Photonic Chern insulators made of gyromagnetic hyperbolic metamaterials

The work addresses how to control light using artificial photonic crystals and electromagnetic metamaterials, specifically by creating photonic Chern insulators. The authors analyze and simulate gyromagnetic hyperbolic metamaterials (GHM) and argue that combining hyperbolic and gyromagnetic effects produces large topological band gaps with a gap Chern number of one. A key claimed advantage is that these Chern insulators support non-radiative chiral edge modes on their surfaces, enabling unidirectional waveguides without cladding metals that would otherwise add Ohmic loss. The edge states are reported to remain robust against disorder across a range of length scales. The study also reports that the direction of surface light flow can be flipped by reversing an applied magnetic field, and it observes negative refraction at an interface between GHMs with opposite gyromagnetic parameter signs. The authors further state that fabrication may be easier than for some other photonic topological materials.