Fig. 5.

(Left) Robustness against four types of impurities: (A) uniaxial dielectric impurity (${\epsilon }_{zz}=4$), (B) Tellegen impurity (${\xi }_{zz}={\zeta }_{zz}=1$), (C) chiral impurity (${\xi }_{zz}=-{\zeta }_{zz}=i$), and (D) chiral impurity with $T_p$ invariance (${\xi }_{xy}=-{\xi }_{yx}={\zeta }_{xy}=-{\zeta }_{yx}=0.3i$; other parameters are the same as superlattice) remaining invariant under $T_p$ operation. LCP point excitation source (green stars) is at a frequency of 0.6($2\pi c/a$). A cylindrical impurity with radius $r=0.11a$ is placed near the boundary. (Right) The corresponding projected bandstructures. Colorbar represents the field strength.