  Electron-electron interactions in graphene are sufficiently strong to induce
a correlated and momentum-conserving flow such that charge carriers behave
similarly to the Hagen-Poiseuille flow of a classical fluid. In the current
work, we investigate the electronic signatures of such a viscous charge flow in
high-mobility graphene FETs. In two complementary measurement schemes, we
monitor differential resistance of graphene for different channel widths and
for different effective electron temperatures. By combining both approaches,
the presence of viscous effects is verified in a temperature range starting
from 178 K and extending up to room temperature. Our experimental findings are
supported by finite element calculations of the graphene channel, which also
provide design guidelines for device geometries that exhibit increased viscous
effects. The presence of viscous effects near room temperature opens up avenues
for functional hydrodynamic devices such as geometric rectifiers like a Tesla
valve and charge amplifiers based on electronic Venturi effect.
