Journal
ACS NANO
Volume 14, Issue 1, Pages 708-714Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.9b07555
Keywords
nonlinear optics; sum frequency generation; exciton; two-dimensional semiconductors; van der Waals heterostructures; confocal microscopy; valleytronics
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Funding
- Programmable Quantum Materials, an Energy Frontier Research Center - U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) [DE-SC0019443]
- core research programs within the Materials/Chemistry and Nanoscience Focus Areas
- ASEE postdoctoral associate program at NRL
- NRC postdoctoral associate program at NRL
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We report continuous-wave second harmonic and sum frequency generation from two-dimensional transition metal dichalcogenide monolayers and their heterostructures with pump irradiances several orders of magnitude lower than those of conventional pulsed experiments. The high nonlinear efficiency originates from above-gap excitons in the band nesting regions, as revealed by wavelength-dependent second order optical susceptibilities quantified in four common monolayer transition metal dichalcogenides. Using sum frequency excitation spectroscopy and imaging, we identify and distinguish one- and two-photon resonances in both monolayers and heterobilayers. Data for heterostructures reveal responses from constituent layers accompanied by nonlinear signal correlated with interlayer transitions. We demonstrate spatial mapping of heterogeneous interlayer coupling by sum frequency and second harmonic confocal microscopy on heterobilayer MoSe2/WSe2.
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