Negative local resistance caused by viscous electron backflow in graphene

TL;DR

This paper provides experimental evidence that electrons in graphene behave as a viscous fluid, forming whirlpools and causing negative voltage drops, which advances understanding of electron hydrodynamics in two-dimensional materials.

Contribution

It demonstrates viscous electron flow in graphene with direct evidence of whirlpools and negative voltage drops, highlighting the fluid-like behavior of electrons in this material.

Findings

Negative voltage drop near current contacts in graphene

Observation of submicrometer whirlpools in electron flow

Electron viscosity in graphene estimated at ~0.1 m$^2$/s

Abstract

Graphene hosts a unique electron system in which electron-phonon scattering is extremely weak but electron-electron collisions are sufficiently frequent to provide local equilibrium above liquid nitrogen temperature. Under these conditions, electrons can behave as a viscous liquid and exhibit hydrodynamic phenomena similar to classical liquids. Here we report strong evidence for this transport regime. We find that doped graphene exhibits an anomalous (negative) voltage drop near current injection contacts, which is attributed to the formation of submicrometer-size whirlpools in the electron flow. The viscosity of graphene's electron liquid is found to be ~0.1 m$^2$ /s, an order of magnitude larger than that of honey, in agreement with many-body theory. Our work shows a possibility to study electron hydrodynamics using high quality graphene.