Fig. 5: Floquet TIs in the honeycomb lattice on reconfiguring the lattice geometry. | Nature Materials

Fig. 5: Floquet TIs in the honeycomb lattice on reconfiguring the lattice geometry.

From: A programmable topological photonic chip

Fig. 5

a, A reconfigured square lattice that is equivalent to the honeycomb lattice. b–d, Measured real-space distributions of light field in different modes: topological edge mode (b), bulk mode (c) and forbidden bandgap (d). e,f, Measured transmission spectrum (e) and calculated projected band (f) when the device works at θ = 0.08π. There are five bulk bands in one FSR, distinct from the three-particle model in a square lattice. The winding numbers \({{{\mathcal{W}}}}\) in all bulk bandgaps are unity, implying the existence of non-trivial boundary modes. g,h, Measured transmission spectrum (g) and calculated projected band (h) when the device works at θ = 0.24π. When decreasing the coupling strength to the critical point of θ = 0.19π, TPTs occur at the bandgap across ϵ = π/T, turning it into a trivial forbidden bandgap (\({{{\mathcal{W}}}}\) = 0), while other bandgaps remain non-trivial.

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