Evidence for local spots of viscous electron flow in graphene at moderate mobility

TL;DR

This study uses scanning probe microscopy to reveal viscous electron flow in graphene at room temperature, showing that such flow occurs even at moderate mobility levels and can be manipulated by disorder.

Contribution

It provides direct surface potential evidence of viscous electron flow in graphene at moderate mobility, expanding understanding of hydrodynamic behavior in practical devices.

Findings

Large areas near charge neutrality show opposing electric fields.

Electron-electron scattering dominates in these regions.

Ion bombardment reduces inverted fields, confirming viscous flow control.

Abstract

Dominating electron-electron scattering enables viscous electron flow exhibiting hydrodynamic current density patterns such as Poiseuille profiles or vortices. The viscous regime has recently been observed in graphene by non-local transport experiments and mapping of the Poiseuille profile. Here, we probe the current-induced surface potential maps of graphene field effect transistors with moderate mobility using scanning probe microscopy at room temperature. We discover micron-sized large areas appearing close to charge neutrality that show current induced electric fields opposing the externally applied field. By estimating the local scattering lengths from the gate dependence of local in-plane electric fields, we find that electron-electron scattering dominates in these areas as expected for viscous flow. Moreover, we suppress the inverted fields by artificially decreasing the electron-disorder scattering length via mild ion bombardment. These results imply that viscous electron flow is omnipresent in graphene devices, even at moderate mobility.