Observation of a rich diversity of exciton-polaritons in Ag-CNTs bilayers*

We demonstrate strong coupling between s- and p-polarized polaritons and the S22 transition in (6,5) carbon nanotubes (CNTs) as well as p-polarized polaritons and the S11 transition, in Ag-CNT thin film bilayers. Employing angle-resolved photoreflectance in the Kretschmann-Raether (K-R) configuration, we first show strong coupling between the p-polarized surface plasmon mode and the ground state S11 exciton. We find Rabi splitting of ~100 meV which is ~8% of the S11 exciton energy (1.24 eV), approaching the ultrastrong coupling limit. By varying the thickness of the CNT layer, we are able to observe higher energy polariton modes in both polarizations that couple to the S22 transition.  

We describe the experimental apparatus, sample optimization, and prospects for pushing the coupling strength higher.  

Finally, we optimize the system for strong coupling in water and discuss progress towards controlling electrochemical redox reactions with strong coupling-modified CNT working electrodes.