The collective behaviour of particle systems that undergo frequent interparticle collisions has been studied by scientists for over 200 years under the field of hydrodynamics. A team of researchers from the University of Manchester, Lancaster University, the National Enterprise for Nanoscience (Pisa, Italy) and Istituto Italiano di Tecnologia (Genova, Italy) recently examined the behaviour and properties of graphene’s electron liquid.
Their findings demonstrated the viscous flow of electrons in graphene. This is possible as graphene hosts a unique electron system which has extremely weak electron-phonon scattering, yet electron-electron collisions are frequent enough to provide a local equilibrium above the temperature of liquid nitrogen.
As such, under certain conditions, electrons can behave as viscous liquids whilst exhibiting behaviour similar to that of classical liquids. Interestingly, the researchers found that viscous electron flow results in an anomalous voltage drop near current-injection contacts. This leads to the formation of submicrometre-sized whirlpools within the electron flow. The kinematic viscosity of the electron liquid was found to be approximately 0.1 square metres per second (i.e. 10 times higher than that of honey).