  In recent years the study of topological phases of matter has emerged as a
very exciting field of research, both in photonics and in electronics. However,
up to now the electronic and photonic properties have been regarded as totally
independent. Here, we establish a link between the electronic and the photonic
topological phases of the same material system and theoretically demonstrate
that they are intimately related. We propose a realization of the Haldane model
as a patterned 2D electron gas and determine its optical response using the
Kubo formula. It is shown that the electronic and photonic phase diagrams of
the patterned electron gas are strictly related. In particular, the system has
a trivial photonic topology when the inversion symmetry is the prevalent broken
symmetry, whereas it has a nontrivial photonic topology for a dominant broken
time-reversal symmetry, similar to the electronic case. To confirm these
predictions, we numerically demonstrate the emergence of topologically
protected unidirectional electromagnetic edge-states at the interface with a
trivial photonic material.
