportunity using a long wavelength, where harmonics are generated through multiple-photon excitation. In particular, the 5th order harmonic energies closely follow the transition energy dispersion between the valence and conduction bands. This finding is expected to motivate future experimental investigations.