Imaging viscous flow of the Dirac fluid in graphene.

The electron-hole plasma in charge-neutral graphene is predicted to realize a quantum critical system in which electrical transport features a universal hydrodynamic description, even at room temperature. This quantum critical 'Dirac fluid' is expected to have a shear viscosity close to a minimum bound, with an interparticle scattering rate saturating at the Planckian time, the shortest possible timescale for particles to relax. Although electrical transport measurements at finite carrier density are consistent with hydrodynamic electron flow in graphene, a clear demonstration of viscous flow at the charge-neutrality point remains elusive.