Ultra-strong nonlinear optical processes and trigonal warping in MoS2 layers
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CitationSäynätjoki A. Karvonen L. Rostami H. Autere A. Mehravar S. Lombardo A. Norwood RA. Hasan T. Peyghambarian N. Lipsanen H. Kieu K. Ferrari AC. Polini M. Sun Z. (2017). Ultra-strong nonlinear optical processes and trigonal warping in MoS2 layers. Nature Communications, 8, 893. 10.1038/s41467-017-00749-4.
Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e.g., microscopy, therapy, and frequency conversion. However, high-order harmonic conversion is typically much less efficient than low-order, due to the weak intrinsic response of the higher-order nonlinear processes. Here we report ultra-strong optical nonlinearities in monolayer MoS2 (1L-MoS2): the third harmonic is 30 times stronger than the second, and the fourth is comparable to the second. The third harmonic generation efficiency for 1L-MoS2 is approximately three times higher than that for graphene, which was reported to have a large χ(3). We explain this by calculating the nonlinear response functions of 1L-MoS2 with a continuum-model Hamiltonian and quantum mechanical diagrammatic perturbation theory, highlighting the role of trigonal warping. A similar effect is expected in all other transition-metal dichalcogenides. Our results pave the way for efficient harmonic generation based on layered materials for applications such as microscopy and imaging.