Title: Gapless surface states originated from accidentally degenerate quadratic band touching in a three-dimensional tetragonal photonic crystal,
Abstract: 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/domain-wall
states emerge under a certain condition. We analyze their physical property in
terms of an effective hamiltonian, and a good agreement between the effective
theory and numerical calculation is obtained.