Cooperative optical response of 2D dense lattices with strongly correlated dipoles

We study light propagation in dense low-temperature atoms on two-dimensional (2D) square and kagome lattices using a basically exact large-scale numerical computations. In the limit of weak laser intensity, shifts of the resonance line are shown in homogeneously broadened stationary samples with high atom densities, whereas the shifts are not shown in the samples with low densities. We obtain the dependence of shifts on interatomic spacing for square lattices with the various numbers of atoms, and our numerical results are in good agreement with shifts derived using a 2D isotropic infinite lattice model and experimental data for nanometric-thickness atomic ensembles in the literature.