Cavity-Mediated Hybridization of Bright and Dark Excitons in an Ultrastrongly Coupled Carbon Nanotube Microcavity

Semiconducting single-walled carbon nanotubes (SWCNTs) are ideal materials for studying strong light–matter coupling and related polaritonic phenomena at room temperature. SWCNTs possess strong, relatively narrow, optical absorption features arising from bright and dark exciton states, with the latter brightened by vibrational transitions in some cases. We show here that a strong light–matter interaction allows for the hybridization of the bright as well as the K-momentum dark exciton states of SWCNTs in an optical microcavity, mediated by a common cavity photon and exciton–phonon coupling. This hybridization is achieved in optically dense films of chirality-purified (6,5) SWCNTs integrated into microcavities via a lamination approach. Measured polariton dispersions are fit to a three-level Hopfield Hamiltonian model, evidencing high coupling strengths of g 1 as large as 230 meV between bright excitons and cavity photons (which would correspond to a Rabi splitting Ω1 = 2g 1 = 460 meV in the absence of the second oscillator) and g 2 as large as 100 meV for phonon-brightened K-momentum dark excitons and cavity photons. In addition, photoluminescence is observed from the lower polariton branch with a full width at half-maximum of only 30 meV.