<p>In the far-field radiative heat transfer, only propagating waves contribute to heat transfer, and the maximum radiative heat transfer between two objects is determined by the black-body limit governed by the well-known Stefan-Boltzmann law. However, in the near-field radiative heat transfer (NFRHT), both propagating waves and evanescent waves can contribute to heat transfer. The energy carried by the evanescent waves is much larger than that by the propagating waves. As a result, the NFRHT can significantly exceed the black-body limit. The NFRHT has gained great interests due to its potential applications in thermophotovoltaics, thermal rectification, noncontact refrigeration, thermal transistors, and so on. Recent years, the studies&nbsp;of hyperbolic metamaterials show that NFRHT can be greatly enhanced&nbsp;over a broad&nbsp;frequency region via&nbsp;exciting hyperbolic phonon polaritons (HPPs).&nbsp;Besides, graphene has attracted a strong interest because it can support strongly confined surface plasmon polaritons (SPPs). The coupling between graphene plasmons and other plasmons, as well as phonon polaritons has been studied to further mediate the NFRHT. Many studies have shown that the coating of graphene can not only amplify the photon tunneling probability, but also increase the efficiency of near-field thermophotovoltaics (NFTPV). In graphene/hBN heterostructures, it has been shown&nbsp;that the total heat flux can be greatly enhanced. But it seems that in Reststrahlen bands, the coupling of the phonon polaritons in&nbsp;hBN and the surface plasmons in graphene can always suppress the photon tunneling. In this paper, we study the photon tunneling via coupling graphene plasmons with phonon polaritons in hexagonal boron nitride (hBN). We consider two cases of the optical axis of hBN along z-axis and x-axis, respectively. We investigate the NFRHT between graphene-covered bulk hBN, and compare it with that of bare bulk hBN. Our results show that in Reststrahlen bands, the coupling of graphene plasmons and phonon polaritons in hBN can either suppress or enhance the photon tunneling probability, depending on the chemical potential of graphene and frequency. This conclusion holds when the optiacal axis of hBN is either along z-axis or x-axis. The findings in this work not only deepen our understanding of coupling mechanism between graphene plasmons with phonon polaritons, but also provide a theoretical basis for controlling photon tunneling in graphene covered hyperbolic materials.</p>

Photon Tunneling via Coupling Graphene Plasmons With Phonon Polaritons of Hexagonal Boron Nitride in Reststrahlen Bands

Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2021/volume/84874

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