Akito Masuhara

We investigate topological edge states in one-dimensional metal–dielectric photonic crystals (MDPCs) with small-molecule organic semiconductors serving as the dielectric layers. The topological states are controlled by modulating asymmetry in the metal mirror thickness, which drives a Peierls-like transition. As the Peierls bandgap closes, mid-band crystalline modes migrate toward the crystal boundaries, become edge-localized and nearly degenerate, and a new gap reopens among the remaining bulk states, as identified by quasi-normal mode analysis and calculated field profiles. The reopening is accompanied by band-edge parity inversion consistent with Zak phase predictions derived from Bloch-field symmetry and reflection-phase analysis. Experimentally measured transmission spectra track the calculated evolution of these resonant modes with mirror-thickness modulation. A computational heterostructure formed by concatenating two MDPCs with distinct Zak phases supports domain-wall resonances exclusively within the common Peierls gaps, while no states appear in the main bandgaps, consistent with surface-impedance predictions. Reflection measurements further reveal interface states at the metal/MDPC boundary, consistent with Tamm plasmon polaritons, emerging selectively within the Peierls gaps. These results provide complementary experimental and computational signatures of the underlying gap topology and establish MDPCs as a versatile and experimentally accessible platform for tunable topological photonics.

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