Theory of excitonic second-harmonic generation in monolayerMoS2

Recent experimental results have demonstrated the ability of monolayer ${\mathrm{MoS}}_{2}$ to efficiently generate second harmonic fields with susceptibilities between 0.1 and 100 nm/V. However, few theoretical calculations exist with which to interpret these findings. In particular, it is of interest to theoretically estimate the modulus of the second harmonic response since experimental reports on this differ by almost three orders of magnitude. Here, we present calculations of the second harmonic response based on a tight-binding band structure and implementation of excitons in a Bethe-Salpeter framework. We compare directly with recent experimental findings demonstrating a good agreement with the excitonic theory regarding, e.g., peak position. Furthermore, we predict an off-resonance susceptibility on the order of 0.1 nm/V, while on-resonance values rise to 4 nm/V.