Enhanced Near‐Field Radiative Heat Transfer between Graphene/hBN Systems

Near‐field radiative heat transfer (NFRHT) can exceed the blackbody radiation limit owing to the coupled evanescent waves, implying a significant potential for energy conversion and thermal management. Coupled surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs) with small ohmic losses enable a long propagation wavelength that is essential in NFRHT. However, so far, there still lacks knowledge about the experimental investigation of the coupling of SPPs and HPPs in terms of NFRHT. In this study, the NFRHT between graphene/hexagonal boron nitride (hBN) systems that can be readily transferred onto various substrates, with a gap space of ≈400 nm is measured. NFRHT enhancements in the order of three and six times higher than the blackbody limit for graphene/hBN heterostructures and graphene/hBN/graphene multilayers, respectively are demonstrated. In addition, the largest ever radiative heat flux using graphene/hBN/graphene multilayers under similar gap space of 400 nm is obtained. Consequently, analyzing the photon tunneling modes reveal that these phenomena are consequences of coupled SPPs of graphene and HPPs of hBN. The coupling of hyperbolic phonon polaritons (HPPs) and surface plasmon polaritons (SPPs) of graphene/hBN systems in near‐field radiative heat transfer, is experimentally examined, and achieves by far the largest heat flux for gap space of ≈400 nm. HPPs and SPPs are excited in reduced frequency bands for individual hBN and graphene, and for thinner hBN the HPPs are suppressed.