Abstract
We study the linear and nonlinear [second-harmonic generation (SHG)] spectra of metal monoxide (=Mg,Ca,Cd) monolayers by using a first-principles approach based on many-body theory. Our results indicate that the strongly bound excitons in with planar structure characterize the optical properties, including both linear and SHG spectra. The optical bandgap is 4.63, 3.71, and 1.27 eV, while the exciton binding energy is as large as 2.49, 2.37, and 1.13 eV, for MgO, CaO, and CdO, respectively. Moreover, the largest SHG coefficient of 586 pm/V is found in CdO monolayer with the smallest bandgap among the three materials. Most importantly, we find a linear relationship between the SHG coefficient and ( is the transferred Bader charge and is the bond length) which can be used as a descriptor to search for new two-dimensional nonlinear materials.
- Received 10 March 2021
- Revised 28 June 2021
- Accepted 8 July 2021
DOI:https://doi.org/10.1103/PhysRevMaterials.5.074005
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