  We realize an unpaired Dirac cone at the center of the first Brillouin zone,
using a gyromagnetic photonic crystal with broken square sub-lattice symmetry
and broken time reversal symmetry. The behavior of the Dirac modes can be
described by a gyromagnetic effective medium model with near-zero refractive
index, and Voigt parameter near unity. When two domains are subjected to
opposite magnetic biases, there exist unidirectional edge states along the
domain wall. This establishes a link between topological edge states and the
surface waves of homogenous magneto-optical media.
