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Published on: November 28, 2017
Extraordinary Second Harmonic Generation in tungsten disulfide monolayers
Corey Janisch1, Yuanxi Wang2, Ding Ma3
11] Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 [2] Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802.
This study reveals exceptionally high second-order nonlinear susceptibility in monolayer tungsten disulfide (WS₂), a 2D material. This discovery opens new avenues for advanced nonlinear optics and optoelectronics.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nonlinear Optics
Background:
- Two-dimensional (2D) materials offer unique optical properties due to quantum confinement.
- Second Harmonic Generation (SHG) is a key nonlinear optical phenomenon.
- Characterizing nonlinear susceptibility in 2D materials is crucial for device applications.
Purpose of the Study:
- To investigate and quantify the second-order nonlinear susceptibility of monolayer WS₂.
- To develop a theoretical framework for modeling SHG in 2D materials.
- To explore polarized SHG as a tool for probing 2D material symmetry and orientation.
Main Methods:
- Experimental investigation of SHG in monolayer WS₂ on SiO₂/Si substrates and suspended samples.
- Development of a Green's function formalism for modeling SHG with a 2D nonlinear sheet source.
- Density Functional Theory (DFT) calculations to understand the origin of nonlinear susceptibility.
Main Results:
- Monolayer WS₂ exhibits unusually large second-order nonlinear susceptibility (d(eff) ~ 4.5 nm/V), orders of magnitude higher than conventional nonlinear crystals.
- Polarized SHG successfully probed structural symmetry and crystal orientation.
- DFT calculations indicate resonance enhancement and large joint density of states as origins for the high nonlinear susceptibility, predicting d(eff) = 0.77 nm/V.
Conclusions:
- Monolayer WS₂ possesses exceptionally high nonlinear optical properties, making it a promising material for nonlinear optics.
- The developed theoretical formalism accurately models SHG in 2D materials.
- Polarized SHG is a valuable technique for characterizing 2D materials, and WS₂'s large nonlinear susceptibility is attributed to electronic structure.
