Signatures of multi-band effects in high-harmonic generation in monolayer MoS$_2$

Abstract

High-harmonic generation (HHG) in solids has been touted as a way to probe ultrafast dynamics and crystal symmetries in condensed matter systems. Here, we investigate the polarization properties of high-order harmonics generated in monolayer MoS 2 , as a function of crystal orientation relative to the mid-infrared laser field polarization. At several different laser wavelengths we experimentally observe a prominent angular shift of the parallel-polarized odd harmonics for energies above approximately 3.5 eV, and our calculations indicate that this shift originates in subtle differences in the recombination dipole strengths involving multiple conduction bands. This observation is material specific and is in addition to the angular dependence imposed by the dynamical symmetry properties of the crystal interacting with the laser field, and may pave the way for probing the vectorial character of multi-band recombination dipoles.

Characterizing Anomalous High-Harmonic Generation in Solids

“…Figures 1(b) and 1(c) show respectively the anomalous and interband HHG spectra versus α. Our results conform with the dynamical-symmetry selection rules for HHG [32], where the D 3h spatial point group of monolayer MoS 2 together with the in-plane linearly-polarized field prohibit the emission of all perpendicular harmonics at α = n60 • and odd-order harmonics at α = 30 • + n60 • , with n an integer [25,32,61,62]. The anomalous harmonics in Fig.…”

Parametric Nonlinear Optics with Layered Materials and Related Heterostructures

“…[93][94][95] HHG was recently observed in graphene and TMDs. [87,[96][97][98][99][100][101] It was demonstrated that in 1L TMDs, even harmonics mainly arise from interband polarization and show resonant behavior close to the band nesting region (C-exciton) of the first Brillouin zone due to large joint density of states (see Figure 4a), while odd harmonics are dominated by intraband currents and thus do not experience band nesting effects and monotonically decrease with increasing harmonic order. [87] The observed enhancement of the even order harmonics was attributed to the interference between signals generated from consecutive half-cycles of the pump laser field.…”