Excitonic switching across a Z 2 topological phase transition: From Mott-Wannier to Frenkel excitons in organic materials
Résumé
Controllable topological phase transitions in low dimensional materials allows for unconventional optical selection rules and exciton series. We show that the broad mixing of single-particle contributions to the exciton states occurring across a Z2 phase transition in 1D polyacene polymers leads to an extreme tunability of optical properties, with exciton dispersions ranging from gigantic
bandwidth (≈ 1.5 eV) to practically zero. The acene length transversal to the periodic axis controls the exciton localization, allowing for a cross-over from Mott-Wannier to Frenkel-like excitons and
large changes in optical gaps, singlet-triplet splittings and the orbital structure of the real-space exciton states. Our work opens appealing perspectives for the design of novel optolectronic devices.
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