Observation of current whirlpools in graphene at room temperature

TL;DR

This study visualizes and confirms the existence of current whirlpools in monolayer graphene at room temperature, demonstrating hydrodynamic behavior and its dependence on device size and charge neutrality.

Contribution

First direct imaging of room-temperature current vortices in graphene, validating hydrodynamic models and revealing their dependence on device parameters and charge regimes.

Findings

Current vortices are observed in graphene at room temperature.

Vortices disappear with increasing device size, confirming hydrodynamic predictions.

Vortex flow is present in both electron and hole regimes, but not near charge neutrality.

Abstract

Electron-electron interactions in high-mobility conductors can give rise to transport signatures resembling those described by classical hydrodynamics. Using a nanoscale scanning magnetometer, we imaged a distinctive hydrodynamic transport pattern - stationary current vortices - in a monolayer graphene device at room temperature. By measuring devices with increasing characteristic size, we observed the disappearance of the current vortex and thus verify a prediction of the hydrodynamic model. We further observed that vortex flow is present for both hole- and electron-dominated transport regimes, while disappearing in the ambipolar regime. We attribute this effect to a reduction of the vorticity diffusion length near charge neutrality. Our work showcases the power of local imaging techniques for unveiling exotic mesoscopic transport phenomena.