Significance of the full Brillouin zone in electron-hole recollisions in solid-state high-harmonic generation

High-harmonic generation (HHG) in solids has exciting prospects for the engineeing of compact ultrafast light sources and the ultrafast probing of band structures and topology. The recollision model for HHG consisting of tunneling, propagation and recollision, has been instrumental to our understanding of HHG in the gas- and condensed-matter phases. We theoretically show that in solids, the recollision picture should be expanded to be able to describe situations of current theoretical and experimental interest. Specifically, for a bulk solid irradiated by elliptically polarized pulses and a monolayer material irradiated by linearly polarized pulses, we show that A) electron-hole pairs created away from the minimal band gap can dominate and B) the imperfect recollisions (where the electron and hole are spatially separated) can play important roles. Our methodology consists of the numerical solutions to the SBEs, an extended recollision model, and a wave-packet approach.