Near-field radiative heat transfer exhibits various effects, such as amplification due to the geometry of the system. In this work, we construct a periodic layered structure which consists of multiple layers of alternating materials. Radiative heat transfer (RHT) between nanoparticles placed on each side of an intermediate structure is studied. Thermal energy exchange between nanoparticles is assisted by transmitted evanescent fields, which is theoretically included in the system's Green's function. We show that the resulting heat transfer with the assistance of a multilayered structure is more than five orders of magnitude higher than that in the absence of the multilayered structure at the same interparticle distance. This increase is observed over a broad range of distances ranging from near to far field. This is due to the fact that the intermediate multilayered structure supports hyperbolic phonon polaritons, where the edge frequencies of the type-I and type-II reststrahlen bands coincide at a value that is approximately equal to the nanoparticle resonance. This allows high-k evanescent modes to resonate with the nanoparticles. The effects of the number of layers and fill factor in the multilayered structure on RHT are examined. Finally, we show that when there is a lateral distance between the two particles assisted by the interference of surface waves, RHT conductance exhibits an oscillating and nonmonotonic behavior with respect to the lateral distance between nanoparticles. These results illustrate a powerful method for regulating energy transport in particle systems and can be relevant for effective energy management at nano-micro scales.

Metasurfaces, the two-dimensional (2D) counterpart of metamaterials, have recently attracted a great deal ofattention due to their amazing properties, including negative refraction, hyperbolic dispersion, and manipulationof the evanescent spectrum. In this work, a theory model is proposed for the near field radiative heat transfer(NFRHT) between two nanoparticles in the presence of an anisotropic metasurface. Specifically, the metasurfaceis modeled as an array of graphene strips (GS), which is an ideal platform to implement any metasurfacetopology, ranging from isotropic to hyperbolic propagation. The NFRHT between two nanoparticles aresignificantly amplified when they are placed in the proximity of the GS, and regulated over several ordersof magnitude. In this configuration, the anisotropic surface plasmon polaritons (SPPs) supported by the GSare excited and provide a new channel for the near-field energy transport. The dependence of conductancebetween two nanoparticles on the orientation, the structure parameters, the chemical potential of the GS, andthe interparticle or the particle-surface distances are analyzed by clearly identifying the characteristics of theanisotropic SPPs such as dispersion relations, propagation length, and decay length. These results demonstrate apowerful method to regulate the energy transport in particle systems, and create a way to explore the anisotropicoptical properties of the metasurface based on the measured heat transfer properties.

Light-matter interactions in conventional nanophotonic structures typically lack directionality. For example, differently from microwave antenna systems, most optical emitters (e.g., excited atoms/molecules and simple nanoantennas) exhibit quasi-isotropic dipolar radiation patterns with low directivity. Furthermore, surface waves supported by conventional material substrates do not usually have a preferential direction of propagation, and their wavefront tends to spread as it propagates along the surface, unless the surface or the excitation is properly engineered and structured. In this article, we theoretically demonstrate the possibility of realizing unidirectional and diffractionless surface plasmon polariton modes on a nonreciprocal platform, namely, a gyrotropic magnetized plasma. Based on a rigorous Green’s function approach, we provide a comprehensive and systematic analysis of all the available physical mechanisms that may bestow the system with directionality, both in the sense of one-way excitation of surface waves and in the sense of directive diffractionless propagation along the surface. The considered mechanisms include (i) the effect of strong and weak forms of nonreciprocity, (ii) the elliptic-like or hyperbolic-like topology of the modal dispersion surfaces, and (iii) the source polarization state, with the associated possibility of chiral surface-wave excitation governed by angular-momentum matching. We find that three-dimensional gyrotropic plasmonic platforms support a previously unnoticed wave-propagation regime that exhibit several of these physical mechanisms simultaneously, allowing us to theoretically demonstrate unidirectional surface plasmon polariton modes that propagate as a single ultranarrow diffractionless beam. We also assess the impact of dissipation and nonlocal effects. Our theoretical findings may enable a new generation of plasmonic structures and devices with highly directional response.