Corner- and edge-mode enhancement of near-field radiative heat transfer

It is well established that near-field radiative heat transfer (NFRHT) can exceed Planck's blackbody limit¹ by orders of magnitude owing to the tunnelling of evanescent electromagnetic frustrated and surface modes^2-4, as has been demonstrated experimentally for NFRHT between two large parallel surfaces^5-7 and between two subwavelength membranes^8,9. However, although nanostructures can also sustain a much richer variety of localized electromagnetic modes at their corners and edges^10,11, the contributions of such additional modes to further enhancing NFRHT remain unexplored. Here we demonstrate both theoretically and experimentally a physical mechanism of NFRHT mediated by the corner and edge modes, and show that it can dominate the NFRHT in the 'dual nanoscale regime' in which both the thickness of the emitter and receiver, and their gap spacing, are much smaller than the thermal photon wavelengths. For two coplanar 20-nm-thick silicon carbide membranes separated by a 100-nm vacuum gap, the NFRHT coefficient at room temperature is both predicted and measured to be 830 W m^-2 K^-1, which is 5.5 times larger than that for two infinite silicon carbide surfaces separated by the same gap, and 1,400 times larger than the corresponding blackbody limit accounting for the geometric view factor between two coplanar membranes. This enhancement is dominated by the electromagnetic corner and edge modes, which account for 81% of the NFRHT between the silicon carbide membranes. These findings are important for future NFRHT applications in thermal management and energy conversion.