Abstract
Solid-state materials have recently emerged as a new stage of strong-field physics and attosecond science.
The mechanism of high-harmonic generation (HHG) from solids is being scrutinized. Here we
theoretically discuss the momentum-space pictures of HHG from graphene and crystalline dielectrics
and semiconductors. Within massless Dirac fermion and tight-binding models, we rigorously derive intraband
displacement and interband transition, which form the basis for understanding solid-state HHG.
Then based on the results of simulations that solve the time-dependent Schrödinger equation for a
one-dimensional model crystal, we introduce a simple momentum-space three-step model that incorporates
intraband displacement, interband tunneling, and recombination with a valence band hole. We also
present a time-dependent density-matrix method that simulates HHG from actual three-dimensional materials
whose results are compared with experiments to increase the understanding of measurement results.
