Enhancement of the intrinsic nonlinear response in few-atom-thick metallic films

Atomically thin films possess appealing intrinsic properties for nonlinear optics that we explore employing a rigorous quantum-mechanical description. The main optical response is driven by plasmons, the collective oscillation of conduction electrons, which are modeled through the proper consideration of the dominant features of their electronic band structure, including surface and quantum well states along with the bandgap arising for each crystallographic facet. We report a beneficial use of films decreasing in thickness down to few-atom-thick sizes, influencing both the linear and the nonlinear optical response. Such a degree of tunability makes them unique together with lower losses compared to their amorphous counterparts. These results facilitate the development of atomically-thin nonlinear nanophotonic devices based on well-defined crystalline metal films.