Berry-Pancharatnam 1956 phase concept: photonic-band Berry curvature integrates over BZ to give Chern number; gauge invariant + topologically robust; foundation of all photonic topological invariants.
Berry-Pancharatnam 1956 phase concept: photonic-band Berry curvature integrates over BZ to give Chern number; gauge invariant + topologically robust; foundation of all photonic topological invariants.