Ultrastrong plasmon-exciton coupling in metal nanoprisms with J-aggregates.

In this Letter, ultrastrong plasmon-exciton coupling in an Ag nanoprism-J-aggregate hybrid nanostructure is reported. A localized surface plasmon wavelength of Ag nanoprisms is tunable starting from 400 to 1100 nm. Because of the large electric field localization at the corners of the nanoprisms, the observed Rabi splitting energy is higher than the previously reported Rabi splitting energies using metal nanoparticles. A giant Rabi splitting energy of more than 400 meV corresponding to ~19% of the j-band energy has been observed, thus indicating the ultrastrong coupling regime. The hybrid nanostructure of nanoprism-J-aggregate is easy to prepare in large quantities and it can be uniformly assembled on solid substrates.