Ultra-strong nonlinear optical processes and trigonal warping in MoS₂ layers

Area of Science:

• Nonlinear optics
• Materials science
• Condensed matter physics

Background:

• Nonlinear optical processes like harmonic generation are crucial for applications in microscopy, therapy, and frequency conversion.
• Higher-order harmonic generation is typically less efficient than lower-order due to weaker intrinsic material responses.

Purpose of the Study:

• To investigate and report ultra-strong optical nonlinearities in monolayer MoS2 (1L-MoS2).
• To compare the harmonic generation efficiency of 1L-MoS2 with established materials like graphene.
• To elucidate the underlying physical mechanisms responsible for the observed nonlinear optical properties.

Main Methods:

• Experimental observation of harmonic generation in 1L-MoS2.
• Theoretical calculations of nonlinear response functions using a continuum-model Hamiltonian.
• Application of quantum mechanical diagrammatic perturbation theory to analyze the nonlinear response.

Main Results:

• Monolayer MoS2 exhibits exceptionally strong optical nonlinearities.
• The third harmonic generation in 1L-MoS2 is 30 times stronger than the second harmonic.
• The fourth harmonic generation is comparable in strength to the second harmonic.
• Third harmonic generation efficiency in 1L-MoS2 is approximately three times higher than that of graphene.
• Trigonal warping is identified as a key factor contributing to the enhanced nonlinear response.

Conclusions:

• Monolayer MoS2 demonstrates superior nonlinear optical properties compared to graphene for harmonic generation.
• The findings suggest that trigonal warping in 1L-MoS2 significantly boosts nonlinear optical effects.
• Similar strong nonlinearities are anticipated in other transition-metal dichalcogenides.
• This research opens avenues for developing efficient harmonic generation devices using layered materials for advanced optical technologies.