Effect of incoherent electron-hole pairs on high harmonic generation in an atomically thin semiconductor

TL;DR

This study investigates how incoherent electron-hole pairs influence high harmonic generation in atomically thin semiconductors, revealing that photo-carriers enhance certain harmonic signals and that dephasing reduces higher order harmonics.

Contribution

The paper combines experimental observations with numerical simulations to elucidate the effects of photo-carrier doping on HHG in 2D semiconductors, highlighting the roles of intraband currents and dephasing mechanisms.

Findings

Photo-carriers enhance intraband currents below the absorption edge.

Dephasing, not phase-space filling, reduces higher order harmonics.

Simulations successfully reproduce experimental HHG responses.

Abstract

High harmonic generation (HHG) in solids reflects the underlying nonperturbative nonlinear dynamics of electrons in a strong light field and is a powerful tool for ultrafast spectroscopy of electronic structures. Photo-carrier doping allows us to understand the carrier dynamics and the correlations between the carriers in the HHG process. Here, we study the effect of incoherent electron-hole pairs on HHG in an atomically thin semiconductor. The experimentally observed response to photo-carrier doping is successfully reproduced in numerical simulations incorporating the photo-excited carrier distribution, excitonic Coulomb interaction and electron-electron scattering effects. The simulation results reveal that the presence of photo-carriers enhances the intraband current that contributes to high harmonics below the absorption edge. We also clarify that the excitation-induced dephasing process rather than the phase-space filling effect is the dominant mechanism reducing the higher order harmonics above the absorption edge. Our work provides a deeper understanding of high harmonic spectroscopy and the optimum conditions for generating extreme ultraviolet light from solids.