  Superscattering, i.e., a phenomenon of the scattering cross section from a
subwavelength object exceeding the single-channel limit, has important
prospects in enhanced sensing/spectroscopy, solar cells, and biomedical
imaging. Superscattering can be typically constructed only at a single
frequency regime, and depends critically on the inescapable material losses.
Under such realistic conditions, superscattering has not been predicted nor
observed to exist simultaneously at multiple frequency regimes. Here we
introduce multifrequency superscattering in a subwavelength hyperbolic
structure, which can be made from artificial metamaterials or from
naturally-existing materials, such as hexagonal boron nitride (BN), and show
the advantage of such hyperbolic materials for reducing structural complexity.
The underlying mechanism is revealed to be the multimode resonances at multiple
frequency regimes as appear in BN due to the peculiar dispersion of
phonon-polaritons. Importantly, the multifrequency superscattering has a high
tolerance to material losses and some structural variations, bringing the
concept of multifrequency superscattering closer to useful and realistic
conditions.
