Exciton-driven giant non-linear overtone signals from buckled hexagonal monolayer GaAs

Abstract

We report here a giant $\left|{\chi }_{baa}^2\right|=$780 pm/V second harmonic and $\left|{\chi }_{aaaa}^3\right|=$1.4$\times$10${}^{-17}$ m${}^2$/V${}^2$ third harmonic signal from single atomic sheet of buckled hexagonal GaAs. We demonstrate this through the solution of an ab-initio real-time Bethe-Salpeter equation by including the electron-hole screened-exchange self-energy. The coupling between time-dependent external electric field and correlated electrons is treated within the modern theory of polarization. The result of our calculation envisage monolayer GaAs to be a prominent member in the material library of non-linear signal generations.