Strongly coupled surface plasmon-exciton excitations in small-diameter carbon nanotubes

We study theoretically the interactions of excitonic states with surface electromagnetic modes of a single-walled carbon nanotube. We show that these interactions result in the exciton-plasmon coupling that is significant in its strength due to the presence of weakly-dispersive low-energy (~0.5-2 eV) interband surface plasmon modes and large exciton excitation energies ~1 eV in small-diameter nanotubes. We estimate the exciton-plasmon Rabi splitting to be ~0.1 eV which is close to that in organic semiconductors and much larger than that in hybrid semiconductor-metal nanoparticle molecules. We calculate the exciton absorption lineshape and show the line splitting effect as the exciton is tuned to the nearest interband surface plasmon resonance of the nanotube.