Graphene-enabled control of phonon polaritonic near-field radiative heat transfer in a CaCO(3) nanogap cavity.

Near-field radiative heat transfer (NFRHT) across nanometric gaps can surpass the blackbody limit by orders of magnitude evanescent waves and surface polaritons, offering exciting opportunities for ultra-compact thermal management, energy conversion and on-chip heat routing. In this work, we investigate graphene-mediated phonon polaritonic NFRHT in a CaCO nanogap cavity and clarify the underlying regulation mechanisms. Within the framework of fluctuational electrodynamics, we compute the spectral and total heat fluxes, the energy transmission coefficient, and the dispersion of the coupled modes in frequency-wavevector space. By coating graphene monolayers on the two opposing CaCO surfaces across the vacuum gap, we show that strong hybridization between graphene surface plasmon polaritons and hyperbolic phonon polaritons in CaCO markedly enhances the heat flux, yielding enhancement factors of up to 2.18 and 23.21 compared with those of bare graphene sheets and CaCO films, respectively. We demonstrate that electrostatic tuning of the graphene chemical potential enables efficient active control of the heat flux, achieving a maximum modulation ratio of about 6.85. Moreover, by introducing a relative twist angle between the optical axes of the opposing CaCO plates, we implement a twistronics-inspired strategy to tailor the dispersion and coupling strength of the hybrid modes. Jointly optimizing the twist angle and graphene electron density yields an overall modulation ratio approaching 8.04. These results provide a viable route toward compact, actively tunable thermal management devices based on graphene and anisotropic phonon-polaritonic media.