  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.
