(196e) Radiative Thermal Transport in Tunable Graphene-Based Hyperbolic Metamaterials

Radiative heat transfer between two bodies separated by nanoscale gaps is significantly enhanced due to near-field contributions. There is growing interest in understanding this mechanism at an atomic-level for technologies such as heat-assisted magnetic recording, and emerging approaches to thermoelectrics and photocatalysis. Here, we use Boltzmann Transport Theory to study the radiative thermal transport in a graphene-Al2O3 hyperbolic metamaterial that has tunable optical and thermal properties. Our model reveals that the effective thermal conductivity increases by a factor of 2-3.5 at high temperatures due to near-field contributions. This enhancement is attributed to the existence of coupled surface modes such as plasmon and phonon polaritons, which can propagate near-field radiation over several microns. To experimentally validate these predictions, we developed a 3ω technique that differentiates the radiative and non-radiative contributions to thermal conductivity for the first time. Our work offers new insights into manipulating the spectrum and intensity of near-field thermal transport for applications such as near-field thermophotovoltaics. Hyperbolic metamaterials may offer near-field enhancement at Super-Planckian intensities between an emitter and a receiver without the practical hurdle of manufacturing nanoscale vacuum gaps.