Contrasting ultrafast light-driven electron-hole interaction dynamics in monolayer MoS$_2$ and metallic NbSe$_2$

TL;DR

This study compares ultrafast electron-hole dynamics and high-harmonic generation in monolayer MoS$_2$ and NbSe$_2$, revealing material-specific differences in harmonic yield, phase, and carrier injection mechanisms.

Contribution

It introduces a multiband density matrix approach including electron-electron interactions to analyze HHG in 2D materials, highlighting distinct behaviors in semiconducting and metallic systems.

Findings

Electron-electron interactions enhance harmonic yield in MoS$_2$

Distinct optical resonances influence emission differences

Carrier injection mechanisms differ qualitatively between materials

Abstract

We study strong-field driven ultrafast dynamics and high-harmonic generation (HHG) in monolayer 2H-NbSe$_2$ and compare them with those of monolayer 2H-MoS$_2$ by solving the multiband reduced-density-matrix equations including time-dependent electron-electron interaction effects within the time-dependent Hartree + screened exchange (TD-HSEX). In MoS$_2$, these interactions strongly enhance the harmonic yield and modify the harmonic phases and angular emission patterns, wheras in NbSe$_2$ the yield enhancement is weaker but clear phase and angular changes remain. We trace these differences to the distinct optical resonances and to the different bands involved in the emission in each material. Finally, we show that carrier injection into empty bands of NbSe$_2$ differs qualitatively from interband excitation in MoS$_2$, and is well captured at a qualitative level by a Keldysh tunneling rate with a time-dependent band separation, allowing to control the timing and the region of injection of carriers to empty bands of the metal with the field parameters. Our work provides a framework to interpret ultrafast electron-hole interaction effects in experimental high harmonic generation spectra across semiconducting and metallic systems.