Robust one-way modes in photonic crystals without an external magnetic field

Photonic crystal (PhC) consisting of a square lattice of ferrite rods with remanence in the air is theoretically investigated. It is shown that such a PhC can possess a large band gap with a nontrivial topological property. By interfacing the PhC with different cladding materials, which have (bulk-mode) band gaps with different topological properties, different types of one-way modes that are immune to backscattering are achieved in the absence of an external magnetic field. It is numerically demonstrated that by using such one-way modes, waves can be flexibly and effectively manipulated in PhC systems without almost any power loss.