  The scientific community has witnessed tremendous expansion of research on
layered (i.e. two-dimensional, 2D) materials, with increasing recent focus on
applications to photonics. Layered materials are particularly exciting for
manipulating light in the confined geometry of photonic integrated circuits,
where key material properties include strong and controllable light-matter
interaction, and limited optical loss. Layered materials feature tunable
optical properties, phases that are promising for electro-optics, and a panoply
of polymorphs that suggest a rich design space for highly-nonperturbative
photonic integrated devices based on phase-change functionality. All of these
features are manifest in materials with band gap above the photonics-relevant
near-infrared (NIR) spectral band ($\sim$ 0.5 - 1 eV), meaning that they can be
harnessed in refractive (i.e. non-absorptive) applications.
