  As an analogue to electrical diode, a radiative thermal diode allows
radiation to transfer more efficiently in one direction than in the opposite
direction by operating in a contactless mode. In this study, we demonstrated
that, within the framework of three-body photon thermal tunneling, the
rectification performance of three-body radiative diode can be greatly improved
by bringing graphene into the system. The system is composed of three parallel
slabs, with the hot and cold terminals of the diode coated with graphene films,
and the intermediate body made of vanadium dioxide (VO2). The rectification
factor of the proposed radiative thermal diode reaches 300 % with a 350 nm
separation distance between the hot and cold terminals of the diode. With the
help of graphene, the rectification performance of the radiative thermal diode
can be improved by over 11 times. By analyzing the spectral heat flux and
energy transmission coefficients, it was found that the improved performance is
primarily attributed to the surface plasmon polaritons (SPPs) of graphene. They
excite the modes of insulating VO2 in the forward-biased scenario by forming
strongly coupled modes between graphene and VO2, and thus dramatically enhance
the heat flux. While, for the reverse-biased scenario, the VO2 is at its
metallic state and thus graphene SPPs cannot work by three-body photon thermal
tunneling. Furthermore, the improvement was also investigated for different
chemical potentials of graphene, and geometric parameters of the three-body
system. Our findings demonstrate the feasibility of using thermal-photon-based
logical circuits, creating radiation-based communication technology, and
implementing thermal management approaches at the nanoscale.
