  High-reflectance in many state-of-the-art optical devices is achieved with
noble metals. However, metals are limited by losses, and for certain
applications, by their high mass density. Using a combination of ab initio and
optical transfer matrix calculations, we evaluate the behavior of
graphene-based \AA-scale metamaterials and find that they could act as
nearly-perfect reflectors in the mid-long wave infrared (IR) range. The low
density of states for electron-phonon scattering and interband excitations
leads to unprecedented optical properties for graphene heterostructures,
especially alternating atomic layers of graphene and hexagonal boron nitride,
at wavelengths greater than $10~\mu$m. At these wavelengths, these materials
exhibit reflectivities exceeding 99.7% at a fraction of the weight of noble
metals, as well as plasmonic mode confinement and quality factors that are
greater by an order of magnitude compared to noble metals. These findings hold
promise for ultra-compact optical components and waveguides for mid-IR
applications. Moreover, unlike metals, the photonic properties of these
heterostructures could be actively tuned via chemical and/or electrostatic
doping, providing exciting possibilities for tunable devices.
