  Coupled surface plasmon/phonon polaritons and hyperbolic modes are known to
enhance radiative transport across nanometer vacuum gaps but usually require
identical materials. It becomes crucial to achieve strong near-field energy
transfer between dissimilar materials for applications like near-field
thermophotovoltaic and thermal rectification. In this work, we theoretically
demonstrate extraordinary near-field radiative transport between a
nanostructured metamaterial emitter and a graphene-covered planar receiver.
Strong near-field coupling with two orders of magnitude enhancement in the
spectral heat flux is achieved at the gap distance of 20 nm. By carefully
selecting the graphene chemical potential and doping levels of silicon nanohole
emitter and silicon plate receiver, the total near-field radiative heat flux
can reach about 500 times higher than the far-field blackbody limit between 400
K and 300 K. The physical mechanisms are elucidated by the near-field surface
plasmon coupling with fluctuational electrodynamics and dispersion relations.
The effects of graphene chemical potential, emitter and receiver doping levels,
and vacuum gap distance on the near-field coupling and radiative transfer are
analyzed in detail.
