Signatures of Multiband Effects in High-Harmonic Generation in Monolayer MoS_{2}.

Area of Science:

• Condensed matter physics
• Ultrafast optics
• Materials science

Background:

• High-harmonic generation (HHG) in solids is a powerful technique for investigating ultrafast electron dynamics and crystal symmetries.
• Understanding HHG polarization properties is crucial for advanced applications in materials characterization.

Purpose of the Study:

• To investigate the polarization characteristics of high-order harmonics generated in monolayer molybdenum disulfide (MoS2).
• To explore the influence of crystal orientation on HHG polarization relative to the incident laser field.
• To elucidate the underlying physical mechanisms responsible for observed polarization phenomena.

Main Methods:

• Experimental measurement of high-harmonic spectra and polarization in monolayer MoS2.
• Systematic variation of crystal orientation with respect to the mid-infrared laser polarization.
• Theoretical calculations to model recombination dynamics and dipole strengths involving multiple conduction bands.

Main Results:

• Observed a prominent angular shift in parallel-polarized odd harmonics for photon energies above 3.5 eV.
• This shift was found to be material-specific to MoS2.
• Calculations attributed the shift to differences in recombination dipole strengths across multiple conduction bands.

Conclusions:

• The observed polarization shift in HHG from MoS2 is a distinct phenomenon beyond crystal symmetry effects.
• This finding provides a new pathway for probing the vectorial nature of multiband recombination dipoles.
• HHG in MoS2 offers a promising platform for exploring complex electronic interactions in 2D materials.