Observation of unidirectional s-p orbital topological edge states in driven photonic lattices

Abstract Time-periodic modulation of static systems is a powerful method for realizing topological insulators supporting robust unidirectional edge states. So far, such realizations have relied on interactions among s orbitals, without incorporating inter-orbital couplings. Here, we propose and experimentally demonstrate higher-orbital Floquet topological insulators by introducing periodically modulated couplings between optical s and p orbitals in a bipartite square lattice. The staggered phase of the s - p couplings generates a synthetic uniform π magnetic flux per plaquette, and periodic driving opens a topological bandgap characterized by the Floquet winding number, realizing both Chern and anomalous Floquet topological insulators. Experimentally, we image topological edge modes of s - p orbitals traveling unidirectionally around a corner. Here, the topological phases are realized by a combined effect of driving and synthetic flux. Consequently, turning off the flux makes the system trivial over a range of driving parameters. Our results open a promising pathway for exploring topological phenomena by introducing the orbital degree of freedom.