Quantitative measurement of viscosity in two-dimensional electron fluids.

Magnetoresistance in Corbino graphene devices enables simultaneous ohmic and viscous separation, yielding quantitative electron viscosity measurements even near the viscous–ohmic crossover.

• Why it matters: Hydrodynamic transport in two-dimensional materials is promising, but measuring the key fluid parameter—electron viscosity—quantitatively has remained difficult, especially around crossover regimes.
• What they did: The authors use Corbino-shaped monolayer and bilayer graphene to disentangle ohmic and viscous transport contributions from magnetoresistance, extracting an effective electron-electron scattering rate.
• The result: In both monolayer and bilayer graphene, the scattering rate scales linearly with temperature, deviating from the T 2 Fermi-liquid expectation and matching a tomographic fluid regime prediction for two-dimensional electron systems.

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