Artificial polariton bandgaps at infrared frequencies are investigated by exploiting the strong coupling of electromagnetic waves with induced electric dipoles in two-dimensional (2D) indium tin oxide nanorod arrays (ITO-NRAs). The electric dipoles originate from the collective oscillations of free electrons within the individual ITO nanorods undergoing plasmonic resonance. Controlling the near-field interactions among the neighboring electric dipoles allows for manipulation of the collective polariton modes that are manifested as a polariton bandgap. A theoretical model is developed to understand the coupled phenomena underlying the unique characteristics of plasmon–polariton bandgaps. With high-degree geometric control of the ITO-NRAs, it is experimentally demonstrated that reducing the spacing between ITO nanorods in a square array strengthens the near-field interactions and thus results in a redshift as well as broadening of the polariton bandgap. Furthermore, arranging ITO-NRAs in a rectangular lattice breaks the symmetry with respect to the principle axis, which leads to a splitting of the collective polariton modes owing to the competition between the quasi-longitudinally and quasi-transversely coupled plasmon–polariton modes. The work highlights the use of a classical dipole coupling method for scaling polariton bandgaps to the infrared in artificial plasmonic lattices, thereby offering a new design dimension for infrared sensing, absorbers, and optical communications.
- electric dipole coupling
- indium tin oxide nanorod arrays
- plasmon–polariton bandgaps
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics