Metasurfaces, the two-dimensional (2D) counterpart of metamaterials, have recently attracted a great deal of attention due to their amazing properties, including negative refraction, hyperbolic dispersion, and manipulation of 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 metasurface is modeled as an array of graphene strips (GS), which is an ideal platform to implement any metasurface topology, ranging from isotropic to hyperbolic propagation. The NFRHT between two nanoparticles are significantly amplified when they are placed in the proximity of the GS, and regulated over several orders of magnitude. In this configuration, the anisotropic surface plasmon polaritons (SPPs) supported by the GS are excited and provide a new channel for the near-field energy transport. The dependence of conductance between two nanoparticles on the orientation, the structure parameters, the chemical potential of the GS, and the interparticle or the particle-surface distances are analyzed by clearly identifying the characteristics of the anisotropic SPPs such as dispersion relations, propagation length, and decay length. These results demonstrate a powerful method to regulate the energy transport in particle systems, and create a way to explore the anisotropic optical properties of the metasurface based on the measured heat transfer properties.

A thermal diode based on the asymmetric radiative heat transfer between nanoparticles assisted by nonreciprocal graphene plasmon waveguides is proposed in this work. The thermal diode system consists of two particles and a drift-biased suspended graphene sheet in close proximity of them. Nonreciprocal graphene plasmons are induced by the drift currents in the graphene sheet, and then couple to the waves emitted by the particles in near-field regime. Based on the asymmetry with respect to their propagation direction of graphene plasmons, the thermal rectification between the two particles is observed. The performance of the radiative thermal diode can be actively adjusted through tuning the chemical potential or changing the drift currents in the graphene sheet. With a large drift velocity and a small chemical potential, a perfect radiative thermal diode with a rectification coefficient extremely approaching 1 can be achieved within a wide range of interparticle distance from near to far field. The dispersion relations of the graphene plasmons are adopted to analyze the underlying physics of the rectification effect. In addition, due to the wide-band characteristic of nonreciprocal graphene plasmons, drift-biased graphene can act as a universal platform for the thermal rectification between particles. The particles with a larger particle resonance frequency are preferable to achieve a better thermal diode. This technology could find broad applications in the field of thermal management at nanoscale.

We consider the near-field radiative energy transfer between two separated parallel plates: graphene supported by a substrate and a magneto-optic medium. We first study the scenario in which the two plates have the same temperature. An electric current through the graphene gives rise to nonequilibrium fluctuations and induces energy transfer. Both the magnitude and direction of the energy flux can be controlled by the electric current and an in-plane magnetic field in the magneto-optic medium. This is due to the interplay between the nonreciprocal photon occupation number in the graphene and nonreciprocal surface modes in the magneto-optic plate. Furthermore, we report that a tunable thermoelectric current can be generated in the graphene in the presence of a temperature difference between the two plates.

The lattice Boltzmann method (LBM) is extended to solve transient radiative transfer in one-dimensional slab containing scattering media subjected to a collimated short laser irradiation. By using a fully implicit backward differencing scheme to discretize the transient term in the radiative transfer equation, a new type of lattice structure is devised. The accuracy and computational efficiency of this algorithm are examined firstly. Afterwards, effects of the medium properties such as the extinction coefficient, the scattering albedo and the anisotropy factor, and the shapes of laser pulse on time-resolved signals of transmittance and reflectance are investigated. Results of the present method are found to compare very well with the data from the literature. For an oblique incidence, the LBM results in this paper are compared with those by Monte Carlo method generated by ourselves. In addition, transient radiative transfer in a two-Layer inhomogeneous media subjected to a short square pulse irradiation is investigated. At last, the LBM is further extended to study the transient radiative transfer in homogeneous medium with a refractive index discontinuity irradiated by the short pulse laser. Several trends on the time-resolved signals different from those for refractive index of 1 (i.e. refractive-index-matched boundary) are observed and analysed.