Microscopic model of Purcell enhancement in hyperbolic metamaterials

We study theoretically the dramatic enhancement of spontaneous emission in metamaterials with the hyperbolic dispersion modeled as a cubic lattice of anisotropic resonant dipoles. We analyze the dependence of the Purcell factor on the source position in the lattice unit cell and demonstrate that the optimal emitter positions needed to achieve large Purcell factors and Lamb shifts are in the local field maxima. We show that the calculated Green function has a characteristic crosslike shape, spatially modulated due to the structural discreteness. Our basic microscopic theory provides fundamental insights into the rapidly developing field of hyperbolic metamaterials