Fundamental Limits to graphene plasmonics

Polaritons are hybrid excitations of light and matter that can confine the energy of long-wavelength radiation at the nano-scale. Plasmon polaritons may enable many enigmatic quantum effects including lasing, topological protection, and dipole-forbidden absorption. A necessary condition for realizing such phenomena is a long polariton lifetime, which is notoriously difficult to meet. Plasmon polaritons in graphene provide a platform for exploring light-matter interaction at the nano-scale. However, plasmonic dissipation in graphene has remained substantial and its fundamental limits remained undetermined. Here we use nanometre-scale infrared imaging to investigate propagating plasmon polaritons in high-mobility encapsulated graphene at cryogenic temperatures. In this regime, the propagation of plasmon polaritons is primarily restricted by the dielectric losses of the encapsulated layers, with a minor contribution from electron–phonon interactions. At liquid-nitrogen temperatures, the intrinsic plasmonic propagation length can exceed 50 plasmonic wavelengths, thus setting a record for highly confined and tunable polariton modes.