A topological insulator (TI) features a dichotomy between insulation in the bulk and conduction along the edge. The prototypical TIs live in 2D and feature unidirectional edge waves immune to backscattering in the presence of disorders. This talk highlights the effect of inherent on-site nonlinearity on edge waves in 2D optical and mechanical TIs.
In particular, there exist topologically protected edge solitons that propagate unidirectionally immune to backscattering while maintaining their profiles due to a balance between dispersion and nonlinearity. This general principle is illustrated using two examples, the first being the photonic Floquet TI consisting of a honeycomb lattice of helical waveguides, and the second being a mechanical TI consisting of a square lattice of coupled pendulums.