Ab-initio simulation of many-body effects in high-harmonic generation in monolayer WS₂

In materials where the nonlinear susceptibility is substantial, n photons with the same frequency can be combined to generate a new photon with n times the initial frequency in a process known as harmonic generation. However, the simulation of high-order nonlinear susceptibilities as a perturbation problem can become very complex as the order increases. In recent years, time-dependent simulations have been applied to the simulation of higher order susceptibilities as a method to avoid the exponential scaling in complexity with the inclusion of many-body effects. In our work, we applied a real-time nonequilibrium Green’s function method within the adiabatic GW approximation to the study of nonlinear optical susceptibilities under a continuous wave illumination in monolayer WS₂. Our results show a good agreement with previous experimental measurements and calculations of second-order susceptibilities and higher orders can be simulated without an additional increase in computational cost.