  We investigate the electromagnetic response of staggered two-dimensional
materials of the graphene family, including silicene, germanene, and stanene,
as they are driven through various topological phase transitions using external
fields. Utilizing Kubo formalism, we compute their optical conductivity tensor
taking into account the frequency and wave vector of the electromagnetic
excitations, and study its behavior over the full electronic phase diagram of
the materials. We also consider the plasmon excitations in the graphene family
and find that nonlocality in the optical response can affect the plasmon
dispersion spectra of the various phases. The expressions for the conductivity
components are valid for the entire graphene family and can be readily used by
others.
