Light–matter interactions can be strongly modified by the surrounding environment. Here, we report on the first experimental observation of molecular spontaneous emission inside a highly non-local metamaterial based on a plasmonic nanorod assembly. We show that the emission process is dominated not only by the topology of its local effective medium dispersion, but also by the non-local response of the composite, so that metamaterials with different geometric parameters but the same local effective medium properties exhibit different Purcell factors. A record-high enhancement of a decay rate is observed, in agreement with the developed quantitative description of the Purcell effect in a non-local medium. An engineered material non-locality introduces an additional degree of freedom into quantum electrodynamics, enabling new applications in quantum information processing, photochemistry, imaging and sensing with macroscopic composites.

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We present an analytical description of the nonlocal optical response of plasmonic nanowire metamaterials that enable negative refraction, subwavelength light manipulation, and emission lifetime engineering. We show that dispersion of optical waves propagating in nanowire media results from coupling of transverse and longitudinal electromagnetic modes supported by the composite and derive the nonlocal effective medium approximation for this dispersion. We derive the profiles of electric field across the unit cell, and use these expressions to solve the long-standing problem of additional boundary conditions in calculations of transmission and reflection of waves by nonlocal nanowire media. We verify our analytical results with numerical solutions of Maxwell's equations and discuss generalization of the developed formalism to other uniaxial metamaterials.Nanowire-based composites have recently attracted significant attention due to their unusual and counterintuitive optical properties that include negative refraction, subwavelength confinement of optical radiation, and modulation of photonic density of states [1][2][3]. Due to relatively low loss and ease of fabrication, nanowire composites found numerous applications in subwavelength imaging, biosensing, acousto-optics, and ultrafast alloptical processing, spanning visible to THz frequencies [4][5][6][7][8]. Wire materials are a sub-class of uniaxial metamaterials that have homogeneous internal structure along one pre-selected direction. In all, this class of composites represents a flexible platform for engineering of optical landscape from all-dielectric birefringent media, to epsilon-near-zero, to hyperbolic, and epsilon-near-infinity regimes, each of which has its own class of benefits and applications [9,10].In this work, we present an analytical technique that provides adequate description of electromagnetism in wire-based metamaterials taking into account nonlocal optical response originating from the homogenization procedure. The approach can be straightforwardly extended to describe optics of coaxial-cable-like media [11] and numerous other uniaxial composites. The developed formalism reconciles the local and nonlocal effectivemedium theories often used to describe the optics of nanowire composites in different limits [12][13][14][15]. More importantly, the formalism relates the origin of optical nonlocality to collective (averaged over many nanowires) plasmonic excitation of wire composite, and provides the recipe to implement additional boundary conditions in composite structures.We illustrate the developed technique on the example of plasmonic nanowire metamaterials, formed by an array of aligned plasmonic nanowires embedded in a dielectric host. For simplicity, we fix the frequency of electromagnetic excitations and the unit cell parameters of the system, and vary only the permittivity of the wire inclusions. (The developed formalism can be readily applied for systems where both permittivity and frequency are changed at the same time.) We assume tha...

Nanowire-based plasmonic metamaterials exhibit many intriguing properties related to the hyperbolic dispersion, negative refraction, epsilon-near-zero behavior, strong Purcell effect, and nonlinearities. We have experimentally and numerically studied the electromagnetic modes of individual nanowires (meta-atoms) forming the metamaterial. High-resolution, scattering-type near-field optical microscopy has been used to visualize the intensity and phase of the modes. Numerical and analytical modeling of the mode structure is in agreement with the experimental observations and indicates the presence of the nonlocal response associated with cylindrical surface plasmons of nanowires.