Nonlinear effects in Many-body van der Waals Interactions

Van der Waals dispersive interactions play an essential role in the stability of materials composed of layered chemically inert components. A systematic understanding of properties determining such longe ranged interactions is of great importance for heterostructures, biological or colloidal materials, as well as nanostructured devices. Many recently discovered materials, such as transition metal dichalcogenides, exhibit strong optical nonlinearity. While van der Waals interactions are studied within linear response properties, nonlinear effects are practically unexplored. In this study, we propose a generalized coupled dipole method that includes the atomic structure and the atomic linear and nonlinear polarizabilities on an equal footing. Through a modified Hamiltonian approach, the van der Waals interaction can be calculated by taking into account all many-body effects and system anisotropy. Using perturbation theory, we are able to give a qualitative comparison between factors responsible for linear and nonlinear contributions in the interaction. This investigation broadens the basic physics of dispersive interactions especially in the context of nonlinear materials.