  Metamaterials and metasurfaces operating in the visible and near-infrared
(NIR) offer a promising route towards next-generation photodetectors and
devices for solar energy harvesting. While numerous metamaterials and
metasurfaces using metals and semiconductors have been demonstrated,
semimetals-based metasurfaces in the vis-NIR range are notably missing. Here,
we experimentally demonstrate a broadband metasurface superabsorber based on
large area, semimetallic, van der Waals PtSe2 thin films in agreement with
electromagnetic simulations. Our results show that PtSe2 is an ultrathin and
scalable semimetal that concurrently possesses high index and high extinction
across the vis-NIR range. Consequently, the thin-film PtSe2 on a reflector
separated by a dielectric spacer can absorb > 85 % for the unpatterned case and
~97 % for the optimized 2D metasurface in the 400-900 nm range making it one of
the strongest and thinnest broadband perfect absorbers to date. Our results
present a scalable approach to photodetection and solar energy harvesting,
demonstrating the practical utility of high index, high extinction semimetals
for nanoscale optics.
