Figure 2
From: The Emergence of Dirac points in Photonic Crystals with Mirror Symmetry
Evolution of A1 and B1 subbands with variation of cylinders' relative dielectric constant.
Dirac points emerge as the photonic band gap closes upon a reduction of the dielectric constant. The relative permittivity and radii adopted are {ε = 8.8, r = 0.2a} for (a) and (b), {ε = 8, r = 0.2a} for (c) and (d), {ε = 7.2, r = 0.2a} for (e) and (f). The colored shading indicates the symmetry type of the band at the corresponding point in Brillouin zone. A and B are irreducible representation of C1h group with even and odd parity respectively. We note that the bands repel along ΓX after the A1 and B1 touch and change order when the band gap closes, but the bands along XM have an unavoidable crossing giving rise to Dirac points.
