Surface-plasmon-enhanced near-field radiative heat transfer between planar surfaces with a thin-film plasmonic coupler

Here, we demonstrate a substantially increased near-field radiative heat transfer between asymmetric structures (i.e., doped $\mathrm{Si}$ and ${\mathrm{Si}\mathrm{O}}_{2}$) by using a thin $\mathrm{Ti}$ film as a plasmonic coupler. The measured near-field enhancement at vacuum gap of 380 nm is found to be 3.5 times greater than that for the case without the coupler. The enhancement mechanism is thoroughly elucidated for both polarizations, and a dimensionless parameter, which can quantify the coupling strength of the surface polaritons across the vacuum interfaces, is proposed.