Frequency shift of even-order high harmonic generation in monolayer MoS₂

Abstract

Sub-optical-cycle electron dynamics in materials driven by intense laser fields can be investigated by high harmonic generation. We observed frequency shift of high harmonic spectrum near the band gap of monolayer MoS2 experimentally. Through semi-classical quantum trajectory analysis, we demonstrated that the phase of transition dipole moment varies according to the recombination timing and momentum of tunneled electrons. It results in either blue- or red-shift of harmonic frequencies, determined by the modulated energy gap by transition dipole phases (TDPs) and Berry connections. Our finding reveals the effect of TDPs on high harmonic frequency in non-central symmetric materials.

Valley-Selective High Harmonic Generation and Polarization Induced by an Orthogonal Two-Color Laser Field

“…Specifically, the two-dimensional (2D) hexagonal crystals, such as the graphene and transition metal dichalcogenides (TMDs), have always been the quite suitable and fashionable target media for the HHG in solids because of their extraordinary transport properties. The characteristics of HHG from 2D hexagonal materials have been widely researched in both theory [26][27][28] and experiment [29][30][31][32].…”