Ultra-Broadband Super-Planckian Radiative Heat Transfer with Artificial Continuum Cavity States in Patterned Hyperbolic Metamaterial

Localized cavity resonances due to nanostructures at material surfaces can greatly enhance radiative heat transfer (RHT) between two closely placed bodies owing to stretching of cavity states in momentum space beyond light line. Based on such understanding, we numerically demonstrate the possibility of ultra-broadband super-Planckian RHT between two plates patterned with trapezoidal-shaped hyperbolic metamaterial (HMM) arrays. The phenomenon is rooted not only in HMM's high effective index for creating sub-wavelength resonators, but also its extremely anisotropic isofrequency contour. The two properties enable one to create photonic bands with a high spectral density to populate a desired thermal radiation window. At sub-micron gap sizes between such two plates, the artificial continuum states extend outside light cone, tremendously increasing overall RHT. Our study reveals that structured HMM offers unprecedented potential in achieving a controllable super-Planckian radiative heat transfer for thermal management at nanoscale.