Evolution of Second Harmonic Generation of WXO (X = S, Se, Te) under Strain for Real-Time Strain Detectors: A First-Principles Investigation

Two-dimensional nonlinear crystals have brought new opportunities for the miniaturization and multifunctionality of integrated optoelectronic devices. Here, we systematically study the atom and electron structure, dielectric properties, and second harmonic generation (SHG) of Janus materials WXO (X = S, Se, Te). Based on the analysis of the physical origin of a large second-order nonlinear coefficient, we further investigate the dependence of the SHG pattern intensity and rotational symmetry for Janus WTeO on stress-strain. Under biaxial strain, the second-order nonlinear coefficients show blue and red shifts by the compression and tensile strain, respectively. Meanwhile the parallel SHG intensity significantly reduces by 2 orders of magnitude. Moreover, together with the change in the nonlinear intensity, the SHG pattern clearly evolves from a labyrinth-like shape to a bubble-like shape. These results reveal the SHG evolution under stress conditions and provide a theoretical basis for the design of real-time strain sensors based on Janus WTeO.