Formation, stability, and highly nonlinear optical response of excitons to intense light fields interacting with two-dimensional materials

Excitons play a key role in the linear optical response of 2D materials. However, their significance in the highly nonlinear optical response to intense mid-infrared light has often been overlooked. Using hBN as a prototypical example, we theoretically demonstrate that excitons play a major role in this process. Specifically, we illustrate their formation and stability in intense low-frequency fields, where field strengths surpass the Coulomb field binding the electron-hole pair in the exciton. Additionally, we establish a parallelism between these results and the already-known physics of Rydberg states using an atomic model. Finally, we propose an experimental setup to test the effect of excitons in the nonlinear optical response