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Disorder-Induced Eigenstate Localization of Molecular Polaritons Despite Spectroscopic Strong Coupling

Year: 2026
Type: preprint
Abstract: Molecular polaritons are hybrid light--matter states whose collective character is associated with a molecular excitation extended across many molecules. However, clearly resolved polariton peaks do not by themselves establish that the corresponding eigenstates retain this molecular delocalization. Here, we use a disordered Tavis--Cummings model to distinguish spectral signatures of strong coupling from eigenstate-level molecular delocalization of electronic polaritons. Static energetic disorder can strongly reduce the molecular extent of optically visible polariton states while resolved polariton peaks persist and their apparent separation can even increase. We quantify this crossover using complementary molecular localization measures applied to individual optically visible eigenstates and the photon-weighted bright sector. Finite-size scaling shows a stable large-ensemble crossover; for Gaussian disorder, retaining approximately half of the homogeneous molecular extent requires a collective coupling roughly seven times the Gaussian disorder standard deviation $σ$, although the numerical scale depends on the disorder distribution. Including cavity and molecular linewidths through a non Hermitian Hamiltonian reveals a contrasting spectral and eigenstate response: finite linewidths reduce spectral resolvability, while cavity--molecule linewidth imbalance shifts the localization crossover to larger static disorder by suppressing the disproportionate contribution of near-resonant molecular transitions. Spectroscopic strong coupling and eigenstate-level molecular delocalization therefore characterize distinct properties and need not evolve in parallel under disorder and dissipation.
DOI: 10.48550/arxiv.2607.09559
Language: English
Open Access status: green
OpenAlex ID: W7168141945
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