Gapless surface states originating from accidentally degenerate quadratic band touching in a three-dimensional tetragonal photonic crystal

摘要

A tetragonal photonic crystal composed of high-index pillars can exhibit a frequency-isolated accidental degeneracy at a high-symmetry point in the first Brillouin zone. A photonic band gap can be formed there by introducing a geometrical anisotropy in the pillars. In this gap, gapless surface and domain-wall states emerge under a certain condition. We analyze their physical properties in terms of an effective Hamiltonian, and a good agreement between the effective theory and numerical calculation is obtained.