In this Letter, we have demonstrated the possibility to efficiently relay the radiative heat flux between two nanoparticles by opening a smooth channel for heat transfer. By coating the nanoparticles with a silica shell and modifying the substrate with multilayered graphene sheets, respectively, the localized phonon polaritons excited near the nanoparticles can couple with the multiple surface plasmon polaritons near the substrate to realize the heat relay at a long distance. The heat transfer can be enhanced by more than six orders of magnitude, and the relay distance can be as high as 35 times in the far-field regime. This work may provide a way to realize the energy modulation or thermal communications especially at long distances.

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.

We show that the energy-transport efficiency in a chain of two-level emitters can be drastically enhancedby the presence of a photonic topological insulator (PTI). This is obtained by exploiting the peculiarproperties of its nonreciprocal surface plasmon polariton (SPP), which is unidirectional, and immune tobackscattering, and propagates in the bulk band gap. This amplification of transport efficiency can be asmuch as 2 orders of magnitude with respect to reciprocal SPPs. Moreover, we demonstrate that despite thepresence of considerable imperfections at the interface of the PTI, the efficiency of the SPP-assisted energytransport is almost unaffected by discontinuities. We also show that the SPP properties allow energytransport over considerably much larger distances than in the reciprocal case, and we point out aparticularly simple way to tune the transport. Finally, we analyze the specific case of a two-emitter chainand unveil the origin of the efficiency amplification. The efficiency amplification and the practicaladvantages highlighted in this work might be particularly useful in the development of new devicesintended to manage energy at the atomic scale.

We show that the energy-transport efficiency in a chain of two-level emitters can be drastically enhancedby the presence of a photonic topological insulator (PTI). This is obtained by exploiting the peculiarproperties of its nonreciprocal surface plasmon polariton (SPP), which is unidirectional, and immune tobackscattering, and propagates in the bulk band gap. This amplification of transport efficiency can be asmuch as 2 orders of magnitude with respect to reciprocal SPPs. Moreover, we demonstrate that despite thepresence of considerable imperfections at the interface of the PTI, the efficiency of the SPP-assisted energytransport is almost unaffected by discontinuities. We also show that the SPP properties allow energytransport over considerably much larger distances than in the reciprocal case, and we point out aparticularly simple way to tune the transport. Finally, we analyze the specific case of a two-emitter chainand unveil the origin of the efficiency amplification. The efficiency amplification and the practicaladvantages highlighted in this work might be particularly useful in the development of new devicesintended to manage energy at the atomic scale.

Heat flux exchanged between two hot bodies at subwavelength separation distances can exceed the limitpredicted by the blackbody theory. However, this super-Planckian transfer is restricted to these separationdistances. Here we demonstrate the possible existence of a super-Planckian transfer at arbitrary large separationdistances if the interacting bodies are connected in the near field with weakly dissipating hyperbolic waveguides.This result opens the way to long-distance transport of near-field thermal energy.

We investigate the quantum optical torque on an atom interacting with an inhomogeneous electromagneticenvironment described by the most general linear constitutive relations. The atom is modeled as a two-levelsystem prepared in an arbitrary initial energy state. Using the Heisenberg equation of motion (HEM) and underthe Markov approximation, we show that the optical torque has a resonant and nonresonant part, associated,respectively, with a spontaneous-emission process and Casimir-type interactions with the quantum vacuum,which can both be written explicitly in terms of the system Green function. Our formulation is valid forany three-dimensional inhomogeneous, dissipative, dispersive, nonreciprocal, and bianisotropic structure. Weapply this general theory to a scenario in which the atom interacts with a material characterized by strongnonreciprocity and modal unidirectionality. In this case, the main decay channel of the atom energy is representedby the unidirectional surface waves launched at the nonreciprocal material-vacuum interface. To provide relevantphysical insight into the role of these unidirectional surface waves in the emergence of nontrivial optical torque,we derive closed-form expressions for the induced torque under the quasistatic approximation. Finally, weinvestigate the equilibrium states of the atom polarization, along which the atom spontaneously tends to aligndue to the action of the torque. Our theoretical predictions may be experimentally tested with cold Rydbergatoms and superconducting qubits near a nonreciprocal material. We believe that our general theory may findbroad application in the context of nanomechanical and biomechanical systems.