 their 
 high oscillator strength and large exciton binding energies make single - walled 
 carbon nanotubes ( swcnts ) highly promising materials for the investigation 
 of strong light  
 matter interactions in the near infrared and 
 at room temperature . to explore their full potential , 
 high - quality 
 cavities  possibly with nanoscale field localization  are 
 required . here 
 , we demonstrate the room temperature formation of plasmon  
 exciton 
 polaritons in monochiral ( 6,5 ) swcnts coupled to the subdiffraction 
 nanocavities of a plasmonic crystal created by a periodic gold nanodisk 
 array . 
 the interaction strength is easily tuned by the number of swcnts 
 that collectively couple to the plasmonic crystal . 
 angle- and polarization 
 resolved reflectivity and photoluminescence measurements combined 
 with the coupled - oscillator model confirm strong coupling ( coupling 
 strength 120 mev ) . 
 the combination of plasmon  
 exciton 
 polaritons with the exceptional charge transport properties of swcnts 
 should enable practical polariton devices at room temperature and 
 at telecommunication wavelengths . 
Supplementary Material