Role of the radiation-reaction electric field in the optical response of two-dimensional crystals

A classical theory of a radiating two-dimensional crystal is proposed and an expression for the radiative-reaction electric field is derived. This field plays an essential role in connecting the microscopic electromagnetic fields acting on each dipole of the crystal to the macroscopic one, via the boundary conditions for the system. The expression of the radiative-reaction electric field coincides with the macroscopic electric field radiating from the crystal and, summed to the incident electric field, generates the total macroscopic electric field.