Gapless Domain-Wall States Originated from Accidentally Degenerate Quadratic Band Touching in a Three-Dimensional Photonic Crystal

摘要

We theoretically investigate gapless domain-wall states in a three-dimensional tetragonal photonic crystal. We first design the photonic crystal such that its band structure has an accidentally degeneracy with a quadratic band touching among four bands at a high-symmetry point in the Brillouin zone. Then, we introduce a certain symmetry breaking so that the degeneracy is lifted. The resulting band gap is shown to have gapless domain-wall states.