Exploring the limits of plasmons

When infrared photons are shone onto graphene, they can interact with the electrons in it to form hybrid excitations known as plasmon polaritons. Plasmons confine the energy of the micrometre-scale infrared photons to the nanoscale, and have a range of potential applications in photonic devices. However, their transport is often restricted by losses caused by placing the graphene sample between encapsulating layers. By cooling graphene in a newly designed cryogenic near-field infrared microscopy setup, Dmitri Basov and colleagues show that plasmons can propagate over 10 micometres in encapsulated graphene, placing fundamental limits on plasmon damping and electron–phonon interactions in graphene, which could have a role in other many-body phenomena such as the recently discovered unconventional superconductivity in twisted graphene bilayers.