Organic Room-Temperature Polariton Condensate in a\nHigher-Order Topological Lattice

Organic molecule\nexciton-polaritons in photonic lattices are a\nversatile platform to emulate unconventional phases of matter at ambient\ntemperatures, including protected interface modes in topological insulators.\nHere, we investigate bosonic condensation in the most prototypical\nhigher-order topological lattice: a 2D-version of the Su–Schrieffer–Heeger\nmodel. Under strong optical pumping, we observe bosonic condensation\ninto both 0D and 1D topologically protected modes. The resulting 1D\nmacroscopic quantum state reaches a coherent spatial extent of 10\nμm, as evidenced by interferometric measurements of first order\ncoherence. We account for the spatial mode patterns resulting from\nfluorescent protein-filled, structured microcavities by tight-binding\ncalculations and theoretically characterize the topological invariants\nof the lattice. Our findings pave the way toward organic on-chip polaritonics\nusing higher-order topology as a tool for the generation of robustly\nconfined polaritonic lasing states.