Time-dependent Hartree-Fock study of electron-hole interaction effects on high-order harmonic generation from periodic crystals

We investigate the multielectron effects on high-order harmonic generation from solid-state materials using the time-dependent Hartree-Fock theory. We find qualitative change in harmonic spectra, in particular, multiple-plateau formation at significantly lower laser intensities than within the independent-electron approximation. We reveal its origin in terms of interband polarization, i.e., electron-hole polarization, enabling interband excitation at remote crystal momenta via Coulomb potential.