Interband resonant high-harmonic generation by valley polarized electron\u2013hole pairs

Naotaka Yoshikawa,Shogo Sasaki,Kohei Nagai,Kento Uchida,Koichiro Tanaka,Yasumitsu Miyata,Yuhei Takaguchi

doi:10.1038/s41467-019-11697-6

Naotaka Yoshikawa, Shogo Sasaki + Show 5 more

Open Access

https://doi.org/10.1038/s41467-019-11697-6

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Abstract

High-harmonic generation in solids is a unique tool to investigate the electron dynamics in strong light fields. The systematic study in monolayer materials is required to deepen the insight into the fundamental mechanism of high-harmonic generation. Here we demonstrated nonperturbative high harmonics up to 18th order in monolayer transition metal dichalcogenides. We found the enhancement in the even-order high harmonics which is attributed to the resonance to the band nesting energy. The symmetry analysis shows that the valley polarization and anisotropic band structure lead to polarization of the high-harmonic radiation. The calculation based on the three-step model in solids revealed that the electron–hole polarization driven to the band nesting region should contribute to the high harmonic radiation, where the electrons and holes generated at neighboring lattice sites are taken into account. Our findings open the way for attosecond science with monolayer materials having widely tunable electronic structures.

Highlights

High-harmonic generation in solids is a unique tool to investigate the electron dynamics in strong light fields
Monolayer transition metal dichalcogenides (TMDs), which have a finite bandgap in contrast to graphene, have attracted much attention for their exotic properties such as enhancement of luminescence derived from their indirect-to-direct bandgap transition from bulk to monolayer form[24,25], extremely large exciton binding energy[26], and valley pseudospin physics arising from inversion symmetry breaking and a large spin-orbit interaction[27,28]
By comparing the HHG and optical absorption spectra of the monolayer TMDs, we found that HHG is enhanced when it is in resonance with the optical transition due to band nesting, indicating that the interband polarization mainly contributes to the even-order HHG

Summary

Results

0 in Fig. 3d) under excitation with a polarization along the zigzag direction (Fig. 3a) have anisotropic driving processes: those created at the K point are driven in the K – Γ – K′ direction, while those created at the K’ point are driven in the K′ – M – K direction This anisotropy in turn causes anisotropic acceleration and recombination dynamics in the K and K’ bands (0

E: Armchair e–h creation

Discussion

Methods