Quantitative measurement of viscosity in two-dimensional electron fluids

TL;DR

This paper introduces a method using magnetoresistance in graphene devices to quantitatively measure electron viscosity, revealing a linear temperature dependence of electron-electron scattering rates, supporting a novel tomographic flow regime.

Contribution

It provides a new experimental approach to measure electron viscosity in 2D materials and uncovers unexpected linear temperature scaling of scattering rates.

Findings

Magnetoresistance in graphene can disentangle Ohmic and viscous transport.

Electron-electron scattering rate scales linearly with temperature.

Supports the existence of a tomographic flow regime in 2D electron fluids.

Abstract

Electron hydrodynamics is an emerging framework that describes dynamics of interacting electron systems as conventional fluids. While evidence for hydrodynamic-like transport is reported in a variety of two-dimensional materials, precise quantitative measurement of the core parameter, electron viscosity, remains challenging. In this work, we demonstrate that magnetoresistance in Corbino-shaped graphene devices offers a simultaneous Ohmmeter/viscosometer, allowing us to disentangle the individual Ohmic and viscous contributions to the transport response, even in the mixed flow regime. Most surprising, we find that in both monolayer and bilayer graphene, the effective electron-electron scattering rate scales linearly with temperature, at odds with the expected $T$-squared dependence expected from conventional Fermi liquid theory, but consistent with a recently identified tomographic flow regime, which was theoretically conjectured to be generic for two-dimensional charged fluids.